I’m building a Hexapod on the side while I’m working on a few projects. I have about half the brackets laying around that I need. Before I order a bunch I thought I’d ask if anyone has some extra servo mounts and long or short C brackets, shoot me a PM. Preferably the brushed ones.
I’m also looking for flange bearings. The ones that come with the C brackets. And plastic or aluminum round Hitec servo horns.
I can pay by Money Order or I have loads of R/c stuff to trade.
I have over 50 Lipo packs and loose cells. Ranging from 250 mAh to 12,000 mAh.
I have loads of 4000mAh 4K Sub-C cell NiMh packs from 6 to 32 cells. I also have loose cells.
Bulk servo wire, 5 to 120 Amp Castle Creations ESC’s, Mega Brushless motors 400 and 600 sized, Johnson 680 and 600 brushed motors, Wireless 2.4GHZ color camera with receiver and lots more.
If you need anything battery related I build customs packs in AA, AAA, sub-C and Lipo. Any size, arrangement, capacity, discharge and voltage. I have custom fan cooled Sub-C packs as well. I also custom fabricate Fiberglass, Plastic, Kevlar and Carbon fiber parts. I can do Castings, sheet, milled or low-pressure injection.
wow, that sure is a lot of stuff, but im curious, if we paid you enouigh money, would you be willing to do these things for us without trading you brackets?
I don’t see why not. I’ve built alot of packs for R/s planes, helis and trucks for fellow hobbyists. The fabricating is something I’ve been getting into for some time now. I slowly started buying and building my own tools and equipment and learning the fabricating through trial and error over the years. I hope to eventually go into full production on some of my designs.
Don’t worry Jim, none of them are even close to your products. Totally different area.
Were you referring to the battery packs or the fabricating? I do custom work for both by request. The time frame would depend on the project, materials used (if I have them in stock), and scale. If you just need a simple battery pack made up, I can do that in about 10 minutes so long as I have the cells you want. I do the batteries strictly as a personal favor, it is seperate from my business matters. So I will not produce large quantity orders or repeat orders that lead me to believe someone is reselling them.
Just let me know what you are looking for and if I can’t help you, I can probably refer you to some suppliers.
Does this mean you don’t have any SES brackets for me.
Most people here can’t get enough SES brackets, so you’ll probably need to order. However, a lot of people (myself included) would probably be interested in buying a few of the LiPo packs or other items. This money could then be applied to getting brackets…
I’m wondering what kind of capacity to weight ratio you get? A 10,000 mAh pack should be able to power a good sized bot and a small ITX computer to give it a brain. Some of my first posts were talking about possibly buying some LiPo cells and/or packs, but I know very little about them except that they can be dangerous if you don’t know what you’re doing, so I decided to presue other areas and only come back once I really needed such a power system.
Well I run a 12,000 mAh 20C 14.8 Volt lipo in one of my helicopters.
The pack can take 240 Amps constant and 600 amps in 3 second bursts.
The pack costs me around $300 in cells and shrink. And would retail for $400 to $450 dollars. The finished pack weights exactly 35.34 oz or 2.2lbs (1002 g).
I also have a 32 cell pack of IB Intellect 4200 mAh sub-c cells for an aerobatic plane. It weight 84.8 oz or 5.3 pounds.
I could arrange 36 cells into a higher percentage of parallel groups (like 3 groups of 12 cell packs in parallel)and be at 14.4 Volts at 12,000 mAh. The pack would weight just over 90 oz.
Although the IB4200 is one of the best sub-c cells available, they will get pretty hot at anything over 10C. So you are looking at a 120 amp continuous discharge and could probably go with 180 to 200 amp bursts for 5 to 10 seconds.
So:
**Battery: Lipo **
Capacity 12,000 mAh
Voltage 14.8 V
Discharge 20C (240 Amps)
Weight 2.2 lbs
Size 6X4X4
Price $400
Battery: NiMh
Capacity 12,000 mAh
Voltage 14.4 V
Discharge 10C (120 Amps)
Weight 5.4 lbs
Size 10X6X6
Price $320
So lipos have a huge discharge and weight advantage. But you pay for it.
