A123 2S2P - change to 23T pinion gear?
 

Hi,

I am using A123 2S2P batteries in my Flux HP. They are a little bit less power than 2S LiPo (6,6 versus 7,4). So if I change to 23T pinion gear will I get +/- the same speed as with 2S LiPo and will it not stress my system to much? I have changed tires and wheels to

http://www.hpieurope.com/piw.php?lang=en&partNo=4925

Other than that everything is stock...

Thank you.

Audrius

On stock tyres and 20t pinion the system pulls 110 Amps on a burst from 2s2p A123 as opposed to 120 Amps from Lipo, so given 2S2P is 4600mah 30/60C for 138 Amps constant, 22/23t pinion "should" be ok. And if you're running Nubz I'd recommend it, I ran 4s lipo on 20t pinion with those tyres and the motor felt VERY undergeared.

4s A123 is no where near enough power for a truck the size and weight of the flux, you want to be running 5s2p or more like 6s2p- 4s2p is barely any better than 3s lipo, and thats just laughable in a 10lb truck...

Well, I think for Off-road race truck weight is important. And two packs of 2s2p are lighter and has controllable speed. I have to check how two sets of 3s2p will behave, but at the moment for my local track two 2s2p packs are ok. That is how our local track looks

http://www.rc-cars.lt/index.php?opti...=129&Itemid=85

And I think with standard battery trays max A123 setup would be 2x 3s2p or 2s3p... am I wrong...?

Thats a pretty tight track for something as big as a flux, no wonder you dont need much speed- gearing down would be a very good idea to spare the batts some strain (lower the voltage, lower you gear if keeping the same kv motor).

Not sure on the battery compartment measurements, but I would have though you could fit 5 A123 cells in each side, if they were arranged side by side (in a row within the compartment). I know A123s are pretty cheap, but lipos are also very cheap these days, and alot lighter than the A123s, might work out better for you.

Anyway, I wouldnt try to gear the 4s2p A123 setup the same as the 4s lipo setup, you will definately need to go down in gearing to prevent over drawing the A123s which will have a knock-on effect with the esc (ripple current and all that fun stuff that the MMM doesnt like).

Hi,

so if I go with 18T pinion gear it would be more or less ok?
Yes, I am looking at hard case LiPo, just need to figure out which I need. At the moment in tournament we do three 5min qualification runs and one 20min final run. So I have to calculate what sizes do I need for that... Could you suggest some numbers, please? mAh, and C...

Depends what pinion you are using currently, but try 18 and see how it feels.

I would say you are wanting the biggest mah you can fit really, so 5000mah ideally, and 25-30c would be fine (not a terribly demanding setup, most people want more speed and power so they need more battery...). If you look at the hobbycity.com website, they have some nice hardcased 5000mah 30c lipos, or there is always the SMC or even venom (yuk) lipos with a hardace, not to mention all the items Mike sells in the rc-monster store. Depends on your budget really, but done let me sway you too much, I just know that a 20 minute final race is gonna need fairly big mah batts to last the full time without stopping for a battery change. I dont suppose you could measure the insides of the battery trays, that might give a better idea as to what will fit and what wont.

Battery trays dimensions when looking from side of the truck:

H=45mm
W=196mm
D=30mm

If battery would be W<180mm and D<27mm then H could be ~51mm

I disagree, I run 2* 2s2p A123 in my Flux now and have tried the hardcase lipo path (Harris rc 30C and then Intellect 40C), and I can say that the A123 while it robs a bit of top end power is kinder on the ESC, and is in NO way underpowered on stock gearing.

Desktop theories are one thing, but real world testing is another.

On further consideration, perhaps 5s is the go, would I benefit reconfiguring my 2 * 2s2p packs into a pair of 5s1p (with a couple of extras) and then running the packs in parallel? I'd have to assemble them side by side, remove the battery box lids and secure with Velcro straps inside the battery box bottom.

For bashing, that would be a much better setup; you have to remember that castle states a 2p setup MUST be used with the MMM/ Flux, otherwise its a warrenty void issue (voltage drops under load too much causing ripple currents and whatnot that the esc doesnt like).

Speed wise, if 4s a123 is fine, then I would use 4s2p for better runtime and increased punch, but 5s2p is nice as its equals 4s lipo, which is perfect for a 2200kv motor.

All personal preference at the end of the day though.. :smile: