Buying Parts for the FliteTest NutBall Swappable - All at Once

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:

• Building the FliteTest NutBall Swappable - this post includes info. about where the C.G. should be on the 24" NutBall
• This is What My NutBall Can Do!
• Getting into Scratch Building - 20+ Planes with ONE Motor & ONE Power Pod!
• Beginner RC Airplane Setup

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).  (So....you 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: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=16239&aff=281904 - 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: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=2164&aff=281904  
3. Motor, Turnigy D2822/14 Brushless Outrunner, 1450 kv, 160W, $8: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=12916&aff=281904
4. 3.5mm bullet connectors to connect ESC to motor, $2:   http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=68&aff=281904
5. Heat Shrink tubing (3mm, 4mm, & 5mm in red AND black), ~$2 total:  3mm red, 3mm black; 4mm red, 4mm black; 5mm red, 5mm black
6. HXT900 9g servos x 3 (1 for a spare), $2.70 each x 3 = $8.10: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=662&aff=281904 
7. 3mm prop savers (will need to be drilled using 1/8" drill bit to slightly enlarge hole), $3: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8240&aff=281904
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:  http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=9846&aff=281904
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, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=22424&aff=281904
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), http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=5438&aff=281904
11. 2S LiPo Battery, 1300mAh x 2 or more (for lower-speed flight), $8 each x 2 = $16:  http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=11902&aff=281904
12. 3S LiPo Battery, 1300mAh x 2 or more (for higher-speed flight), $9 each x 2 = $18: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=11903&aff=281904
13. XT60 connectors x 1 pack, ~$3.50, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=9572&aff=281904
14. Battery Voltage Checker, $10: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=19946&aff=281904 and/or this one, with beeper (to notify you when your battery is low, so you can land), $4: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=18588&aff=281904 
15. Cheap Charger & Power Supply, $11:  http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8247&aff=281904  
16. LiPo-Safe Charge Bag, $3: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=4364&aff=281904
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): http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=9374&aff=281904 
18. Quick connectors/EZ connectors for push-rods, $1.50, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8519&aff=281904

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, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8235&aff=281904; 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, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=10404&aff=281904
7. 2.1mm wheel collars, $2, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8408&aff=281904 
8. X-blade knife, $1, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=9332&aff=281904
9. extra X-blades, $1/pack x 3 packs or so = $3, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=9333&aff=281904
10. simple prop balancer, $1.50, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=14927&aff=281904 (I have this nice one, if you want it instead, $20:  http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXHY61&P=ML)
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:  http://manuals.hobbico.com/top/topq5700-manual.pdf. 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): http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=7173&aff=281904
12. super glue accelerator, $5 (this stuff allows the super glue to cure instantly, and is necessary in order to balance a propeller), http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8456&aff=281904

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:  http://www.amazon.com/Adhesive-Technologies-0443-Two-Temp-Cordless/dp/B001689XCQ <-- 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?

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

These are my calcs, in regards to Posts 540~543 (here: http://www.rcgroups.com/forums/showthread.php?t=952523&page=36 and here http://www.rcgroups.com/forums/showthread.php?t=952523&page=37).  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:  https://docs.google.com/file/d/0BwHItOaHOOvdeFQ3WTd2T1Q5Y2s/edit.
The above link is to the old spreadsheet.  I have corrected some errors, and the NEW SPREADSHEET LINK IS FARTHER BELOW!

FOR NEW SPREADSHEET, CLICK LINK BELOW
Update: 20 March 2013 - Spreadsheet corrected and now available here (go to File --> Download to save):  https://docs.google.com/file/d/0BwHItOaHOOvdQmp3c3gydzV3SU0/edit

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)

Parallel Charging Your LiPo Batteries

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Other Articles You May Be Interested in Reading:

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• Thunder AC680/AC6 Charger & Computer Data-Logging Software
• Getting into Scratch Building - 20+ Planes with ONE Motor & ONE Power Pod!
• This is What My NutBall Can Do!
• Buying Parts for the FliteTest NutBall Swappable - All at Once

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Don't forget to like, share, and subscribe using the links at the right.  ~eRCaGuy

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This article is also posted on FliteTest.com here:  http://flitetest.com/articles/Parallel_Charging_Your_LiPo_Batteries 

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

Update History (newest on top):
-added a YouTube video demonstrating "How to Use a Power Meter to Safety put 10 x 3S LiPo Batteries in Parallel for Charging" - 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 (http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXVZA8&P=ML [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.

Background:

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: http://www.buddyrc.com/])

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!

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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!):

1. ONLY USE LIPO/LIFE/LI-ION BATTERIES WITH THE SAME CELL COUNT, ***NO*** EXCEPTIONS. Ex: 2S with 2S, 3S with 3S, etc.
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:

***** https://sites.google.com/site/tjinguytech/charging-how-tos/parallel-charging

***** http://www.rchelicopterfun.com/parallel-lipo-charging.html

**** http://www.rcgroups.com/forums/showthread.php?t=932319

To purchase parallel charging equipment:

I recommend HobbyKing (www.hobbyking.com), ProgressiveRC (http://www.progressiverc.com/), or BuddyRC (www.buddyrc.com).