Now the real reason why everyone doesn’t get into huge lipos right off the bat. Some people don’t realize this until they have bought their $400 pack.
You can arrange your 36 cell NiMh pack into 12 cell packs and buy 3 cheap $40 chargers. One for each pack so you can charge all three sections at once. Or buy a charger capable of charging a 12,000mah 36 cell pack. But that’s around $400.
Now you say lipos are so light and amazing, why not buy that lipo pack for only a hundred bucks more? Because almost every lipo charger out there charges a max of 3 to 4 cells. Which is ok. We are running a 4 cell pack. But all those chargers also only charge up to a 3000 or 5000 or even 9000 mAh pack. So you need to find one that can do 12,000. Now you have to buy your $400 computer charger. Or buy 2 $150 chargers that can do 6000 mAh each and build your lipo pack into 2 X 6000 mAh packs with a Parallel Y harness so you can split it to charge it.
So getting into big lipos is expensive but staying in it is worth every penny. Once the initial investment is made, you will never go back. I guarantee it.
If it’s smaller packs (under 5000 mAh and under 28 volts) the packs can be made much cheaper than retail and you can pick up alot of different chargers nowadays for $20 to $300 that will do these packs.
There is a wealth of other factors and options but as you can see, I’m rambling now.
That answers my initial question completely, you definately know your stuff. I think the immediate answer is its still to expensive for me to do this just yet. Sorry.
2.2 lbs for 12,000 mAh @ 14.4V is truely amazing though. I honestly only need half the volatge, since I found a nice ITX power supply that works best (90+ efficiency depending on boards, etc.) at lower voltages and I doubt my servos would be happy at much over 7.0V either and running a regulator for servos is somewhat wasteful.
Just for my own knowledge could this 12,000 mAh @ 7.2V be made at 1.1 lbs or do the cells just not devide that way? If it is, I’ll probably be asking more questions and/ or making an order sometime in the futue.
I think the thigh that really does it for me is the chargers. I have a LN-5014 which can do 5 LiPo cells (18V), just caps the max capacity at 5000 mAh, meaning even for a dual charger method its useless. I just can’t justify a $600-800 investiment at this point for something I don’t really *need * yet.
Well here is what I suggest then. I assumed you want 12+ volts for motors or something. The pack is made up of over 20 cells so, yes, it can be split into a 7.4 Volt pack and will weight roughly half as much.
If you are running servos off this, I would suggest using 10C cells instead of 20C. You will still have 12,000 mAh but the current draw will be limited to 120 amps, instead of 240. If you will be drawing less than 100 amps, you don’t need the 20C cells. They are more expensive than the older 10C ones.
I can build a 10,000 mAh 7.4 Volt 10C pack for around $140ish. I’d have to look into if I have enough 10C cells for one or if I’d have to order some more in. The pack would handle 100 amps constant and around 160 amps burst. It would only be a few ounces heavier.
I could build them into 2 X 5000mAh packs and build a Y Harness for you to parallel them together when you use them. Then you can charge them separately. You are looking at a 2 hour charge at 1C to charge both packs (1 hour each) .
If you can tell me what will be running off them, I have my own test data for current draw from motors, servos and other electronics. I can figure out what you would need for the amount of time you want a pack to last.
Do you have a lipo balancer? I can install balance taps on the packs for balancing while charging if you do.
I use 2 cell lipo (7.4V) configurations for all my servos. I particularly like the Medusa brand BEC’s. They are very efficient and will accept up to 50V on some models. And have selectable voltage rates. They are around $20 to $25 and worth every penny. They work great when powering servos off a motor battery pack.
medusaproducts.com/BECs/BEC%20Main.htm
Check out their other products. They have some great stuff. I use their Power Analyser Pro as well. Awesome little thing.
