Hey guys,
I found this site a few days ago and wondered if these packs are any good for the hexapod.
They say that they are 6.4-7.2 Volts. Can i just attach this pack to my ssc-32, for the VS (servo power)? or do i need another product?
And which is the cheapest option to recharge it again?
Here is the link:
robotmarketplace.com/products/battery_build_li-ion.html
I want the 3200mAh.
Anyone?? Can i use this to power my servo’s?
the link you posted goes to a generic battery builder screen. any selections you made are probably stored in cookies on your computer and anybody else just gets the default initial starting screen.
a 2S LiFePO4 pack is a little hot, that is too much voltage, for normal hobby servos and it would be advisable to use a BEC voltage regulator set to 6V. There are two BEC devices in common use by folks on this forum, the Turnigy and Castle Creations. Neither of these will handle the full current requiremets of a fully loaded hex with good servos on it. Thus you would probably need a pair of BEC, one on VS1 and one on VS2 with the VS2=VS1 jumpers removed.
Before you go and buy a 3200mAh pack you might want to do a test first. Find the weight of the pack and add that much weight to the bot. See if it can actually support the weight of the pack. It’d be a shame to get it, then find the servos can’t support the weight. Because you have built the bot with very weak servos you really need to watch the weight…
oh is this the HS-422 based hex build? heh.
422s pull so little current that you might actually get away with 1 BEC… and then I’d look at the total weight for a 4S pack of the 1200maH 18650 sized LiFePO4 cells and see if that is prohibitive. Because the BEC is roughly a constant power conversion (less it’s efficiency which is probably around 85-90%) it behooves you to push the input voltage as high as the BEC will allow. Because the servos you are using are analog and pretty low power I would recommed a 6V operating voltage. This way you will get roughly the equivalent of 2000 to 2400mahr or so at your operating point of 6V from the 4S 1200mahr string.
actually since 422s are analog… anybody remember if they will run off 7 to 8V or so without overheating? might beat the snot out of the servos when freshly charged but you might not need the BEC. 
it’s using Futaba but the specs on the servos are roughly the same as a 422.
Futaba S3003 57 oz. in.
Hitec HS-422 57 oz. in.
We used to run the 422’s straight off a 7.2vdc NiMH pack in our old EH2 hexapods. They seemed to handle it very well. I don’t remember ever having any servo problems with that kit.
as far as i know the s3003 have a max power of 7.2 volts so that means i can attach it derectly or i it still too much??
The reaon why i want this pack is because it only weights 0.36 LBS or about 160 grams
If you select the 3200mA pack there is only one cell possibillity. thats the one i meant.
How did you come to this knowledge?
The servo is rated for 4.8-6vdc. I do not know if it can handle 7.2 directly or not. I have no experience with it.
Probably let the magic smoke out!
Alan KM6VV
It showed up when I clicked the link:
http://www.robotmarketplace.com/products/images/bp_configs/cell57.jpg
I say BEC it…
Yeah that is an interesting idea!
I have very limited space on my 'quad, mainly because I just designed in a small 6V 1600 mAh LM battery pack.
It might be possible to design a pack specifically to fit my available space with this battery. And I agree that the BEC would be a good idea to get the voltage regulated down as needed.
So what power connectors, charging taps do you recommend?
Alan KM6VV
So how many of these would i need for 22 servos?
Alan,
hmm, well the LM 1600mah nimh pack is using 5xAA cells so that is roughly 50mm high x 95mm long by 20mm thick.
the 1200 mah LiFePO4 cells on that page are 1200mah in an 18mm x 65mm cell but are also 3.2V nom vs. the 1.2v nom of a NiMH.
So the question is if you can make a LiFePO4 pack with more capacity, provided you are willing to sign off on the additional cost of a BEC, to fit in the same space. You could figure it out in Watt-Hours… 6V x 1.6AH = 9.6WHr, but factor in nom 85% eff. of the BEC and it’s more like 11.3WH. So 11.3 / 1.2A = 9.4V minimum. It really seems like the 50mm dimension is going to force you to orient the 18x65mm cells the other way thus limiting you to only a 3S pack… 3.2V x 3 = 9.6V… just barely worth it. If you can increase your available area to support a 4S configuration it is certainly worth the effort as you get another 30% or so capacity. It is obviously more expensive though… and should also consider the 4S pack will need a LiFePO4 aware charger with balancing.
Mike this is only a 1.5A BEC… would want one of these per servo I think. 
22 servos is a lot, even if they are your S3003s. I think your best (conservative) bet would be two ~10A rated BEC set to 6V output and a 4S pack of the 3200mahr cells. From an energy standpoint his would be roughly equivalent to a 7000mahr 6V pack, and weigh roughly 350g in cells plus another 25-30g for the two BECs. It’s pretty heavy. Dropping to 3S you would shed about 85g and still be roughly 5500mahr of capacity.
Put a 10oz weight on your hex at roughly the location the battery cells would go and see if it can still get up and move around.
Eddie,
The 1" diameter is what I don’t like the most.
I currently have planned for a 2" x 2.8" battery, or maybe 4.375" x 1.875" (possible). I have a lot of looking to do. 4S is OK, and $15 or whatever for a BEC is also OK. Charger extra!
I’m still weighing through all of the different batteries!
Thanks!
Alan KM6VV
I’m sorry I was suggesting the 1200mah cells in your application not the 3200mahr cells mano is discussing. The 1200mahr cells are a standard 4/3A or 18650 package which is 18mm dia x 65.0mm long.
2" x 2.8" is roughly 51mm x 71mm. 18mm x 3 = 54mm so allowing for some heat shrink figure on 55mm x 68mm for a 3S flat pack of 18650 cells. It is too bad regular Li-ion cells only discharge at about 2 to 3C vs. the 10C of LiFePO4. The energy density of LiFePO4 isn’t a whole lot higher than NiMH and it’s a lot less than Li-ion. Of course there’s the whole safety thing to consider as well. Heh. 
I don’t see where the 4.375" x 1.875" area works well for either the 18650 or 26650 size cells. Depending on the height available maybe you could come up with a 4S of 18650 in a staggered brick configuration.
Doesn’t sound like 3 cells would be worth it. And my current layout is bound by the size of chassis I can comfortably make with my mill. Maybe I can put the batteries on an upper deck. the 1" diameter of the batteries is hard to work around with my present design.
I’m not even seeing a 1200 mAh battery on that page. Some of the rectangular battery packs elsewhere looked interesting.
Do three battery packs also need the equalizing charger?
Alan KM6VV
Ideally yes. Because of the way LiFePO4 cells charge, or more specifically the way their terminal voltage changes as they approach full charge, long term you will not get very good life out of your pack without balancing them. The balancer doesn’t necessarily need to be integral to the charger. Something like a Hyperion LBA10 is around $35USD and goes between the charger and the pack while charging and/or can balance in disconnected mode without the charger attached. A nice thing about using something like the LBA10 is if you have a benchtop power supply and it can run in CV or CC mode then you don’t even need a charger per se… set the CC limit to the 1C pack rate, set the CV to 4.2V/cell, and the LBA10 will balance and disconnect the pack from the supply when the pack is fully charged. 
so since i started this topic and still have no answer;
Is this pack (in post one) usable and how many of those converters do i need?
