Wednesday, September 18, 2013

Propeller Static & Dynamic Thrust Calculation - Part 1 of 2

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Propeller Static & Dynamic Thrust Calculation

By: Gabriel Staples
Written: 16 July 2013
Last Updated: 13 April 2014
--made a minor correction to an example, & added a plot
--added many more statistical details in order to better explain the accuracy of the equation.
--added Simplified form of eqn. too. - 15 Oct. 2013
--added links to Part 2 of this article - 13 Apr. 2014

Other Articles:

Propeller Thrust Equation, & Downloadable Excel Spreadsheet Thrust Calculator:


Figure 1: a preview of what is to come - Static Thrust (left) & Dynamic Thrust (right).

I have been interested in propellers for a very long time.  I've also been interested in how they produce thrust, and how forward velocity affects that thrust.  Therefore, I've done a lot of thinking about it, and put a lot of time into understanding them better.  Here is an equation that I came up with to quantify the thrust produced by propellers.  I wanted it to be a simple approximation, with a minimal number of inputs.  Therefore, it uses only the propeller's pitch and diameter (from the numbers on the front of the prop), and the RPMs at which the prop is spinning (this can be measured from a basic optical tachometer such as the one shown in the picture to the left).  That's it!

Here is the equation.  

The expanded form is shown to help you see where some of the numbers come from.  The simplified form is shown to help you put the equation into a calculator or Excel spreadsheet easier.

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Blog Name Changed

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18 Sept. 2013

My blog name has now changed from "Getting Started in Electric Radio Controlled Aircraft," to " -- Knowledge, Tips & Tricks for RC."  However, all website links and addresses are unchanged.


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Monday, July 15, 2013

The "Staples Stingray" Glider Sneak Peak!

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-Bungee-launched, Free Flight....and flights up to 250 ft. altitude and 1/5 of a mile far!

...Pictures, Videos, and more...

This is a sneak peak at my $5 "Staples Stingray" free-flight, bungee-launched glider I have very recently finished designing, modifying, and testing!  The design is a modified version of the FliteTest Nutball RC airplane, which is a modified version of the original Nutball by GoldGuy.

By Gabriel Staples
Written: 15 July 2013
Updated: 19 July 2013 (added more videos)

(for links to more videos, go to the bottom of the post) 

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I have been spending quite some time now (about 3 months), figuring out how to build a SIMPLE, INEXPENSIVE free-flight glider for the Boy Scout troop I work with, and this is what I came up with!  I really think this plane does the trick, and it's tons of fun to launch, fly, and even chase and try to catch!

Here's a description of it that I wrote in my "Getting into Scratch Building...." article above.  Click the link at the top of this post to read that article as well:

"I have even prototyped and tested, for my local Boy Scout troop working on the Aviation merit badge, a $5 free-flight glider based on the NutBall, which is capable of being bungee-launched (via a home-made $25~$35 launcher) to altitudes up to 250 feet, and flying several hundred yards distance in a single flight!  My wife named it the Stingray (see photo of a stingray below), since the glider resembles a stingray flying backwards.  I would like to post the plans and video of the Stingray glider and bungee launcher when I get the chance, so other Boy Scout troops and do-it-yourselfers can make one too....

 I have also designed and tested what I call a "training fin" for the NutBall, which can easily be velcroed onto the top of the plane in order to make it self-right (roll level automatically) whenever it is banked.  This is really useful for a beginner as well.  (More to come on this; I need to write a post on it still too)."
Here are some sneak-peak photos of my new Stingray Free-flight glider below.

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Hat Cam

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Written: 15 July 2013

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Here are some pictures of my hat-camera.  No, this is not my original idea.  I got it from other people online, and simply picked up some hardware from Home Depot that I thought would work best.  Here are some photos of what I put together.  I've been using the hat cam now for a couple years and it works great!  It doesn't aim perfectly (it usually aims just a little too high when I am really close to something, and just a little too low when I am very far away), but it works well enough most of the time.  The hat was free basically, since I had plenty of them lying around, and the hardware costed something like $3 maybe.  Certainly a wise investment I'd say.

Additional pictures can be seen below:

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Wednesday, June 5, 2013

It's Not About the Nail

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Written: 6 June 2013

Actual RC-Related Articles:

A Brief Interjection:

So, I am married.  If you are too, or if you talk to any females regularly, you'll know as I know, that this concept is really hard to get (and I'm still trying to learn it :))......that is........IT'S NOT ABOUT THE NAIL!

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Monday, May 27, 2013

A Few Tips & Tricks: Arduinos, PCB Tricopter Frames, Home-made Acid Etchant for Copper

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By: Gabriel Staples
Written: 28 May 2013
Updated: 30 Oct. 2013
-added link to LadyAda's Arduino Uno FAQ
-added link to Arduino Nano V3.0 on Ebay

Other Articles You May Be Interested in Reading:

So, this month I've been dabbling into a few new RC airplane areas that I have previously not looked into.  You may wonder how these topics in the title relate to RC airplanes?  Well, for me, everything does :), so let's briefly discuss:

Arduino & Microcontrollers:

What is Arduino?  Well, Arduino is a small interface board which connects to your computer via a USB cable, and consists of an Atmel microcontroller chip, or "brain," which can do a variety of functions and processing, as well as circuitry to enable you to connect to it via a USB cable, in addition to a voltage regulator and input and output ports.  Basically, it is a development or experiment board which allows you to plug in sensors and circuitry and do anything you can imaging via your own personal ingenuity and programming skills---yet it is inexpensive and simple enough that anyone can get started.  It is especially designed for the non-programmer.  Here is Arduino's description of themselves.  A few things that make Arduino unique are its price, ease of use and programming, and the fact that it is open-source.  Open-source means that its parts, pieces, construction, and coding are all available to the public, and that its software is FREE.  This is the counterpart to "proprietary," which means that something is owned by a company and its internal workings are generally guarded and kept secret in order to prevent others from duplicating it.

