Foam Combat Robot Wheel Hubs

I designed these to replace the metal foam wheel hubs like the ones available from Palm Beach Bots. (For our 3D printed combat robot tournament the metal ones are not allowed.) Also, these can be used on many different kinds of motors with shafts diameters ranging from 7mm to 3mm. 

They are held on with the washer on one side and the locking nut on the other. (See the pics.)