Premium 4WD Smart Robot Car Chassis Platform Kit for Arduino, Raspberry Pi, MicroBit - DC Electric Motor with Plastic TT Wheel, 3-6V Dual Shaft Gear Motor, Magnetic Gearbox Engine (Black)

I bought this as a project base for my grandson & me. The wheels would not fit on the motor shafts. The radiused holes in the wheels are too small for the radiused shafts. Poor Chinese quality control strikes again... I asked for new wheels that had been pre-fitted at the factory. They asked for pictures of the bollocked wheels . I sent pictures. Two days later they refunded my money. 3 stars because the refund was quick. Zero stars for the product... Also, there is no encoder, just slit disks that did fit on the motors. Mfg's blurb says encoder...

The actual metal chassis is fine, however the motors and wheels are terrible. I suspect these motors were drop-shipped or resold off of some cheap manufacturer. They are sold on nearly every platform, and despite buying multiple versions over the course of my project, they all have significant problems that reduce efficiency and controllability. One motor even fell apart completely, making it useless. Aside from the motors, the wheels have too small of a hole to fit the motors. I had to drill into them to make them wider, and still their fit was far from perfect. I strongly advise you do not buy this kit, or any motors that look similar, and do your research to purchase better, high quality motors.

I had the same problem where the wheels wouldn't stay on because the holes in the frame are too small. I thought about drilling them out but that seemed like too much work. Putting the motors on the outside solves the problem and gives you more room for the encoders inside.