You might not know it, but the microcontroller, or MCU, which is the heart of the Arduino, is a very common-place item in today's electronics.  Modern RC radio transmitters use them, for example, as well as ESCs (Electronic Speed Controllers) and "smart" battery chargers such as the Thunder AC680.
 Many UAVs (Unmanned Aerial Vehicles) use microcontroller-based autopilots!  Now, with Arduino,

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Tuesday, April 30, 2013

Beginner RC Helicopter & Quadrocopter

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By Gabriel Staples
Written: 13 Jan 2013
Last updated: 3 Dec 2016
Update History (newest on top):
-3 Dec. 2016, updated dead link to micro heli (now linked to "v911" search results on eBay), and updated links to some other small parts too
-6 Oct. 2013, added links to micro quadrocopters

Related Articles:
For those of you who have tried a 3-Channel micro helicopter or two (ex: virtually any helicopter that you might see at a mall), you are probably ready to try something a little bit better.  Well, don't go out quite yet and spend hundreds on a 6-Channel fully acrobatic collective pitch heli.  Rather, get a nice single-rotor 4-Channel beginner micro heli that can take some abuse while still teaching you more skills.  Once you master a micro 4-Channel heli, then take the step up to a several hundred dollar 6-Channel helicopter, and start flying slowly and carefully as it will be much more difficult still than the 4-channel heli.

So, which one to buy?  Well, I have the HobbyKing FP100 ($29 + shipping) (also see the "v911" eBay links below) (shown to the right), and I love it! It flies very well, gives you those extra skills you need while providing more challenge and capability, and yet is still so light that it is durable and can take quite a few crashes without breaking.  And if you break it? --you can buy spare parts!

How is this different from a 3-Channel Helicopter? 
A 3-Channel helicopter has a left stick which controls throttle, and a right stick which controls pitch and yaw.  There is no roll control, and pitch is extremely limited, since it is done simply via a tiny horizontal propeller near the tail which spins to create lift and slightly raise or lower the tail, thereby providing forward or aft movement.  A 3-Channel heli, therefore, is very limited in control authority, and can rarely go faster than a walking speed.  Another serious limitation is that they usually use infrared transmitters, which have a very short range, and are affected by sunlight.  Therefore, they are usually only indoor helicopters due to their ultra limited control (inability to counter even the slightest wind gusts), and infrared antennas which are susceptible to interference from the sun.  (Note: infrared transmitters are usually identifiable by a small, usually red, plastic cover near their top, instead of an antenna).

So, what is the extra channel on a 4-Channel helicopter?  
A 4-Channel helicopter, on the other hand, is highly maneuverable in comparison

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Monday, April 8, 2013

Mastering the Landing Approach, by Dave Scott

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Model Aviation magazine recently posted this article online, and I wanted to share it with the rest of you, so here is the link.  It is a good article, and many of you may find it useful in helping your landings and approaches.  The author doesn't come at the topic of landing from a completely beginner perspective, however, as it seems more tailored to helping someone improve their basic landing skills rather than develop for the first time any landing skills.  It is by a man named Dave Scott, of

Here is just one of the many diagrams from this article:

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Friday, April 5, 2013


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Written:  22 March 2013
Updated: 14 July 2013.
Note: most recent additions are at the top of this article.

I suppose I watch my fair share of videos that I find amazing or inspiring.  I am going to begin to save some of them.  I will save them at this post, so check back from time to time.

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Friday, March 1, 2013

Getting into Scratch Building - 20+ Planes with ONE Motor & ONE Power Pod!

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Getting into Scratch Building - 20+ Planes with ONE Motor & ONE Power Pod!

By:  Gabriel Staples
Written: 1 March 2013
Last Updated: 21 Feb. 2015
-added "Reinforcement" section below - 20 Feb. 2015
-added the entire "Which Foam to Buy" section, incl notes on Dollar Tree foamboard & depron - 8 Feb. 2015
-added a link to my new free-flight Stingray glider I mention below - 16 July 2013

If you have any questions or comments while reading this, or any other article, please post it in the comments section below the article.  Thanks!

Related Articles:

So, over a year ago now I discovered the Flite Test NutBall and Delta Wing (both wings, separated from the power pod, are shown in the picture above and to the right).  These planes are unique in that FliteTest came up with the ingenious idea to use a single motor, speed controller, and receiver combination in order to power multiple airplanes!  This is a fantastic solution, as it allows someone to get into this hobby VERY economically, and all of the planes are built using Dollar Tree foamboard (ADAMS Readi-board), shish kabob (bamboo) skewers, hot glue, popsicle sticks, and packing tape!

As of today, I have built and flown both the NutBall and the Delta Wing, and love them both.  I have even prototyped and tested, for my local Boy Scout troop working on the Aviation merit badge, a $5 free-flight glider based on the NutBall, which is capable of being bungee-launched (via a home-made $25~$35 launcher) to altitudes up to 250 feet, and flying several hundred yards distance in a single flight!  My wife named it the Stingray (see photo of a stingray to the right), since the glider resembles a stingray flying backwards.  I would like to post the plans and video of the Stingray glider and bungee launcher when I get the chance, so other Boy Scout troops and do-it-yourselfers can make one too (for a sneak peak of the glider, see my new post here).  As for the FliteTest airplanes I've built, the NutBall is especially a blast to fly for an advanced pilot, yet can be gentle

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Saturday, February 23, 2013

Thunder AC680/AC6 Charger & Computer Data-Logging Software

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Setting Up The Computer Data-Logging Software for Your Thunder AC680 (or AC6) Charger
~By Gabriel Staples, 24 Feb. 2013.
Updated: 3 Jan. 2014
-added a note to check out a comment below this post if you are using Windows 8
-link added for a USB extension cable.

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Brief Charger Description & Review:

Since I recommend so often to beginners in RC that they purchase the Thunder AC680 charger, I thought I better at least help them learn how to setup the computer software for it, which can be a little bit tricky, even for the computer-literate person.

First off, I'd just like to say that I love this charger, and it makes an *excellent* starter charger for someone looking to get a fully functional, computerized, smart charger capable of charging, discharging, cycling, and balancing.  This charger can handle LiPo/LiFe/Li-Ion, NiMH/NiCad, and Pb battery chemistries.  To the layperson, this means that with the right connector, it can charge any rechargeable battery in your house, car, or workshop.  That's pretty impressive.  Also, by using it to discharge a battery, you can measure the capacity (mAh) in the battery to get an idea if the battery is any good, and whether or not the manufacturer of a cheap rechargeable battery (on ebay for instance) ripped you off.  I've used a charger like this to charge and/or discharge (to check the capacity) of cell phone batteries, camera batteries, airsoft gun batteries, 18V cordless drill batteries, and dozens and dozens of various RC aircraft or radio transmitter batteries.  Lastly, by using the charger's cycling abilities, I've been able to reduce or remove the "memory" effect of many of my old NiCad batteries, and I've even been able to bring back "dead" NiCad batteries, which were over 10 years old!, to at least a usable condition after years of sitting around unused.

