The rectangular frame is welded from some round and quadratic steel pipes. Two brackets for holding the wheel are welded onto the bottom side. Two saddle posts are welded exactly above the pedal bearings. Two diagonal smaller steel pipes are stabilizing the rectangular frame.
The pedal bearings
The pedal bearings are custom made slide bearings: A steel shaft rotating in two brass bushes. They are supported by a triangular steel plate construction and screwed to the frame. The chain can be tensioned by a simple tensioning bolt. A pinion is mounted throug a custom made aluminium bracket.
The wheel is a used motorcycle wheel with two single pinions screwed to it on either side.
Unicycling saddles are stuck into the saddle posts and fixated using a commercially available seat clamp.
The pedals for both riders are directly connected to the central wheels, one chain on the right side, one chain on the left side. The chain tensions can be adjusted seperately by chain tensioning bolts. So we can get a backlash-free (or nearly free) drive system.