To build a conveyor belt requires a few parts; motor, bearings and belt.
Polybelt.com for a 40 inch long by 2 inch wide belt
vxb.com for bearings
sciplus.com for a motor (I used #40588, a gear motor intended to move automobile seats)
Files for the 3d printed parts are available at:
Start by making a "roller," 2 inches wide with a 2 inch diameter. I used a 1/4 inch diameter wood rod for the axle.
I placed a couple of "guides" to hold the motor mount and a bracket to adjust the tension on the motor.
Friction fit the 2 inch wide by 2 inch diameter roller (different axle diameter from the other roller) onto the motor. Set the motor on the motor holder.
Put the belt on the non motor roller before securing the roller to the base.
If you're smart (not like me), you'll put the roller guides on the rollers at this step--to keep the belt from slipping off.
Add the "belt guides" using acetone or super glue.
Mount the servo horn to the top of the boot (backs side, where the holes are).
Screw the servo horn to the servo motor (of course you need to have the servo in the "boot down" position).
Slide the servo motor into the motor holder.
Put the motor holder lid on and run machine screws through the holes.
Attach the motor to the top of the "servo tower."
Route the servo wires through the hole in the servo tower.
Place the photocell and led in their holders, then fasten them to the base.
Add the acrylic shields to the sides.
The base (24 inches by 9 inches) should be raised 5 inches with two wood supports.