For straight up Voltage regulating, I like the AnyVolt Converter for testing stuff. For robots it’s overkill but for the workbench, it’s great. They can be had for under $40 if you shop around. I know a source that has them for $50 CD if someone is interested. dimensionengineering.com/AnyVolt.htm
So it looks like I won’t be finding any unwanted SES parts. LOL I should hit Jim up for some used brackets. At least he couldn’t say he doesn’t have some (or hundreds) lying around. Could you image how much fun it would be to work for lynxmotion. Employee discounts…
By the way Tillin9, just wanted to mention. No pressure or anything about buying a pack off me. This isn’t a sales pitch, just trying to help out. I’m still learning alot about robots and for the most part, it’s a hobby for me right now. I’ll be asking loads of questions over time so I just want to help out where I can.
When you’re ready for a pack, feel free to ask me about it and shop around. Information is, and should always be, free.
Wow, thanks for taking all the time to educate me about this. Try to remember I know very little about LiPos, and come from a computer and light EE background, not an RC one., so I do have a few questions. My first question is what exactly is a BEC module? From the links it looks like some kind of DC-DC converter, but I’m a bit confused as to why one would want it?
My plan is to have the pack voltage be suitable for my servos and run them unregulated, then have suitable regulators on my electronics (LM2940 high efficiency 5V regulators). For the ITX board a DC-DC converter (picoPSU 6-24) which takes anywhere from 6-24 volts input and outputs the varied voltages the board runs at. The AnyVolt basically looks like a LM2940 (I think they copied the voltage current curves in the spec sheet) with a major heatsink and a PIC driving some 7 segments. I generally would only pull 500 mA with a single 2940 using a small sink, and I can’t really imagine using more than one for the electronics I plan on having.
Also, you can finally answer the question of what a pack balancer does and if/ why I need it. I had mentioned this on an earlier thread but I think you know a bunch more about LiPos than anybody else here.
That said, seeing your most recent posts, I think you initially way overspeced what I wanted.
My goal is to run a 12 servo biped, mini ITX Linux computer, and some minor electronics off the pack for a run-time of around 1 hour. Think either my current 5955 Scout or the possible Mega Scout. I think 8 amps is reasonable for both under mild stress (i.e. lugging equipment). The computer will at worst be a 34 watt Pentium III 733, meaning around 5 amps at 7.4V. I’m hoping I can get a mini-ITX Core Duo or Core Duo 2 (specifically a low voltage variant) so I can push that down a bunch. I’m aiming to be drawing around 1-2C most of the time. Unlike most RC applications, I don’t need anywhere near the amperage, so 10C packs are fine. The only reason I was interested in going LiPo is because of the weight issue. The mini-ITX board + equipment + the packs are only going to be around 2-3 lbs, but very heavy to either biped.
If you can do 10,000 mAh for around $150 at 1 lb or better, I’ll definitely buy. Breaking them down to two 5,000 mAh would be best since I was considering mounting them on the legs of the biped instead of the torso to help with weight. Granted, this might be an unmitigated disaster when trying to make it walk without stronger servos, but two packs do give some more mounting options. Plus I can always buy another 5014 and just charge the two packs separately if charging time really becomes an issue.
well, i may be able to help you out with a FEW brackets
however, if i did, they are black anodized, so i dont know how happy youd be about that, but i may be able to supply 3-4 C brackets and 3-4 multi purpose brackets, i atleast want to be able to build a BRAT jr if i ever get bored i soo, taking away the needed brackets for the BRAT jr…so i might be able to give you 4 C brackets and…3 multi purpose
Well a BEC is a “Battery Eliminator Circuit”. It’s need stems from R/C application. An R/C receiver needs 4.8 Volts to function and power the servos. On electric Models, a 7.2 to 35V power source may be used. You can use a 4.8V battery for the Rx and a 28 V battery for the motor but in Airplanes and Helicopters, saving every last ounce of weight can increase performance. So you use a BEC in-line with your high voltage power source for the motor, to provide an auxiliary power source of 4.8 Volts (Or 5 or 6 Volts) for your receiver and servos. This way you only use 1 battery pack for everything. It’s like a Voltage regulator basically.