To top it all off, this charger is available for ~$55 with shipping from, which is a steal-of-a-deal.  Many chargers of this quality sell for 3x this much, so I have got to say, I am extremely impressed.
If you'd like to purchase this charger, you can find it at the "Thunder AC680" link above, or it is located at

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Friday, February 22, 2013

Heavy Duty Connectors and Large Gauge Wire, & XT60 Soldering Experiment

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By Gabriel Staples
Written: 22 Feb. 2013
Last Updated: 2 March 2014
-added links to full soldering tutorials

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So, tonight I decided to do an experiment to see how large of wire could be used with my favorite connector, the genuine XT60, from HobbyKing.  Ultimately, I determined that a careful hand and hot iron (60W recommended, as my "Beginner RC Airplane Setup" document explains here) can easily handle wires at least up to 7 AWG, which is a very large diameter wire.  In my experiment, I twisted two 12AWG wires together, to make a 7~8 AWG-equivalent wire, which I then soldered to an XT60 connector with no problem.  A smaller diameter wire, such as a 10 AWG, can easily be soldered to an XT60 connector with this iron linked above (as this is the exact iron I used).  However, as 10AWG wire is capable of carrying currents much greater than 60A, you may be interested in using the larger XT90 connector, on which 10 AWG wire comes standard on a HobbyKing XT90 parallel harness or serial harness.

Various Large-Current, Large-Diameter-Wire Connector Descriptions, & Links:
XT60-style connectors are my favorite, hands down, for my personal use.  The 60 means "60 Amps," so as long as your *continuous* current is 60A or less, use these connectors, with any wire up to about 7 Gauge or so (though 14AWG wire is large enough to do the trick).  Anyway, for 60A or less continuous, or ~100A peak (<=30 sec), XT60's are the way to go.  For 90A continuous, or ~140A peak, use XT90's.  For 150A continuous (250A peak), use XT150's.  Also, as a side note, 10 AWG wire is designed to easily handle a high voltage 90A continuous current over short distances (you can verify using this online calculator here, with values of 1% loss, 22.2V DC, 90A, and 0.3m cable length), but again, if your system pulls <60A continuous, feel free to use XT60's, even for wire such as 10 AWG or as large as 7AWG. 

My Soldering Experiment on the XT60 Connector:
-My goal was to see if large gauge wire (10AWG or larger) could be soldered to the XT60 connector, in order to use this connector to replace other large, bulky, or cumbersome connectors on very large battery packs where you need less than 60A continuous current draw.  (Note: if you ever replace battery connectors, be very careful not to short out the battery leads by cutting off both wires on the battery connector at once.  Rather, cut off and solder one wire at a time to a new connector).
-Results: I successfully soldered the equivalent of 7AWG wires onto an XT60 connector.  I did not try to solder wires any larger, as this was large enough for the purposes of my experiment.

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Wednesday, February 13, 2013

Building the FliteTest NutBall Swappable

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By Gabriel Staples
Written: 13 Feb 2013
Updated: 25 June 2013


--Since FliteTest has already done so much to support the build of this aircraft, it is likely that the links and pictures I already have below will suffice.  Be sure to check out my Center of Gravity section below, however, as it pertains specifically to the 24" diameter NutBall, which FliteTest does not build.  As you will see in their links below, they prefer to build their 19 1/3" version of the NutBall.

If you have any questions or comments while reading this, or any other article, please post it in the comments section below the article. Thanks!

Related Articles:
So, one of my friends I just helped get into RC was looking at my article above ("Buying Parts for the FliteTest Nutball Swappable - All at Once") the other day, and he asked me if I could post some dimensions, pictures, etc., and a few notes about how I built the airplane.  So, that's why I'm writing this post.

1st: Watch the Build Videos and Read the Flite Test Articles:
-Even watching the non-NutBall Build Videos will give you valuable building tips.  At a bare minimum, watch the Power Pod and NutBall build videos, as they both give you tips and tricks necessary to successfully build the NutBall:

  1. Power Pod Build:
  2. Power Pod Electronics install: 
  3. NutBall: 
    1. The new FliteTest NutBall build video
    2. The original FliteTest NutBall build video (I like this build video better)
  4. Delta:
  5. FT Flyer:
  6. You may also check out this article here, titled, "Swappable Nutball and Hots Dart"

2nd: Download & Assemble the Plans
-Download them, then print them, cut off the edges of the paper as necessary, and tape them all together to make full-size plans:
-I noticed that FliteTest has updated some of their plans in the articles above, so feel free to use those.  However, if you want the exact ones I have used to successfully make several NutBalls now, here they are:

All plans are available here.  To download them, click on the file you want, then go to File --> Download.
A brief description of the files is below.
(Note: I originally got the NutBall plans from page 2 of this RCGroups build thread.  The NutBall was originally made by "GoldGuy," if I'm not mistaken.  Then, FliteTest simply came along and made a swappable fuselage for it, and made it into one of their most popular planes in their "swappable series.")
  1. NutBall_full 17''.pdf - these are the 17 inch diameter plans.  I don't use these, but here they are in case you want them; I prefer the 24" diameter NutBall.  This is a one-page view.
  2. NutBall_tiled 17''.pdf - these are the 17 inch diameter plans, tiled so that you can print them out on a regular printer, cut off the excess paper, and tape them all together to get full-size plans.
  3. NutBall_24_tiled - build this one!!! (will require 2 sheets of 20'' x 30'' Dollar Tree Foam).pdf - these are the NutBall plans I use. They work great.  I prefer the 24" NutBall over the 17" of 19" NutBall, by the way, because it is still very easy to use Dollar Tree foamboard, and it has waaaay more wing area than the 17" or 19" versions, so it will have a much lower wing loading and hence be able to fly much more slowly.  It will have more of a "floaty" feel to it (which is good), than the other two versions, assuming all other things are equal.  
    -For your information, the 17", 19", and 24" diameter versions of the NutBall have wing areas of 908 in^2, 1134 in^2, and 1810 in^2, respectively.  That means that the 24" diameter NutBall has 99% more wing area than the 17" NutBall and 60% more wing area than the 19" diameter NutBall.  Again, this means it can carry much more weight and/or fly much more slowly.  
  4. swappable fuse & Delta fins (print ''poster'', 100%, w-Cut Marks, Labels, & 0.5in overlap).pdf - this file contains the swappable fuselage plans I used for my NutBall and Delta wing.  It also contains the Delta wing fins if you want them for building the swappable Delta wing plane.  Using Adobe Reader X, print as the instructions say in the file name (ie: poster, 100%.....etc).  The fuselage, firewall, and delta fins are to scale, but the landing gear is not.  It's shape is correct, but not its size.
  5. swappable delta (print ''poster'', 100%, w-Cut Marks, Labels, & 0.5in overlap).pdf - Delta plans.  here they are if you want them.

