42x19mm wheel does not fit on 120:1 Mini Plastic Gearmotor

Pololu Wheel 42x19mm page at pololu.com/catalog/product/1090 says:
"These wheels will also work in this orientation on the Pololu 120:1 mini plastic gearmotor 90-degree 3mm D-shaft output."
Actually, as it turned out, the wheel’s hub can get about 3mm of the motor shaft. I.e. the motor shaft gets only half way into the wheel’s hub. I would appreciate an advice on how to make these two nice products work together.


“In this orientation” refers to fitting the wheel with the teeth facing outward. The shaft on that motor (and on the Solarbotics motors mentioned) is too short to mount the wheel in its normal orientation.

- Kevin

Thanks Kevin for quick reply! I have tried “this orientation” yesterday. However, the shaft is still goes only 2/3 into the wheel’s hub. Does not look reliable enough to me. The shaft also needs some sort of spacer. Perhaps something like pololu.com/catalog/product/1971
It might be possible to drill a hole in the shaft and screw it from outer side of the wheel’s hub, but such delicate work is above my skills and abilities of my tools.

I will probably gave up on Pololu wheels and look for suitable LEGO wheels. There is a LEGO Wheel Adapter for 2mm Shaft (pololu.com/catalog/product/1001). The page claims this adapter fits on 120:1 Mini Plastic Gearmotor shaft. So I may cross my fingers and make another order…

Dear Pololu, it would be nice to have an adapter for the motor’s shaft for this wheels. It also would be nice to indicate clearly on the “Pololu Wheel 42x19mm Pair” page that the motor’s shaft is too short for this wheel.

Hello Misha,

The shaft isn’t too short for the wheel; there is no reason why the shaft needs to go all the way through to the other side of the hub. As long as you mount the wheel with the teeth facing away from the motor, pushing the shaft 2/3 of the way into the wheel’s hub should be sufficient to bind the wheel to the motor. Have you had any problems with the wheel falling off?

- Ben

Hi Ben,
Well… I do not have chassis ready to proof your confidence or my suspicion. A four wheel “off-road” buggy suppose to turn left and right by spinning wheels in opposite directions.
There is a deadline for this project which I do not want to miss. Thus, I would prefer to avoid possible surprises.

Does it feel like the wheel is loose to you? You should be able to assess the situation by seeing how much force is required to pull the wheel off the shaft. I expect that force to exceed the kind of forces typically experienced by the scale of applications this wheel and motor are intended for, but you could always add some glue to make the hold stronger.

- Ben

The wheel certainly does not feel as solid as I expected. I will try to use this motor with adapter and LEGO wheels.
In any event, thank you for help, Ben!

Just to finish the story… I have received “LEGO Wheel Adapters for 2mm Shaft”. First I tried to “push quite hard” as suggested on the page of the adapter. Well, I had no much success with 2mm hole and 3mm shaft. Then I tried heat. I have learned my lesson. No heat should be used with this adapter. Eventually I used 2.7mm drill to get adapter’s hole bigger and vice to “push quite hard”. This works. However, it is quite difficult to get the adapter precisely aligned to the motor’s shaft.
Finally, I should mention that a LEGO wheel feels solid on the adapter and whole the assembly seems to be good enough to be used as building block for a small robot.