Gears slipping on reverse

[robo555]

I built a new CC-01, stock with ball bearings, I haven't taken it outside yet, just played in my apartment. Yesterday my friend had a go as well.

Now, going forward works fine, but when going in reverse, the motor spins but the wheels and driveshaft don't turn, and it sounds like the gears near the motor is slipping.

I opened the gears cover and didn't spot anything broken. I did noticed the cover is the only thing keeping the gears in place, i.e. with the cover off, the gears will pop out when the motor spins, so could the cover be somehow not holding the gears correctly?

What's the problem and how do I fix it?

[monkeyracing]

Yes. The easiest repair is to get some longer M3 machine screws and nuts and drill through the chassis. The screws go from on top, nuts underneath socking everything down, nice and tight. Option B is to attempt a repair of the threads. Go with plan A.

[robo555]

Thanks for your help, as you can see from the pic, I've shimmed the gears with masking tape to minimise play, and used screw + nut for the middle screw on the engine cover since there's already a hole at the chassis for that screw. It didn't fix the problem, but found the real culprit:



The first step of the build instruction was to screw the motor to the motor mount, but there's no threads in the motor so it's barely attached to the mount, i.e. the two screws will fall off just by shaking the motor by hand. This means the motor has tons of play when it's spinning and disengages from the gears. I'm using the holes labeled '16' as per instruction.

This is the stock motor, how am I suppose to attach it tightly to the car? I believe the screw + nut would not even be necessary if the motor is securely attached.

[aircooled]

If the motor has no threads to be mounted (which I have never seen), the whole thing won't work and the motor need to be replaced.
Trying to fix this in any other way will only lead to more damage elsewhere.

[robo555]

Mmm...that's strange then, since it's the stock motor from the kit. I just checked again, it's the correct M3 6mm screw, but it slides in and out of the motor's mounting holes, doesn't seem to have any threads.

[Tonysmini]

I had the same thing in a Tamiya supplied motor last year, maybe they had a duff batch supplied.

The stock 27t is too quick if you ever want to go crawling. Try a 55t motor instead.

[robo555]

I've got the motor correctly mounted to threads now, fixes the reverse problem. I've left the shims in but still using standard screws for the engine cover because screw + nut takes too long to unscrew.

I'll mostly be doing dirt/trail stuff, very little actual crawling. I would like my truck to be able to keep up with a bicycle, i.e. ~15-20km/h. Would you still recommend a 55T? What's the top speed of a 55T, do you think a 35T is better for me instead?