3rd: Buy the Airplane Parts:
Estimated cost of airplane only, with *no* electronics: $5~$15.
Estimated cost of optional colored packing tape (for decorating): $5~$45, depending on how many colors you buy.
Estimated cost of building supplies: $25~$40.
  1. Airframe:
    1. two $1 sheets of 20"x30" foamboard from the Dollar Tree (note: this is ADAMS brand foamboard).
    2. 1/8" plywood sheet (maybe 8"x10") from the Hobby Lobby balsa sheet rack in the back of the store ($1.79 last I checked I believe)
    3. $1~$2 pack of 100 shish-ka-bob (bamboo) skewers from Walmart (in the BBQ section of the Garden Center) or wherever
    4. Jumbo popsickle (craft) sticks at Walmart - pack of like 100 for a couple bucks - to be used to make the 2 control horns
    5. (music wire)
  2. Landing Gear (optional; note: plane is easier for a beginner to land *without* landing gear, since you can just safely belly land it *anywhere* in a large grass field, without having to worry about needing a smooth surface or accidentally flipping it over due to the wheels catching):
    1. (wheels)
    2. (Wheel Collars)
    3. (Music Wire)
  3. Building Supplies:
    1. Tape:
      1. Packing Tape:
        1. $1 roll of cheapo clear packing tape from the Dollar Tree
      2. Fiberglass-stranded Tape (mandatory item, use as the build video shows):
        1. Scotch Strapping Tape (small roll): OR
        2. Duck brand Strapping Tape: OR
        3. Scotch Extreme Packing Tape:

    2. Hot Glue Gun:
    3. X-Acto knife, box-cutter knife, razor-blade knife, or equivalent, $0.50~$8 (note to self: add link to X-blade knife & blades on HK)
    4. Precision Screwdriver set: --add link to the Husky set I have, as well as the decent Harbor Freight set.

4th: Build the Plane!
Estimated build time (this does not include electronics installation):  4.5~5.5 hrs. for the experienced builder, including electronics installation; 6~10 hrs. for the novice builder.

  • The Jumbo Popsicle Sticks are used to make control horns.  Click here for the file, then go to File --> Print.  Make sure to print the file Actual Size, NOT Shrinking it or Fitting it to a Page.
  • 1.94" high parts box, for wingtip polyhedral......follow build video

5th: Buy the Electronics

6th: Install the Electronics & Balance the Propeller

7th: Center of Gravity (C.G.), Maiden Flight, and Trimming
After much flight testing and probably hundreds of flights, here's my Center of Gravity recommendations for the 24" diameter NutBall:
Ideal CG: 5.5"~6.0" back from the leading edge of the wing, measured right along the wing root (ie: down the centerline).  The CG on this plane, however, can be about as far forward as you want (I didn't go farther forward than ~5.0"), and as far back as 6.5".  With a CG of 6.5" the plane can be very fun to fly and with large control throws does back flips (EXTREMELY tight, approx. 3 ft. diameter loops), and flat spins very well.  However, inverted flight is horrible with the CG at 6.5" back, as the plane is somewhat unstable and hence trims out with some down-elevator.  For nice inverted flight, 5.5~6.0" back works nicely.

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Saturday, February 2, 2013

This is What My NutBall Can Do!

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By Gabriel Staples
Written 3 Feb. 2013

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This is a short (very windy) flight review and verbal description of my FliteTest Swappable NutBall airplane.  It flies great, is a blast to fly, and is a solid, economical aircraft!  I made it for ~$70 or so with *everything* I needed, minus the Tx and charger.  I also used home-made jumbo pop-sickle stick control horns.  Despite its 3-channel control, it is very maneuverable and acrobatic, as the video shows, yet with small surface deflections and a reasonably-sized motor, it can also be a very docile and forgiving flyer, well suited to a beginner.  As a matter of fact, with a moderately-sized motor (120W~200W) (or using a 300W 3S motor on a 2S LiPo), and with small control throws, I'd say this airplane is a solid beginner airframe (but slightly skewed more towards the intermediate side of the beginner spectrum).
With a hot 300W high-speed setup and large control surface throws, as in this video, however, it becomes an exciting intermediate to expert airplane.  The setup in the video has a top speed of ~60mph, and in a dive, I've approached probably 80mph.  The first time I did that, however (not recorded :( ), the high speeds caused the vertical stabilizer to flutter and snap nearly off.  It folded down against the body and made a loud "snapping" sound as it slapped against the body.  I quickly slowed down and the vertical stab. popped back up part way and I made a safe landing in the grass.  A bamboo shish-kabob skewer embedded in the vertical stab, and some hot glue, fixed this problem.  
I used Dollar Tree foamboard (20" x 30") sheets, x 2, to make this airplane.

List of Recommended Beginner parts for the NutBall can be found here:


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Thursday, January 31, 2013

Buying Parts for the FliteTest NutBall Swappable - All at Once

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By Gabriel Staples
Written: 1 Feb 2013
Updated: 16 March 2014
-added warnings about using the wrong prop with the wrong motor
19 July 2014: Hey look! Hobbyking sells a small, EPP (ie: very durable foam) version of the Nutball now!  See here.

