brushless and A123 questions
 

Hey all,
I tried out my E-maxx today with new Batteries, I was really hoping for a big boost from my previous packs. (6c 3300's) for 14.4 Volts

I was disappointed in the performance gain. Seemed kinda minimal improvement. My setup is as follows

wanderer 9XL
BK 12020 controller
Big Joe Tires
Forget the exact tooth on the pinion, I think it is 15.
A123 6s1p. (20 Volts)
Everything else is stock.


Now for the questions.
1) Do I need to go to a 6s2p pack??
2) What chassis would fit these packs and work good for bashing? (Packs are 3s side by side. I put one pack on each side of the stock chassis even though it did not fit...... (Had to rig it temporarly to test)
3) I am thinking about smaller tires.. Maybe the proline mulchers 40 series and some of the axial bead less rims. Would tha be a good set up?
4) What else is really needed for Bashing... Steering upgrade?

Highflier

You really do need to go to a 2P configuration with the A123 cells. In 1P configuration, they drop a lot of voltage under load and then can't deliver the current. In 2P configuration, you'll see a bigger difference.

As for bullet proofing the E-Maxx, it's gonna take a lot of upgrading. I won't say that the E-Maxx is a "weak" truck, but I will say that it has troubles withstanding the rigors of a brushless system, especially if you run that 9XL on 6S A123.

The Axial bead lock rims look nice, but they didn't hold up very long for us. The tires kept popping out.

Heres my suggestions:

FLM chassis
Proline or UE servo saver
Proline Crime Fighter MT tires
Proline standard dish rims. (I would go with 23mm)

6s2p seems like alot of weight. what would give me better accelearation.
6s1p
or
5s2p

Oh and how well can you fit 4 3s packs into the FLM extendedd chassis? I have 3s packs since that is what I use in RC combat airplanes. Which by the way is a blast.

Off to go check out prices on the Chassis and servo saver...

Thanks for the advice!
Highflier

Well I just scored another 10 cells of A123, So now I have to figure out how to configure them.

Still need answer on if I should go for 5s2p on this drive train

9xl wanderer
BK warrior 12020 controller

Highflier

5S2P will give you more punch, but it's kind of an unfair comparison.

In any case, if 10 cells is your limit, then 5S2P is the way to go. If you are considering going with the A123 cells, you really need to decide if they are indeed what you need, or whether they will acutally give you any benefit.

As you noted, they are very heavy. A 5S 5Ah lipo pack will cost you about the same as a 5S2P 4.6Ah A123 pack, but the lipo pack will give you better runtime and a higher voltage.

The lipo pack also weighs juat a bit over a pound and the 5S2P A123 pack will weigh closer to two pounds.

The A123s offer a quicker charge time, but only if you have a charger capable of allowing you to avail yourself of that benefit. I run mostly 5S2P 8Ah packs and get around 45 minutes of runtime with those and they charge in an hour. With the A123 pack, I'd get around 25 minutes, but they charge in around half an hour. Until I can get a charger that can charge at a 20A rate, I'm going to stick to lipo.

i just noticed last night looking at my flm ext. chassis, there is alot of room behind the trans with the stock speed controller gone.

My charger can charge A123 at 8 Amps, Also you can create a Charger that will charge them in under 10 minutes for very cheap... There is a thread about it on Ezone. It's not much more then 18 feet of wire connected to a 12 volt car battery.

However charge time is not my biggest concern. I would go Lipo but it's the cost. a 4s 5Ah pack is ~$200.00, and a 5s is $250.00 I was able to snag 10 cells of A123 for just under $100.00

I'll give 5s2p a try and see if I am happy with Power. I would like to have enough so that if I punch the throttle while I am already going 10mph that there is enough to spin the wheels.

Since I am just bashing it I don't think weight will be a huge issue. After all 10 A123 cells probably are not much different then the stock NMHI packs


Thanks for the info.


Highflier
PS. I will be happy if I get 20-30 minutes of bashing time per pack. I'll have enough cells if I do this right to have
4 3s airplane packs
or
2 5s2p E-maxx packs

you'll be happy with 5s a123 packs...and like you said, you can share the packs with your plane. another note about them is that they have a charge life of over 1,000 cycles - lipo is only a bit over 200. that was the selling point for me - plus they're stupid safe (which i need). you can abuse these cells all you like (within reason) and they hold the same voltage and runtime.