We will use a simple 11.1 Volt, 2100mAh lipo pack for an example. Now this pack is made up of 3 cells (3.7 V per cell) in series. Each cell is 2100 mAh. This is called a 3S1P (3 cells in series, 1 set in parallel) Now lets say I made the same pack but used 6 X 1050 mAh cells. I would have 2 packs that are 3 in series to make 11.1V but wire those two packs of three in parallel to make the two 1050 packs, one 2100 pack. This is called 3S2P (3 cells in series, 2 sets in parallel) You can use any configuration of cells to build a custom pack. However the cells MUST be identical in discharge and capacity. And preferable new and never used.
So now you need a 6000 mAh pack at 14.8 Volts (which is 4 cells). I have a pile of 1500mAh loose cells. So I need to configure them equally to make your pack. So I know I need 4 cells in series to get 14.8 Volts. Done. Now I need to make 4 of those 4 cell packs. Ok. Now I solder the 4 X 4 cell packs in parallel to increase the mAh to 6000 (1500X4=6000).
So now we have a 4S4P 6000mAh 14.8V pack. (4 cells in series, 4 of them in parallel). So your pack that looks like one big pack once covered in shrink is actually 16 smaller cells creatively wired to give the desired ratings.
Now some of the most important rules with lipos is that you NEVER discharge them below 3.0V per cell, or they can swell and ignite. And you never over charge them by charging faster than 1 or 2 C or by charging them with more mAh than they can take. Or they could swell and ignite.
So when you hook your charger to this pack of 16 cells, how do you know that cell #13 is getting exactly the amount of mAh charge it requires? Or when you discharge them in your plane, how do you know if all the cells are discharged to 200 mAh and sitting at 3.1 Volts like your meter tells you? Maybe cell #4 is at 150mAh and 3.05 Volts because it’s chemistry is slightly different. And cell #11 is at 310mAh and 3.18 Volts for the same reason.
Now when your charger analyzes the battery and pumps 5800 mAh into your pack, because the packs overall capacity is at 200mAh, what happens to cell #11 that thinks the pack only needs 5690mAh? It takes the extra charge and sits overcharged. In reality, not a big deal. Lipo cells DO attempt to spread extra capacity among it’s fellow cells so everything is balanced. However, their ability to do this is limited.
Now what happens if cell #11 does the same thing after you discharge your pack again. Only now it might be holding 330 mAh instead of 310. So the charging process begins again. Now you have a problem. Over time, if cell #11 continues to be more efficient than the other cells, it will get to a point where it is being so over charged, that after many cycles of attempting to correct itself, it will just take too much charge and swell, or possibly rupture which would ignite the surrounding cells causing them to rupture.
The same can happen to cell #4 that was sitting at 150mAh instead of the pack average of 200mAH. Only cell # 4 will continue to discharge deeper than the others. And eventually, after many cycles, it may discharge below 3V, then below 2.9 volts, until it discharges low enough to become unstable and ignite.
I doubt that I need to explain what a lipo balancer is for anymore.