HobbyKing Parallel Charge Boards/Squid Harnesses:
-     http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=14856&aff=281904
-     http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=24230&aff=281904
-     http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=14852&aff=281904
-     http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=10621&aff=281904
-     etc.....You get the idea.  Main link to their charging cables is here:  http://www.hobbyking.com/hobbyking/store/uh_listCategoriesAndProducts.asp?idCategory=410

ProgressiveRC Parallel Charging Equipment:
-     http://www.progressiverc.com/adapter-cables-and-boards/parallel-boards
-     http://www.progressiverc.com/adapter-cables-and-boards/charge-cables/parallel-charge
-     http://www.progressiverc.com/adapter-cables-and-boards/balance-cables

BuddyRC Parallel Charging Equipment:
-     http://www.buddyrc.com/paraboard-parallel-charge-board.html
-     http://www.buddyrc.com/accessory/parallel-charge-cables.html
-     http://www.buddyrc.com/accessory/balance-cables.html?limit=all

Parallel charging all these batteries at once with only 3 chargers!
[photo source: http://www.rchelicopterfun.com/parallel-lipo-charging.html]

Useful Plots:

PLOT IS FOR LIPO BATTERIES ONLY,

And is only an ***approximation***

(Source:  http://www.rcgroups.com/forums/showpost.php?p=6660057&postcount=7)

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:  https://sites.google.com/site/electricrcaircraftguru/.

Buying Parts for the FliteTest NutBall Swappable - a little at a time - Stage #1

Related Articles:

• This is What My NutBall Can Do!
• Buying Parts for the FliteTest NutBall Swappable - All at Once
• Building the Flite Test NutBall Swappable
• Getting into Scratch Building - 20+ Planes with ONE Motor & ONE Power Pod!

----------------------------------------------------
I have a friend who wants to know which parts to purchase for the FliteTest Nutball (http://flitetest.com/articles/nutball_scratch_build), as his very first plane.  He owns absolutely no RC vehicles or components whatsoever, so this truly is his "beginner plane setup."  Several months ago I started helping him build it.  However, due to budget constraints, he has never gone through with the build to finish it up.  So, I am going to split up the electronics/extra components he needs into several low-cost (~$30 each) "stages" in order to see if he can do it this way---a little at a time.  Let's see how this goes....

This is the $35 (-ish) Stage #1 (of approximately 4 total):  I'll try to put the parts roughly into a recommended purchase order, according to what is needed first to complete the plane.

What he already has:

1. two $1 sheets of 20"x30" foamboard from the Dollar Tree.
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 roll of cheapo clear packing tape from the Dollar Tree
4. $1~$2 pack of 100 shish-ka-bob (bamboo) skewers from Walmart (in the BBQ section of the Garden Center) or wherever
5. Jumbo popsickle (craft) sticks at Walmart - pack of like 100 for a couple bucks - to be used to make the 2 control horns

Ok: Stage #1 - buy this week

1. "Music Wire" (0.047 in. [1.19 mm] diam. From local hobbyshop) (sizes as small as 0.032 in. [0.81 mm] also work, but the 0.047 in. is better). Cost: $2.29 for a pack of 4 long (36" maybe) rods. - will be used for the two control rods.
2. Scotch Strapping tape (has fiberglass strands running down it) from Walmart or wherever, ~$3
3. HobbyKing order:
1. motor: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=12916&aff=281904, $8
2. HXT900 9g servos x 3 (1 for a spare), $2.70 each: http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=662&aff=281904 
3. XT60 connectors x 1 pack, ~$3.50, http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=9572&aff=281904
4. Shipping: ~$6
5. TOTAL PRICE WITH SHIPPING:  ~$26.
4. Stage 1 total:  ~$31.50

Bonus Bomb Drop

-Building a Bomb Drop can be *very* simple, fun, and cheap, but you'll need a few extra parts in your HobbyKing order.  Here's the Bomb Drop Video by Josh and Josh of Flite Test.  And here's a picture of it to the right.  What you will need to purchase is very simple:

1) Extra HXT900 Servo
2) Servo Extensions (to get the bomb drop servo wire to be long enough to reach the receiver)
3) Servo Wire Splitter (Y-harness).  Note:  If you have a 5 or more Channel Radio, all you need are items 1 and 2, but if you have only a 4 Channel Radio (like what comes with the Bixler V1.1), then you will also need this item.  In the case of using your bomb drop on a 4-channel radio, the splitter will be used to send the rudder signal to both your rudder servo, as well as your bomb drop servo.  That way, you activate your bomb drop by moving the rudder.  This is ok since you don't need to use the rudder much during flight anyway, but it's still available if you need it, once you drop your bomb.