Related Articles:

So, this week I built a NutBall (see my NutBall in action here) to give to a friend turning 18.  He has no RC equipment whatsoever, and I am only giving him the airplane, with no electronics.  Here it is all ready to go (see picture ot the right).  It only took me a little over 4 hrs to put together this time, since I've done this a few times before.  It just needs the motor, battery, ESC, servos, etc.

For a good introductory-level beginner setup, for someone with absolutely no equipment, who just wants the basics, here's what I'd recommend:

Note: if any items are back-ordered (the stock status is listed at the bottom of each item on HobbyKing, to the left of the price), then you may want to do two separate orders: one with in-stock items, and the other with out-of-stock/backordered items.  This is to help speed up the shipping, as standard shipping takes 3~5 weeks from Hong Kong, and waiting for a back-ordered item can hold up your order an additional 1 week to ~2 months+ or so (backordered items usually mean about 3~4 weeks extra waiting, but this can be longer or shorter).  ( may be wondering why I don't purchase elsewhere with this type of slow shipping......well, here's my reasoning:  If you want something quickly instead of inexpensively, remove several of the items below because they are so difficult to find elsewhere, then multiply the price of the remaining items by a factor of 3 or 4, and that is the price you can expect to pay at many store-front shops).  
My recommended Order List (Electronics Only, not airplane parts and hardware) is as Follows:
  1. Transmitter (Tx) and Receiver (Rx), HobbyKing HK6S $29: - Note: one really nice feature about this transmitter is that it has a low voltage alarm which turns on at 8.5V to help you know when your transmitter battery is low.  When the red LED starts to blink, and the transmitter begins beeping, it is time to change (or charge, if applicable) the transmitter battery. 
  2. ESC:  Turnigy Plush 30A, $12:  
  3. Motor, Turnigy D2822/14 Brushless Outrunner, 1450 kv, 160W, $8:
  4. 3.5mm bullet connectors to connect ESC to motor, $2:
  5. Heat Shrink tubing (3mm, 4mm, & 5mm in red AND black), ~$2 total:  3mm red3mm black4mm red4mm black5mm red5mm black
  6. HXT900 9g servos x 3 (1 for a spare), $2.70 each x 3 = $8.10: 
  7. 3mm prop savers (will need to be drilled using 1/8" drill bit to slightly enlarge hole), $3:
  8. SF 9x6 Props (these are excellent propellers to use with the motor above and the 2S LiPo battery below; WARNING: do NOT use these props with the motor above and a 3S LiPo, as it will pull too much current and burn up the motor), $3:
  9. APC-Style Props, 7x5E (this is the ideal propeller to use with the motor above and the 3S LiPo battery below; note: though it is perfectly safe to use a 2S LiPo with this prop, and the plane still flies fine, it will have reduced power and speed when using this prop with a 2S LiPo; therefore, if you want better power, use one of the larger props in this list when using the above motor with a 2S LiPo), $2,
  10. APC-Style Props, 8x6E x 2, $1 each x 2 = $2 (these are also good with the above motor and a 2S LiPo; WARNING: do NOT use these props with the motor above and a 3S LiPo, as it will pull too much current and burn up the motor),
  11. 2S LiPo Battery, 1300mAh x 2 or more (for lower-speed flight), $8 each x 2 = $16:
  12. 3S LiPo Battery, 1300mAh x 2 or more (for higher-speed flight), $9 each x 2 = $18:
  13. XT60 connectors x 1 pack, ~$3.50,
  14. Battery Voltage Checker, $10: and/or this one, with beeper (to notify you when your battery is low, so you can land), $4: 
  15. Cheap Charger & Power Supply, $11:  
  16. LiPo-Safe Charge Bag, $3:
  17. Velcro, $2.50 (this stuff is better than anything in a local store, and 1/3 the price, so I really recommend it--a mandatory item to secure your batteries to the plane): 
  18. Quick connectors/EZ connectors for push-rods, $1.50,
Item Total: ~$149
Guestimated Shipping, based on past experience: ~$35'ish
Order Total: ~$185

My recommended Order List (for Airplane Parts, Tools and Hardware is as Follows: 
  1. Dollar Tree foamboard, $1/sheet x 2 sheets = $2 for the 24" NutBall version (get plans for it on my post here).
  2. bamboo skewers (ie: Shish Kabob skewers), 12" long, 1 pack of 100 or so, $1~$2 at your local store
  3. 2mm (0.078") diameter music wire, for the landing gear, ~$3.50 at your local RC hobby shop or toy train store, or ~$10 (with shipping) on Amazon here
  4. 1.19mm (0.047") diameter music wire, for the control rods, ~$3 at your local RC hobby shop or toy train store, or $8.33 (with shipping) on Amazon here
  5. control horns, $0.50,; or, as I prefer, build your own from jumbo Popsicle craft sticks (see here, under the 4th section, called "Build the Plane").  
  6. 50mm wheels, $3,
  7. 2.1mm wheel collars, $2, 
  8. X-blade knife, $1,
  9. extra X-blades, $1/pack x 3 packs or so = $3,
  10. simple prop balancer, $1.50, (I have this nice one, if you want it instead, $20:
    1. Having a well-balance prop can potentially make a huge difference in minimizing vibration and power losses and prolonging your equipment life.
    2. For propeller-balancing instructions, techniques, and tips, read the Top Flite Power Point Propeller Balancer manual, pgs. 3-6, here: Of the three methods described in the manual, I prefer "method 2" (using super glue and accelerator to add weight to the back side of the light blade on the propeller).
  11. super glue, medium viscosity, with clog-free cap, $2.50 (I love these caps, and this glue is 1/3 the price as you'll find elsewhere):
  12. super glue accelerator, $5 (this stuff allows the super glue to cure instantly, and is necessary in order to balance a propeller),
Item Total: ~$30
Guestimated Shipping for the HobbyKing portion of the order, ~$12
Order Total: ~$42

Grand Total: $185+$42 = $227
Note: this may seem like a lot, but REMEMBER:  most of this equipment is support equipment you have to buy ONE TIME (ex: batteries, charger, glue, radio transmitter, battery voltage checker), or parts that come in bags with enough pieces for 2~4+ planes (ex: prop savers, wheel collars, music wire, control horns, velcro, bamboo skewers).  Not only that, but the power pod is swappable!  THEREFORE, THE COST OF YOUR NEXT PLANE WILL ONLY BE ABOUT $15~$20, OR LESS, IF YOU USE THE SAME SWAPPABLE POWER POD but buy new servos, OR ~$70~$80 if you buy a new motor, speed controller, battery, and receiver.  See how cheap this can be once you get started!?