They are more important for larger pack containing many cells. A typical 3 cell or even 6 cell pack will probably be fine. And almost always is. But I have lipo packs that put out 50V at 300 Amps. That kind of power can weld booster cables together. And these packs contain many large groups totaling over 80 cells. This is when I want to be sure every single cell is healthy and keeping up to the pack. Not because the pack is worth $600 but because if it were to ever ignite, there would be no stopping it until it burned itself out. And it’s sitting in my workshop next to me right now. In my house. So, ya, I own a few $30 and $60 lipo balancers. LOL
Higher end pack come with something called balancing taps. They are a multiwire plug that hangs out of the shrink and basically provides a common ground and a live positive to each cell in that pack. **When charging, you can plug this balancing tap into a lipo balancer (basically just a little circuit board with some lights) While you are charging the battery from the main leads, the lipo balancer will help distribute the power to provide more to low cells and less to high cells. Just as the name implies, it balances the cells so they all end up identical in voltage and capacity. **
Not a necessary item if you packs are made from high quality, brand new cells. But when one can be had for $20 or $30, it’s hard to justify not buying one for a $300 pack that sits in your $200,000 flammable house.
I can even do 4 packs with wiring harnesses to give you more diversity. Plus I can configure 2 packs into long, thin bars or shorter, thicker cubes.
Really the possibilities are endless. I’ll see what I can do for a price if you want one and then maybe send me some pictures of where you would want them mounted with something in the pictures to give me some size reference. Then I can load the pictures into a photo program and import a few pack sizes to scale with your photo to see where they would fit best according to your suggestions.
It might be an option to send me specifics of where you want them mounted or send me an idea of what you want your feet look like and what will mounted on them and I can fabricate some carbon fiber feet with lipo cell built into them, sandwiched between the carbon. With carbon feet and lipos they would probably weights just slightly more than your aluminum ones. Plus they would be power pack feet.
I hope this answers some of your questions. Some of the stuff is over simplified but I don’t want to write a book.
I don’t want you to give up some brackets if you really don’t want to. I’m a very reasonable guy and if you need a lipo pack, I’m sure we could work something out. You and the others I have spoke with are regulars on the board and seem like stand up guys. I wouldn’t have a problem working something out with someone well known on the forums, since it would be easy to find them.
no, i dont mind it man, i dont really use them much anymore as i am trying to make a secret project of mine happen , so i would be able to give you these SES brackets as this project doesn’t require any of them
i would be interested in a battery pack though, because i need 12 volts for the batteries and some pretty high mAh from the batteies, because i will be running a lot of stuff off of it, and if not 1 battery pack, probably 2 decent ones
Chunga, what are you running off it? servos? motors? Roughly what type of discharge are you looking at?In amps.
I could certainly use the brackets even if they are black.
Are you looking for a lipo pack or a NimH pack? Lipo I can make in 3.7V variables. So 3.7, 7.4, 11.1, 14.8, 22.2, etc. NiMh I can make in 1.2V increatements.
The 4000 mAh sub-C cells I have now are awesome. They are conditioned and matched as well.
Oh, and black, blue tint or clear shrink? I like the clear and blue because you can see the cells. Here’s 2 of my 14 cell packs I run in series as a 28 cell pack in clear with the 4000 mAh cells for my E-Raptor Heli. These weren’t built in my jig so they aren’t real pretty. I whipped them up for some test flights one afternoon and never rebuilt them.
And a 6000 mAh 11.1V lipo made from 3 2000 mAh factory packs. I normally disassemble the cells completely and maek a new pack but I was in a hurry so I hard wired them under the shrink.
stalled they draw 4 amps, but i highly doubt they will stall because i will be running 2 per track and the vehicle will not be that big so id say in total have 1 1/2 - 2 amps at any given time because the arm servos will be relaxed/off when the motors are running and vise versa, maybe some sensors too and the electronics, but those draw close to nothing
so im thinking sub c cells in 2 serparate packes of 5 for 12 volts maybe the the 4000 mAh ones i see in the picture. that way i can charge them serparatly
btw, when you see this PM me so we dont make the post huge with our convo
Okay…I think I have the BED, which is really only for RC applications where weight is an even bigger issue than robotics (to eliminate extra batteries for electronics and low power devices) and some hobbyists aren’t comfortable making their own regulator circuits, which is understandable since even secondary systems can pull a good amount of amps on a model. Fortunately, using switching voltage regulators is something I’m fairly good at. 8) In part of one of my EE courses we took an indepth look at various designs including the Black regulator which actually gets around 90+% efficiency for a 6-12 to 5V conversion. I can provide links if you want to explore that kind of electronic engineering, but for most of my needs a simple 3-terminal and some capacitors will do, they’re smaller, simpler, lighter and get ~80% efficiency.