Like Clod pointed out, the adv of the A123s cells are safety, durability, lifespan and cost. I run A123s, but I may get 1 ltwht lipo pack for racing. Also note, that the A123s do not lose performance over theirlife span, only capacity. The IR actually goes down w/ age, so they get better, but lose capacity only. NIMH IR goes up ovr the life, so they lose power and cap. In short A123s are heavy but badass cells.


FWIW tho, they are limited to 70A discharge (30C) before they drop alot of voltage. You are prolly pulling 100A+. You need 2P.

5S2P is nearly equiv to a good 4S lipo pack. Mine weighs 780g. My TrueRC 4S 8K pack weighs ~700g, so... Runtimes were 25min vs 1hr bashing around.

you lose a bit of top spd w/ 5s over the 6S, but much better runtime and not abusing the cells. For a basher the weight is not that big of deal, and still weighs less than a 12cell NIMH pack.

OTOH, you could just run upto 8s A123 on the BK. You could do that, get a cooler motor, like a 11XL or so, adn end up in a better place.

The motor would be more eff, so more power to the ground and less heat, amp draw would be OK for a 1P config, so you could lose some weight over a 10cell pack. A 8S1P pack should weigh less than 650g. I'm now running a 10S A123 pack w/ a 1100 kv motor and everything runs dead stone cold. :) Once you go HV you don't go back.

thanks for all the help so far
 

I don't think so the BK controller is rated to 20NMHI cells right? I thought 6s A123 cells would be the limit
I have thought about 4s2p and getting a 7xl or 8xl motor instead of the 9xl

Eventually I may get another power train and give this one to my wife. Strange as it sounds we go for walks in the park 1-2 miles and bash out E-maxxes on the way. We just carry a spare pack and turn around before the first pack is dead. Funny thing is she has a 100% stock maxx and mine is stock except the motor/controller. I have been running 14.4 volts on the system till now. My system still has more power and the run time is at least 25% longer :)

The 5s2p may be perfect for me, since run time is more importent then top end... However punch is so much fun :diablo:

Highflier

PS. I am down to 2 different chassis.
FLM ext or a super sized one from RC-Cellar that is extended by 5". Anybody try that one out for bashing.. As a basher which would be more fun..

That's if you are figuring the voltage limit @ 1.2V/cell, but NIMH charge to ~1.45V/cell off the charger, which would be ~29V for 20cells. 8S A123 would charge to ~29V. BK is a little dumb tho, that's why few use their controllers anymore, so you'd have to confirm everything. I know for a fact 6S lipo was common on the controllers, tho not sure if anyone ever ran 7S (maybe due the the odd # of cells tho.)

Anyway, running higher V does not mean more top end if you match it to the proper motor w/ lower turns. You are just making power w/ V instead of so many Amps. The end result is less wasted power and less heat. A 8s1p setup would run cooler and longer than a 4s2p setup with a similarly matched motor. You don't need to experiment if you don't want to, just letting you know the option is there.

6s is the limit I would go.. simple because I know a guy who tried 6s lipo and had 2 controllers fail. First then the replacment. He was told that he had overvolts and that they would not support him anymore. 6S A123 is obviously below the spec and closer to 5s lipos.

I went with the 9xl so that I could run higher voltage. 5s or 6s seems to make sense to me right now. It has to run cooler then a 7xl at the lower voltage.
I am thinking that the 5s2p maybe the sweet spot for me. I just need to find a way to test it without having a big hassle with Batteries.

For charging I plan on using zip chargers (8-10 min for a 3s pack. I'll run 2 at the same time and then I will take the 2s packs and put them in series and charge as a sinlge 4s pack at 8 amps on my hyperion charger.

So If I get 2 complete setups I can charge one while I run the other. The charge should take about 15-20 min. I most likely will only have battery swap as my down time :)

All this for a fair cost
$200 for dewalt cells (20 cells)
$200 for hypersion charger/balancer
$20.00 for 2 zip chargers

so for a total of $420.00 I can run 1 E-maxx nonstop for 1000 plus runs.

As a added benifit when I fly my combat planes I will have 4 3s packs and will be able to fly non stop also :) here is a funny one for you. The combat planes are cheaper then the trucks:yes: They break far less I can crash them in midair or into the ground and most of the time the repairs if any are below 5.00. The cost of the planes is cheaper also. If there is anybody in the philly area that wants to check them out let me know, I could use a local truck guy to help me along on the E-maxx.

Highflier

hooooo boy, good thing i don't live closer - combat planes would be fun... i'd be too tempted to get my own. or a jet. always thought jets were cool too, but mucho more expensive.