Miscellaneous Extras to buy locally:
  1. Clear Packing Tape at Walmart or wherever else you choose to buy it. – good for repairs where the full stickiness and strength of strapping tape is not needed.
  2. Scotch strapping tape at Walmart, Meijer, or wherever else you choose (strapping tape has fiberglass strands running down it), or on Amazon here for only $5.09!
  3.  ***Dual temperature*** Hot Glue gun and glue, ~$15 (with glue sticks) from Walmart.  “Dual temperature” means that the glue gun MUST have dual heat settings, high/low so that you can use low setting when you need to and not melt the foam plane, yet you still have high to help it heat up faster and get more sticky on surfaces that can handle a little more heat (hotter = more sticky). You can also buy a good one of these glue guns from Amazon here: <-- Note: I own this exact glue gun and it works well. It works fantastic for RC planes and has a nice, precision tip and hasn’t broken on me with regular use in the past 4 years I’ve had it. If the glue ever gets jammed (has happened a few times after being on high heat for very long periods of time), pull the glue stick out, pull off the melted portion that may be getting stuck in the gun, re-insert glue stick, and continue use.  I use the “high” heat setting to heat it up quickly, then I switch to “low” once it’s hot so I don’t melt the foam.  About 1 minute before each use, I switch back to "high" to get the glue sticky and easier to squeeze out, then during use I switch back to "low" so it doesn't get too hot.  This process can take some practice, but ultimately you know the glue is hot enough when it is hot enough to burn you if you don't roll it off your fingers, but cool enough to *not* burn you if you *do* roll it off your fingers.  You're smart, figure it out. :)  So far that I have found, the quality can’t be beat for its price, though better dual temperature glue guns do exist.
  4. 8 AA batteries for the transmitter

Please leave your comment below:  So, would you recommend this list of parts for a NutBall to a friend?  Why, or why not?

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Sunday, January 27, 2013

Calculations For Additional Capacitors Necessary in a certain 21-motor Airplane Setup

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These are my calcs, in regards to Posts 540~543 (here: and here  Basically, I tried to figure out how many additional capacitors are necessary on each of the 21 ESCs in order to offset the voltage ripples caused by increased battery lead length (which can destroy/damage the existing capacitors in your ESC if you don't add capacitors to help absorb the magnetically-induced voltage spikes [refer to post 1 in the above thread for more info about this]).

I am only putting this spreadsheet here because RCGroups won't allow it as an attachment on their website.
To download the file, click here then go to File --> Download:
The above link is to the old spreadsheet.  I have corrected some errors, and the NEW SPREADSHEET LINK IS FARTHER BELOW!

Update: 20 March 2013 - Spreadsheet corrected and now available here (go to File --> Download to save):

Update notes:  I added the "Total Capacitance Needed" (Row 25 in the new spreadsheet) in the calculations, and I removed the row called "Additional Length, beyond ESC's design, for which you must add Caps (in.)" (Row 22 in the old spreadsheet).  I then added Row 26 as well, and corrected the formulas in Row 27.  This allowed me to account for the additional current in the entire wire station length, not just in the length beyond that of what the ESC was intended to handle (Cell Q14) at its max rated continuous current (Cell Q11).

Here is a table of the differences in end-results between the old and new spreadsheets, for this one particular example:

For jaccies (referring to Post #579 here)
Download spreadsheet here (go to File --> Download to save)

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Tuesday, January 22, 2013

Parallel Charging Your LiPo Batteries

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Parallel Charging Your LiPo Batteries
By Gabriel Staples
Initially written 12 April 2011
Preface & explanations added on 22 Jan. 2013
Most Recent Update: 26 Feb 2017

-added a lot of notes about fuse-protected parallel charge boards - 21 July 2015
-added a couple more things to list of Do's & Don'ts, & clarified "But what about cell balance..." section; added another rule about battery chemistry - 5 May 2013

Why Use Parallel Charging?
I use a Triton 2 EQ 100W balance charger ( [Note: I don’t really recommend this charger, I just bought it before I knew much about chargers.  This thing is ridiculously expensive for what it does and has some silly quirks, occasional bugs, and outdated firmware]) to regularly charge up to 8 2S 500-1000 mAh packs simultaneously, all in just over 1 hour! I also regularly charge 3S LiPos and micro 1S Lipos (I’ve done up to 14 of those at once) simultaneously using that one, single-port charger. This is called parallel charging. Essentially, parallel charging allows you to plug in many batteries at once, into one port in a single charger, and, if your charger is powerful enough, charge them all in ~1 hour or less.  All at once—boom, done!  No more messing around buying many chargers or setting up the charger many times to charge multiple batteries.  I use this charge board (shown above) plus a couple other parallel adapters I plug into it.  If you use Deans connectors, use this board instead.  The board by itself is designed for only up to 6 batteries at once, so I added a couple parallel harnesses to get 8. However, YOU MUST KNOW WHAT YOU ARE DOING OR PARALLEL CHARGING IS DANGEROUS. For example, if you plug a 2S battery in with a 3S battery, the 2S battery will be destroyed and catch fire if you leave it there.

One thing that annoys me very much about virtually all local hobby shops is that as of today, 22 Jan 2013, I haven’t found a single one that uses parallel charging or sells parallel charging equipment yet, and yet I’ve been into about 12 local shops in the past few years and looked specifically for parallel charge equipment.  This charging technique has been around for probably 6 years, and is very effective and safe when done right, so I have to assume that most local hobby shops are either A) completely oblivious about parallel charging, B) do not want to promote it because it is better for them to sell another charger rather than a parallel charge board (ie: they’ll make more money selling another charger), or C) they secretly use this technique at home but simply don’t want to be responsible for user error if a customer destroys their equipment or property if they don’t know what they’re doing while attempting it.

UPDATE (21 July 2015): I have found a hobby shop that now has parallel charging equipment! It is Radical RC. (They've had them for a couple years now, I just haven't updated this article until now). Way to go Radical RC!

