Gear motor not running smoothly

[cyberfish]

I have a gear motor from Solarbotics (http://www.solarbotics.com/products/gm17/) using some alternative gears (http://www.solarbotics.com/products/51500/, the 51:1 one). It works, sort of. But I have 2 of them, and one of them spins a lot slower than the other (same inputs). Also, if I turn it off and try to spin the wheels by hand, the slow one feels a lot more "resistive". Not evenly, too (a few degrees of smooth spinning, and a few degrees of "resistive" spinning, etc), so I think something is wrong.

I opened it up, and took out the gears one by one, and tried to spin them by hand. Turned out, the last gear (directly connected to the motor's output pinion) doesn't spin smoothly. In particular, it's like half the gear is more "resistive" than the other half (half the circumference).

There is nothing visibly wrong with the pinion or the gear. I also tried spinning the pinion by hand and it feels smooth.

Any guesses on what is wrong and what should I do?

Many thanks!

[Choco_liger]

Hmm... this is just a guess but maybe you'll need to apply some sort of lubricant to keep it smooth.

Worn out gear perhaps?

[Soeren]

Hi,

In particular, it's like half the gear is more "resistive" than the other half (half the circumference).

There is nothing visibly wrong with the pinion or the gear. I also tried spinning the pinion by hand and it feels smooth.

Sounds like the hole for the axle may be a little off.
If the tolerances are fairly close, it doesn't take much offset to do that.

[cyberfish]

Worn out gear perhaps?

Hmm I hope not. I've only been running it for a few seconds in total. But I will try that if I can't solve the problem.

Sounds like the hole for the axle may be a little off.
If the tolerances are fairly close, it doesn't take much offset to do that.

That makes a lot of sense. Is there a way to fix that?

[dellagd]

Sounds like the hole for the axle may be a little off.
If the tolerances are fairly close, it doesn't take much offset to do that.

That makes a lot of sense. Is there a way to fix that?

drill? even a bit that is the current size of the hold and just put pressure on one side

[Soeren]

Hi,

Sounds like the hole for the axle may be a little off.
If the tolerances are fairly close, it doesn't take much offset to do that.

That makes a lot of sense. Is there a way to fix that?

I'd ask for a replacement. Just 0.1mm or less may be causing it and it would take drilling it larger (hard since the larger drill would be steered offset as well) and then a bushing to fill the empty space. But not having had it in my hand, or knowing your range of tools, machinery and dexterity, it's hard for me to judge on how possible it would be - but I wouldn't recommend it.

Having two of each, you could try with the one from the other box to be absolutely sure if that's the problem.
Not all bad though, it's often with these setbacks we learn a little extra and when you're done and it works, you know that gearbox intimately, which will help you later on with other gear related issues.

[dellagd]

oh, well if you can get a new one thats obviously the best choice 
I didnt know we were talking on such a small scale, my bad

-Dellagd

[cyberfish]

Yeah I may have to do that.

I'm trying to fix it by filing it down a bit.

[tim_wang]

Since these are molded plastic gears, you may be able to enlarge the shaft opening by hand. Start by rotating the gear in one direction, say clockwise, and mark the shaft opening when the gear starts to rub with a fine pointed marker. Keep turning and marking until you feel the rubbing stop. At this point you should have a band of marks by the shaft opening indicating where you need to remove material. Next gently inserting a drill bit that is just snug, and manually turning it against the side of the shaft opening that is marked to shave off tiny bits of plastic. The reason you should turn the drill bit by hand versus using a power tool is that with the latter it is very easy to take off too much material too quickly. Hopefully you only have to remove a tiny amount of plastic, so the gear can be pressed back onto the shaft. Good luck!

[cyberfish]

Well, before I read the last reply, I used a power tool to file it down, and I think I went a little too far. Guess I'm getting a new one .

[dellagd]

If it was defective, just get a new one, I mean, it was not ur fault!
no worries