Customizable wheel for common toy gearmotor

thingiverse

(Picture note: The filament and the motor I bought surprisingly share the same color - that's just a coincidence. However, I made sure to get it from eBay.) This wheel precisely fits into those little yellow plastic motor+gearbox combos available on eBay at an incredibly low cost. After printing, you'll likely need to gently hit the bore hole with a small file to ensure a perfect fit - but then you're all set to go. You can choose to add some extra grip by dressing the rim with your preferred traction material (such as a rubber band, electrical tape, or silicone goop, and so on).