Which Controller for My Application?
 

So I wanna run a 22.2v system w/ a Lehner 3100XL (maybe the 2800XL) in my non-bling maxx (meaning, its lighter than stock :D ). My requirements are to go fast (just under 50 mph) on a big track for a long time (up to :30 minutes). Probably not an uncommon desire/request.

I'm definately going LiPo. I think the TP8000-3S4P (*2) is the ticket (22.2v, 8000mah).

I'm looking at the BK controllers. The 9918 for its price ($200 less then the next step up which is $400) *might* work for me. But w/ ambient temps in So. Cal @ 100F-110F I need a controller that's not going to faint, but I of course don't wanna pay for total and complete overkill either.


18120 - 22.2v seems like this controller will be at its voltage limit, what effect will running a long race have on it?

30120 - limited to 42000rpm? yuk

18150 - see voltage issue w/ 18120

30150 - limited to 42000rpm also.

I think I'd feel more comfortable w/ something like a "20120" that doesn't have a 42000rpm rev limit.


Not sure which controller I should get. Any suggestions?

tia

You might find the answer here;

All the BK/Lehner controllers that suit 18 cells can be used on 20 cells

and the 30 cell controllers can be used on 36 cells

The RPM limit is a matter of time. The 42000 rpm limit is weird, Some contradictions are rising questionmarks in my head at this moment about this;

It's about the hardware rev. rev1 = 12 mhz, rev2 = 24 mhz. The 12mhz= 42k limited. i guess it's a matter of the used transistors/fetts, that can't be used on this frequency, or the 24mhz gives a electronical noise in what way ever.

if you see this and this data/information sheets, you will see that the micro controller is able to kick out some more rpm's.. (Mike is asking BK, when this limit will be gone though)

You need some kind of alarm, that tells you when the lipoly voltage drops bellow the 3V/cell It will shorten the lifespan of your lipo badly if you don't keep a close eye on it.

As rene said, the 18 cell controllers are approved for 20 cells, so you won't have any trouble with that area. I have run 22.2 volts through my warrior with no problems. I wouldn't go with such a hot motor, though. I use an xl2400 and it is almost too fast for the track on 18.5 volts. For 22.2 volts, I would use an xl2000 motor (or maybe even an xl1600). The warrior will handle the voltage on either of these motors just fine - even in So-Cal. Trust me when I say the xl3100 is too much motor for that voltage.

They reached 50 mph on 12 cells with the XL3100.. (14.4 V vs 22.2.. )

I cant imagine 50 mph - in an emaxx - and forget about 50 on a track.

measured with GPS, by two or three different people. allmost complete stockmaxx, made it a bit lighter, with other wheels/dropped the shifting servo.

There is a thread about it on maxxtraxx, it goes by the name '49,7 mph on 12 cells' or something like that.

Also confirmed and tested by a user that is/was on this board, Promod. I can believe it, because 12 GP3300's can throw out 1200 watts. that's about 1,5 bhp, with 10 percent lost of the motor/controller.

I don't think these people are not serious.

Thanks one and all for the info. I have some follow up questions, if you will.

Agreed, too big an investment to lose. Any recommendation on an audible alarm or cutoff? I found this, small, light, and inexpensive -> http://www.customidea.com/hrpolyx.php

I'm not gonna mess w/ the rpm issue and the 30xxx series. I'll probably go w/ the 18120.

The track I race on is rather large. Wide, long, long straights, etc. I don't envision 50mph except for the main straight...and that's only when I'm properly hooked up (i.e. , straight). I would like the potential for 50mph because I'd like to push the limits.

When you say its too much motor do you mean the 3100 will not be capable of pushing an 8-9 pound truck or that it'll spin out of the can at those RPM's (:D )? (technically by about 3,000 rpm...if I ever hit the max).

If I go w/ a lower RPM/v motor I'll get more torque and less top end. I can tell you that twin Titan's w/ 14 (16.8v) matched gp3300's is more than sufficient torque for my truck...anymore and I'm riding wheelies and increasing wheel spin. So based on the weight loss of 1 Titan motor (10oz?) and 3oz off another (replaced w/ Lehner) I don't believe more torque is necessary.

btw, anybody have good numbers on the stock 550's? I'm curious about their ratings.


thx in advance for the comments! I'm just trying to make sure I get exactly (or at least very close) to what I want.

Another consideration for lipo discharge cut-off:
http://www2.towerhobbies.com/cgi-bin...3&I=LXJDJ0&P=K
FMA Direct Auto Cell Detect/Low Volt Cut-Off Device

A device designed for that, specifically.

Cool, I'll add that to my list.

If anybody has experience w/ these things I'd love to hear about 'em.

I don't know what your timing is like, but I plan to have 2 Kokam 3s 3200 packs with that low voltage cut-off device on or before next Thursday, 5/26. I'll install and report back after that.

Increased torque is not optional with high voltage brushless motors! It will happen no matter what. The xl3100 will run a bit hot at that voltage and will be too powerful to handle in my opinion. As I said, the xl2400 on 22.2 volts will achieve your speed desires with the proper gearing, but will run cooler. The xl2000 would be my choice. ASgain, this will provide plenty of speed/power, but will have better runtimes and cooler operation vs. the xl3100. I doubt you will see 50 mph on a racetrack anyways (40mph if your lucky).

Excellent.

I'm going to purchase my motor and speed control sometime this week. My LiPo decision will be made in a couple of weeks. I'm interested to see how well this thing works for you.

thx!

Granted. But I don't need excessive oz-in...which is why I've read about other's experiences (which are very subjective and relative to many person dependent variables) and graph motor performance w/ various voltage/current combinations. Oddly enough I'm thinking the Lehner's are a great choice (based on user experience) even though I can't put their specs into my calculator.

I don't wanna run my motor too hot as I'd like to run in the long mains, so I'll bump it down to the 2800.

I'll stick w/ the stock gearing for now and see how I like the performance & runtime.

The LiPo's and speed control are the expensive components, I don't mind getting a different motor to alter speed/torque/runtime/temps if I don't like the 2800. :)


thx!

Even the 2800 will be quite warm with that voltage. Most motors are at their highest efficiency(lowest heat generated through inefficiency) in the 30-40k rpm range. Of course, it is your choice. The 2800 will be quite the animal on 22.2 volts. I think you are perhaps underestimating the power you will have. Be sure to get some video! The truck is going to scream!

I have a box *full* of extra stock Traxxas parts...mostly lower control arms and bulkheads. :D


thx again for your help. I'll put my order in tonight or tomorrow morning.