Kalio

Hi everyone! I just got a RC18B2 brushless RTR and everything seems to work great except at low to medium throttle, the car stutters about every second, as if the throttle was being cut very briefly or something was getting snagged. I'm pretty new to RCs, but I can't seem to find anything mechanically wrong with it. Belts and tension seem good, slipper clutch seems to be adjusted correctly, even tried remounting the whelels (it doesn't seem to like having them on too tight). If I roll it by hand everything is smooth, nothing seems to be snagging or anything. Once I apply more than medium throttle it runs just fine and it can hit top speed with no issues.

Sooo I've been searching the Internet far and wide for this problem with no reported solution. It seems like the main culprit could be the ESC, but I'm having a problem getting that to reset, the SET button doesn't seem to work no matter how closely I follow the directions. I put in an email to AE support, maybe there's something wrong with the ESC..? Anyway, looking for help if anyone has any ideas. Thanks!

toddmac

When you say slow or medium throttle do you mean at very slow speed?

My first diagnosis is ESC/Motor "cogging", which is a very common thing that happens with sensorless motors. Reason for cogging is that the motor gets more or less stuck between the motor magnets. In a two pole motor, the stator will bounce back and forth between the poles and runs pretty jerky, trying to figure out where the stator is compared to the poles. In a sensored motor, the motor has sensors so that the ESC always knows where the stator is in relation to the magnets, eliminating the cogging virtually 100%. Sensored motors typically way more expensive and typically don't come stock in a RTR car.


I would guess with the information that you given that it is just a sensorless motor problem. Actually not a problem, its just how they work. Nothing you can do about it, but doesn't affect the performance of the motor, really its just an annoying trait to the motor.

Kalio

Yeah, I have read a little bit about cogging with sensorless motors such as this. I suppose it could just be that. I was just surprised it still happens even at moderate speed, say, 30-40% throttle. Looks like sensored motors are hard to come by for the 1/18 scale (and expensive too).

I finally had it out for my first run yesterday, now that the weather finally cleared after nearly a week of rain. It was a blast. I didn't notice the problem nearly as much out in open space. I could still hear the engine power cutting off at lower speed but the effect wasn't nearly as noticeable as it was in doors at really slow speed.

Kalio

I heard back from AE and they think it might be something with the speed control. Unfortunately I can't get in to calibration or even configuration mode at all with the ESC, so maybe they can help me with that problem first.

Here's a quick 30 second video of what the car is doing:

('Doh, I'm not allowed to post links without a minimum number of posts first.)
YouTube: .../watch?v=lTmPdN4289M

toddmac

....yeah thats strange

Kalio

It looks like the problem really is simply motor cogging. I just picked up a RC10B4.2 and it does the same exact thing, though not quite as easily / frequently at least. I was finally able to figure out how to calibrate and set up the RC18's ESC (no thanks to AE support.. their instructions are definitely not correct) and that didn't make any difference (though it was nice to finally be able to configure it).

Oh well, not a big deal, that's just how sensorless motors are it seems.

2uzferunner03

Are you running an nimh battery? If so a 2s lipo will help

Kalio

Yeah, only had a couple of nimh batteries for the RC18. The RC10B4 I just got came with a pretty small 2s Lipo though, seems like it'll fit in the RC18. I'll have to try that sometime!

eR1c

iTrader: (2)

this would be my guess too.
I've had this issue w/ 1/10th and 1/12 scale vehicles ...but am sure it is the same w/ smaller scale. Can you go down a pinion size or two and see if this changes anything? The fix for me has always been going to a slightly smaller pinion size. It's as if it is taking just too much torque that the motor doesn't have to get the gears moving.

Kalio

Yeah, it seems it really was just cogging all along. My newer 1/10 electric car (RC10B4.2) also exhibits the exact same behavior (though not as pronounced), so I'm assuming this is the case with most sensorless smaller scale motors. This was my first RC car so I just wasn't used to it. It's been a while since I spent any time with this car now since I've pretty much devoted all my tinkering and practicing to the B4.

As for issues with the ESC, it just seems to be really finicky about entering setup mode. I was able to finally configure it how I wanted. Since the instructions were quite wrong (even AE admits this), it took me a while to finally figure out how to get that to work (and even following the proper instructions it's a little tricky, sometimes the button gets stuck too).