Well I received the KNEX pulley tires and they are perfect except that the 3/8th inch rod is to big for them. So I exchanged the rods for 1/4 inch and they ride a little wobbly but will do. I decided to start assembling the rail system and get the carriage built. Next I plan on mounting the motors and do a trial. Bought some rubber bands to serve as pulley belts. We'll see how that goes.