The balancer sounds like a really good thing consdiering the size of the pack I’m looking at, the relative costs, and now that I know how LiPos can get further unbalanced after many charging and discharging cycles. I somehow through that this would correct itself automatically due to internal resistance, but I guess it doesn’t. I do have some follow-ups here, mainly does my charger have to support the balancer, or is this something that is part of the pack? From what I can find online, it seems the balancer will just allow the individual cell to discharge during a charge cycle, so that the charger charging the whole pack won’t hit a peak voltage delta until the other cells which are undercharged reach capacity also. This doesn’t necessary imply any support by the charger, though some places say some research needs to be done to see if the charger supports the balancer. Since having the extra circuit, which is only triggered at around 4.20V is dead weight during use, maybe some chargers have this built-in or have it as a module between the pack and the charger?
As far as the actual design, I’m impressed by your enthusiasm but without proper testing, planning for a specific design like power pack feet could be foolish. Considering each foot pad itself weighs a few grams at worst, I sincerely doubt you could make carbon fiber feet with packs that weighed in the same ballpark. Yes, the carbon fiber part could weigh much less than my current stock Lynx SES reverse knee biped feet (ARF-02), but you have to be careful where you add the packs. 1oz of weight at a sufficient distance from a critical joint can act like a lever and appear to be much more massive. Think of it like this: on a robot arm, you won’t ever want to put a pack on the end of the arm, when you could put it in the base. With a biped, this gets a lot more complicated. Weight on torso means more torque used to stand, and more for certain balancing parts of the gait where the center of mass is far from the supporting foot. More weight on the feet means less torque to stand, but more to lift a foot. It is unclear exactly how this effects balancing. I.e. would the extra weight on the planted foot completely offset the effects of having more eight on the raised foot? How would it effect the distance my center of mass can be from the balance point? I have the test setup to find the answer (i.e. a high current ammeter, logging scope, and some adjustable weights I can strap to my bot), just not the time to do it till later next week. One of my goals was to find out the dynamics of some useful gaits and then come up with mathematical models of them so some intelligence can be used in future designs. Considering the bot is just a bunch of levers and servo currents are directly proportional to torques, some kind of vector analysis should be possible (disclaimer I am a physicist in real life who works on computer models).
The design that would be best would probably be two 4-4.5" by 1.75-2" by ~0.5" rectangular prisms. These could mount easily on the top of my current Scout by the SCC-32 or on the legs (specifically the Lynx dual multipurpose, ASB-15). These would be small enough to mount more or less anywhere on the Mega Scout.
I didn’t realize your feet were so light. Or that the weight int he foot could change the dynamics of the gait. In all fairness, I’m pretty new to robotics. Haven’t done much other than goal specific prototypes. Not much that walks.
And the balancer plugs into the taps coming out of the pack. And the charger plugs into the main power plug coming out of the pack. No matter what charger you use, you can plug a balancer into your pack, so long as it has the taps for it. It works independently of the charger. There are some high end chargers that have balancers built in that you can plug your taps into. But 98% don’t have this.
So you would basically want the packs to fit into a lynx ASB-15 Dual bracket?
I’ll have to order one directly from Jim since I don’t think robotshop carries that bracket. There are few things from the SES they don’t carry, like the aluminum servo horns.
If you could get me the exact dimensions of the bracket, I’ll see what I can do. I don’t mind building the pack, even if you don’t buy it. I can always get rid of it down the road.
Hey, no problem we’re all learning here. Sorry if I sounded a bit harsh. I think I’ve more than demonstrated my lack of knowledge about batteries. On that note, thanks again for educating me. While I don’t think I could build a pack myself just yet, I think I could use one safely, and yea I think tabs is definitely the way to go.