(photo below: parallel charging in progress--6 2S LiFe batteries plugged into a parallel charge board
[photo source:])

Despite this, I am a strong proponent of parallel charging and have used it nearly every charge I’ve ever done since I discovered it in the early part of 2011.  I am always recommending to people that they use parallel charging, as it allows any single port LiPo charger to charge many batteries at once instead of just one battery at once.  With the right harness, even a cheap $5 2-3S LiPo charger can do parallel charging!  (However, this is less useful since these low-power chargers don’t have enough power to maintain a 1C charge rate anyway).  So, let’s get started. 

First off, parallel charging can be done with LiPo, LiFe, or Li-Ion batteries ONLY.  Do NOT attempt to use this technique with NiCad/NiMH batteries, etc., as they use a peak voltage (ΔV) detection charge technique rather than a constant current/constant voltage (CC/CV) charge technique.  A battery chemistry capable of being charged via the CC/CV technique is a must for parallel charging to be safe and effective. 

What is parallel charging?
Parallel charging means that you plug many LiPo batteries into each other via a special board or harness so that all of their negative leads are connected to each other, and all of their positive leads are connected to each other.  Now, the entire battery packs are in parallel.  In order to balance the cells with your charger, however, the balance wires of all of the batteries must also all be connected in order to put the individual cells in parallel with each other.  WARNING: YOU CAN ONLY PARALLEL CHARGE BATTERIES OF THE SAME CELL COUNT (or the lower cell count battery will catch fire), AND SIMILAR STATE OF CHARGE (or damage to the lesser-charged battery will occur).  When many batteries are connected in parallel, the charger “sees” all of them as a single, large battery, with a capacity equivalent to the sum of their individual capacities. 

But what about cell balance—how does parallel charging really work?
In nature, whenever a gradient exists, a natural balancing process will occur.  A gradient means that there is a high concentration of something as compared to a low concentration of that same thing near it.  For example, if you pour salt into still water, the area of water where the salt is will become very salty.  The rest of the water lacks salt, so this “salt gradient” will naturally cause the high concentration of salt to balance out, or diffuse, into the water with a low concentration of salt.  The same occurs with heat.  Heat will naturally diffuse from a hot area into a cold area, attempting to find a balance.  If the hot area always remains hotter than the colder area, it is not because the heat isn’t diffusing, but rather it is because a heat source exists at the hot spot, and there is a resistance to the heat flow preventing it from fully diffusing.  Pressure also follows this natural balancing process.  Take a blown up balloon, for example, and untie it.  There is a large pressure difference (or gradient) between the air in the balloon, and the air in the room.  The high-pressure air in the balloon will rush out into the lower-pressure air in the room, diffusing the high pressure into the lower pressure until an equilibrium pressure is achieved.  Electricity also follows this principle of diffusion.  The battery with the higher voltage will naturally push its charge (electrons) into the batteries with lower voltage, when plugged in parallel, until all batteries equalize to the same voltage.  Since the individual cells of each battery are also in parallel with the individual cells of all the rest of the batteries, when the balance leads are connected in parallel (by plugging them all into a parallel charge board), all of the strings of cells in parallel will also equalize to the same voltage.  Now, when you plug the entire parallel charge board balance lead into your charger, your charger will balance out the cells of each battery as if it was simply one large battery.  The charger will "see" the first string of cells in parallel as a single "Cell 1," and the second string of cells in parallel as a single "Cell 2," and the third string of cells in parallel as a single "Cell 3," etc., balancing them as if they were individual cells of a larger capacity battery!  The result is that in parallel charging, all cells come out properly balanced so long as the cells are not damaged, your charger is functioning properly, you plugged them all in properly, and nothing else is wrong!

Update Notes [21 July 2015]
Fuse-Protected Parallel Charge Boards: 
This entire article is written for those of you using raw, unprotected parallel charge boards with NO fuses or current protection circuits of any kind. If anyone tells you that you *must* have protection power fuses and polyfuses and things on your board, they are flat out wrong. I don't own such a board. I still use the raw, unprotected boards. IF YOU FOLLOW MY PROCEDURES THIS IS PERFECTLY FINE AND SAFE. If you make a mistake, however, a fuse-protected board could prevent a battery mishap, so feel free to buy protected boards. 

IN THE PAST FEW YEARS, as parallel charging has become more widespread, companies selling parallel charge equipment have added things such as large power fuses to the main leads, and small polyfuses (self-resetting, automatic fuses), to the balance leads. You can recognize these well-protected and more advanced boards usually by their price tag. They are oftentimes very expensive! (Think: "I could buy another cheap smart charger, or I could buy a parallel charge board" kind of expensive). 

Here's how a fuse-protected parallel charge board might work/save your butt:
  • If you are foolish or inattentive and plug a fully-charged battery into an empty battery, for instance, the main fuse will blow. You'll have to replace it. It may be an automotive-type fuse you can buy at an auto parts store. If you make this mistake on an unprotected board, this large current may damage the main leads, blow the large traces in the parallel charge board, and damage the lower-charged battery, causing it to puff up or even catch fire.
    • Note: the main fuse requires a *lot* of current to blow usually, so, you better still follow my guidelines below to keep you and your batteries safe.
  • If the batteries are too far out of balance, or if you plug the balance leads in parallel first, before the main leads, an unsafe surge might go through the balance leads. A polyfused parallel charge board will automatically limit this current flow through the balance leads, preventing any problems. The polyfuses will simply close off (passively, but automatically increasing their resistance) to limit the current flow. If you make this mistake on an unprotected board, this large current may heat up and melt, damage, or blow the balance leads, blow the balance traces in the parallel charge board (I've done this by touching the balance leads to the balance board backwards, in reverse polarity, for instance), or cause a high enough current to the lower-charged battery to damage it. 
  • The same goes for reverse-polarity protection: a protected board may protect against this mistake. An unprotected board.....could cause the same problems as above. You might experience damage to the leads, blowing traces in the board, batteries on fire (if the reverse-polarity contact is prolonged), spark-welding of plugs together, etc. 
Summary of the above: I like the raw, unprotected boards. They work well for me. They are very inexpensive. They are easy to find, and parallel charge harnesses can be easily hand-made if desired. If you follow my rules below, unprotected boards work fine. If you are prone to errors or want extra protection, consider buying the protected boards with things like main lead fuses, balance lead polyfuses, and reverse-polarity protection.

