Curious 36120 problem - RC-Monster Forums

Gustav · 05:46 PM

Got my LST running today (thread to follow with build pics and details),anyhoo,got a problem with the 36120.setup is 36120,1950/10(1307kv),8s lipo.
Basically it cuts the motor hard at a certain rpm,it's definately nothing to do with the truck,ubec,radio,lvc etc.It does it in forward only or in forward/brake/rev. mode.

It cuts so hard that out of the truck the motor jumps about an inch.I'm having to run a high load to stop it happening,anything below 11:1 final drive on 8s it will cut at WOT/high rpm.This is in a 13lb LST so it's a fair old load.I can't see that it's hitting the 42K rpm limit since it will even do it on 16 cells unloaded.Is it possible for 16 nearly flat cells to send a 1307kv(loaded rating) motor to 42000rpm unloaded? I seriously doubt it (that would need around 2200 unoaded kv)but i guess that is the question.Any ideas WTF else it could be? It runs great if i keep enough load on it,smooth,cool and seriously quick.

coolhandcountry · 04.02.2006, 07:00 PM

Why exactly do you mean by cuts the motor?

Gustav · 07:12 PM

Sorry,should have explained that,it's as if it suddenly cuts the power to prevent it reving any higher,it acts like a very hard cut rev limiter,it's very sudden like lifting off the throttle very quickly for a brief moment.

pcnutz · 04.02.2006, 08:44 PM

I had problems with a 9918 where randomy if you juiced it it would lose position and make a loud clank in transmission and make the motor jump, sounded like my trans was going to bust up

Serum · 04.03.2006, 05:22 AM

Dumb question;

You didn;t used the LVC with 16 cells right? with 8S, it seems loogical it hits the 42k limit, but with 16 cells.. Hmmmmm...

Perhaps a reveicer glitch..

Dafni · 04.03.2006, 06:22 AM

Please give it a try without the LVC.
I think I know where the wind is blowing.

What LVC are you using?

If you can, hook up a 2P lipo setup.

But first of all, give it a short try without the LVC and report back.

coolhandcountry · 04.03.2006, 07:04 AM

Do you think he is having the same problem you have daniel? The motor is dropping the voltage to far on the lipos.

Dafni · 04.03.2006, 07:13 AM

Well, it's not really a problem, CHC. It just shows the batteries are not up to the task. A 2P setup will cure this. And if I have the throttle at 75%, it works fine even on a 1P setup (altough, admittedly, the Lipos suffer a bit) Just for the record :)
More testing is neede here. Be on the lookout for a detailed thread!

Gustav, a 1:11 reduction on a heavy MT will pull some serious amps. Might drop your voltage so the LVC cuts in.
Just check without the LVC and we'll know more.

Gustav · 09:37 AM

Yeah i'm not using lvc or ubec to keep these out the picture,so that's ruled out.
The reason for the high 11:1 gearing was it seemed less noticeable yesterday on higher gearing. Tried 14.75:1 through to 11:1 today with same results regardless of gearing.

It can't be 42K limit since it does it on 16 cells too.It doesn't seem to be a radio glitch either as it reliably/repeatably does it at anything above 80% epa,and there's no other glitching to speak of.

Below 80% epa it runs smooth but above that it glitches at full throttle.

So i'm thinking maybe a timing issue,although it runs smooth and cool up to 80% throttle.I'm a bit stumped on this one.

Only other thing i can think is batteries or wiring issue (perhaps not enough amps available or a wiring/bad solder joint issue).Lipos are rated 66 amps continuous.

Dafni · 04.03.2006, 09:46 AM

Can you hook up a 2P setup? To get the amp draw out of the picture.

Gustav · 04.03.2006, 09:53 AM

Only got the one pair of packs at the moment so unfortunately not. It will do it on 16 cells too but only with the wheels off the ground,runs OK on 16 cells at full throttle even on a high gearing,it seems more like a certain motor rpm where it happens rather than current draw.

Could a bad solder joint cause this syptom in your opinion,i might re do the wiring tonight.

pcnutz · 04.03.2006, 10:19 AM

if you figure out how to fix the lose of position or timming issue lmk, if you do not, buy a better controller

Serum · 04.03.2006, 10:24 AM

I don't understand it anymore (my bad) does it work on 16 cells or does it have the same problems?

Gustav · 04.03.2006, 12:42 PM

It will run on 16 cells fine under load,but with the wheels off the ground it will do the glitch thing when it reaches a certain RPM.That's what's confusing me.

It does seem like a timing issue or loss of position when it reaches a certain rpm.I can't open the program for the programming cable even though i have microsoft office and winzp.i'm wondering if the 'slow power' feature is on.It reduces rpm limit and is for <20k rpm set ups.It says this feature is on by default on 24MHz controllers.Is the 36120 24MHz?

I hate to give up but this is realy doing my head in,i'm contemplating trying to return it and buy a 32.170W instead,it's huge but i have a seperate upper deck for the esc so it would fit.

nl12 · 12:45 PM

I would not think it to be an amp draw issue since he said the motor cuts out unloaded as well, it couldnt be pulling that many amps unloaded. I would try reprograming the controler. Maybe you have a different kv motor than you think and it is hitting the 42000, maybe lehner mismarked the motor, stranger things have happened. Try the motor with a different controler like a 9920 unloaded and see if it does the same thing, if it does then something is definately wrong with the motor, if it works fine--maybe its your controler, maybe it is the mismarked kv issue. I dont know how to test the kv of a motor if anyone does that could help eliminate one potential problem.