As for the design, I was very unclear. I don’t want it to fit in the bracket, since the servos go in there. If you look closely at a Scout you’ll see this is basically the largest flat surface on the leg, it’s essentially the shin. Another possible spot is the meeting point of the two C brackets on the hip. Both flat spaces are roughly the same size. The battery packs would be kind of stuck on, using zip ties at worst, probably some sort of aluminum mount I make in our machine shop here. A hi-res of a scout is here, lynxmotion.com/images/hi-res/bps01.jpg, it might help you visualize this, might not . I was thinking I might be able to strap a pack to the backside of the leg (again as I initially said, this may not be a good idea at all). I currently have a standard Lynx 7.2V 6 AAA cell pack (1600 mAh) that fits there with room to spare and doesn’t seem to cause that much trouble when walking (though I only have one so there is a limp in my tests). I mention this so you can see approximately what size would be ideal. I don’t think a LiPo pack could be made with 5000 mAh capacity to fit in such a space, but I could be wrong. I could probably get two 3200 mAh sub-C NiMH packs, one on each leg on the bot without much fuss, which is a more realistic size for the power capacity I want. I don’t think you need to buy a bracket for this purpose, though if you’re building a Scout you’ll get one anyway.
My main idea is to be able to try this on the shin, hip, and torso. If any of those positions work, great. However, if all give problems, its not a total wash, since the packs are capable of powering the Mega Scout and they should fit fine there anyway. I may just have to settle for something much smaller on the standard Scout and use a high-end microcontroller instead of a PC for the brain. Also, I should mention I have a Lynx 209 biped chasis, so I have two different types of torsos and can reconfigure the legs (the 209 and Scout legs are different). I had thought about opening up a 209 chasis (replacing the hex standoffs with longer rods) so I might be able to pack in more equipment that way. Again, these are the tests I will be doing all next week in addition to getting some web space to chronical all my robotic adventures.
I see now. i thought you were going to mount an additional dual mount bracket on the legs to hold the lipos.
5000Mah pack can be fit onto there. You can actually buy 5000mAh and 10,000 mAh cells. Just one cell has that capacity so you don’t need to piggyback multiple cells. However they are also a little more pricey. I could definitely do 2 X 4000 mAh packs in that space. I’ll see if I can find some cells that are lower C rating. If I can find older cells that are 10C or 8C, most people clearance them because 15 and 20C are the norm and 30C are the new thing. Even with older 8C cells you will have around 60 amp continuous, which I don’t think the servos and controller will even come close to drawing.
Tillin9, I whipped up 2 X 3.7V 6000mAh packs. I wired the 2000mAh cells in parallel so I could use 3 cells per pack and I can make a harness to plug them in, in series, for a 6000mAh 7.4V pack.
Each pack weights 3.91 oz. and is 3 7/8" long X 1 3/8" wide X 3/4" thick.
That should be within your previous measurements.
I had some 2000mAh cells kicking around so I just built this up so you would have an idea of size and weight. If you want to go bigger, we can go bigger. If you want to go smaller, I have a 1000mAh cells I can make into a 3000mAh 7.4 Volt pack. These are some real tiny cells, they are only 1/8" thick and light as a feather. Each pack would weight roughly 3 oz.
Here is the 6000mAh pair. I took some pictures of the pack laying on 2 Servo-mount brackets (I though it would be the closest thing to the double bracket I had for size reference). It looks as though it should fit nicely on the leg of your biped.
I think the immediate answer is its still to expensive for me to do this just yet. Sorry.
Sorry if I sounded a bit harsh. I think I’ve more than demonstrated my lack of knowledge about batteries. On that note, thanks again for educating me. While I don’t think I could build a pack myself just yet, I think I could use one safely, and yea I think tabs is definitely the way to go. 