The Do’s and Don’ts of Parallel Charging/A Couple Things to Know About Parallel Charging:

General Rules of Thumb (again, these rules work perfectly well for normal, unprotected [without fuses] parallel charge boards, and they work great for fuse-protected boards as well!):
  2. ONLY PARALLEL CHARGE BATTERIES OF THE SAME LITHIUM CHEMISTRY TYPE TOGETHER.  Ex: LiPo with LiPo, LiFe with LiFe, Li-Ion with Li-Ion, but NOT LiPo with LiFe, LiPo with Li-Ion, etc.
  3. Preferably, use batteries of similar capacities. Ex: 500~1500 mah batteries together, or 1000~2200 mah batteries together, but not a 500 mah battery with a 10,000 mah battery.
  4. Use batteries with similar states of charge (how much they are charged/discharged). Ex: do NOT put a 1/2 full or 3/4 full battery in parallel with an empty battery. All batteries must be at similar discharge state.  SEE PLOTS BELOW FOR MORE INFORMATION.
  5. Use batteries of similar ages. Ex: it is not as advisable to put a new battery with a 2 year old battery, but not critical as long as the batteries are similar capacities (mAh ratings), the same cell count, and at similar discharge states.
  6. Always plug in the *main* plug first on ALL batteries, *then* plug in all the balance plugs.  Also, it is good to *wait several minutes* AFTER plugging in the main battery leads into the parallel charge board BEFORE plugging in the balance plugs. This prevents high currents from flowing through the balance plugs as the batteries equalize based on their varying voltages upon plugging them in. The main plugs can take more current. This is also the reason you want to use batteries of similar states of charge/discharge.
    1. Fuse-protected parallel charge board note: this rule of plugging in the main leads, waiting a while, *then* plugging in the balance leads always works if you also follow all of the rest of my advice, *even with fuse-protected boards.* However, people have told me that some polyfuse-protected parallel charge boards recommend you plug in the *balance* leads first, wait a while, *then* plug in the main leads. Why? Well, it seems logical to me that this is because the balance leads are polyfuse protected. Since the balance leads have polyfuses, they act as automatic current limiters to let the charge between the LiPos more slowly balance out. The main leads require too much current to be easily polyfuse-protected, however, so the balance leads are probably the ones with the current-limiting polyfuses. So...if your particular "protected board" recommends this "reversed plug-in order," that's ok. You may choose to follow their advice, depending on how well-designed their board is, or you can just follow my standard advice and order. I like to just stick to all of my standard rules here, because I know they always work, for all boards, whether fuse-protected or not, all of the time. 
  7. Be VERY CAREFUL to plug in the main leads and balance leads correctly.  Attempting to plug them in backwards will cause a short circuit and a spark, and potentially damage your batteries and/or your parallel charge board or battery leads.  (Note: many parallel charge boards require the balance plugs to be in a certain orientation on one side of the board, and in a reverse orientation on the other side of the board, so pay careful attention to the plastic guides on the plugs to ensure you attempt to plug in the balance leads correctly.)
  8. Once all batteries are plugged in together in parallel, wait several minutes (3~10 minutes or so) for them to equalize their voltages.  The farther apart the batteries' charge states, the longer you should wait.  See plots below.
  9. To determine the charge rate when charging in parallel (assuming the standard 1C charge rate), ADD all of the battery capacities together, then use that value as the charge current. Ex: parallel charging three 3S 1300 mAh (1.3Ah) LiPo's with two 3S 1000 mAh (1Ah) Lipo's would mean that you should set your charger on the 3 cell LiPo setting at a charge rate of (3 x 1.3) + (2 x 1) = 5.9A. Therefore, in this scenario, a charge rate of 5.9A corresponds to a 1C charge rate, and the charger will consider all of those batteries in parallel to be a *single* 5900 mAh (5.9Ah) 3S Lipo.
  10. It is recommended to use a fire-proof LiPo-Safe Charge bag when charging, such as this one here.  I like to place the entire charge board with all of the attached batteries, if possible, inside of the same charge bag.  If the batteries are very large, and this is not possible, feel free to separate the batteries into separate charge bags.  Note: charge bags have a special slit in the side, near the velcro, to allow the cables to come out of the bag, so placing the entire charge board, or individual attached batteries, into a charge bag is not a problem.
Feel free to Google for more info on "parallel charging" of LiPo packs. Again: this method is NOT recommended for NiMh or NiCad cells, as it may cause them to catch fire, though for LiPos it works great!

Also see these links as additional sources:

To purchase parallel charging equipment:
I recommend HobbyKing (, ProgressiveRC (, or BuddyRC (

Parallel charging all these batteries at once with only 3 chargers!
[photo source:]

Useful Plots:
And is only an ***approximation***

Parallel Charging Note: 
AS LONG AS THE BATTERIES ARE WITHIN ~25% (OR LESS) STATE OF CHARGE OF EACH OTHER, THEY MAY BE PARALLEL-CHARGED TOGETHER.   If they are more than ~25% apart, the higher-charged battery will push a current into the lower-charged battery equal to or greater than a 1~2C charge current, which is bad. 
(To know for sure how much current the higher-charged battery is pushing into the lower-charged battery, and to see when they are nearly equalized, I like to hook up a power meter in between the parallel charge board and the *lowest-charged* battery, then I plug the remaining batteries into the parallel charge board, one at a time, beginning with the one that is least-charged and plugging in the one that is most-charged last.)

Also, after plugging in all main battery leads in parallel to each other, it is best to let the batteries’ voltage equalize for a few minutes before plugging in the balance leads in parallel and beginning the charge.  The chart below is just a rough estimate of how much time is recommended to let the batteries equalize their voltages prior to plugging in their balance leads and starting the charger.  Note: State of charge range = most charged battery State of Charge – least charged battery state of charge.  Ex:  If the most full battery is at 50% and the least full battery is at 30%, the state of charge range is 50% - 30% = 20%. 

For additional general LiPo information:
See my extensive article I wrote, titled “The Details of Electric Radio Controlled Aircraft,” under the “Battery” section of the document (approximately pgs. 22-35), found at my other website here:

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