Print (3) bearing supports and install 6x19x6 mm bearings.

Print one "belt spool motor" and one "belt motor bearing." Glue or melt the "belt motor bearing" to the end of the "belt spool motor."

Print one "belt spool" and two "belt motor bearing" pieces. Glue or melt the "belt motor bearing" pieces to the ends of the "belt spool." Wrap the belt around the spools, then place the shaft ends into the "bearing supports." Place the motor in the "motor holder" (secure with 3mm screws). Adjust the bearing supports until the belt is in reasonable tension, then secure to the plywood base using wood screws.