This gadget is to move a wheelchair in place for fitness purposes. It consists of 2 rollers made of tubes that carry the wheelchair, a chain and a flying wheel that extends the movement of the user. To enter or more precisely climb the gadget, there is a brake and a ramp. Unclimbing or leaving the gadget is more sophisticated: With the gadget's brakes on, the user has to nod the wheelchair to gain momentum and move backwards in a jumpy style. Not easy but it works. Resistance for the training effect occurs by friction, e.g. between the rubber wheelchair wheels and the roller tubes. The gadget here is for airless wheelchair tubes.
Step 1: Find a Clamping Set and a Tube
The roller tubes are fixed to the axles. Find a clamping set (de: Spannsatz, maedler.de, hreiter.at) and a tube thats more or less wide enough so the clamping set fits inside (posamentir.at, fixmetall.at) without lathing. The tube can be some 0.1mm different but not much more. My axle is 20mm, I don't know the tube's diameter unfortunately.
Picture: on the right
Step 2: Make the Cogwheel on the Axle
Find a small cogwheel from a bike. Find a clamping set with a small diameter. Lathe an adapter like in the drawing and leave a 0.1mm flange for the cogwheel not to fall off. Assemble and fix.
Previous pic left side
Step 3: Fix Cogwheel on Flying Wheel
Find a flying wheel from a conventional standing-bike-fitness (de:sochn) and weld another cogwheel from a bike onto it. Weld or find a chassis for the flying wheel and a board for the rollers.
Step 4: Add Brakes
Add a brake from a bike and combine it with a quick release skewer (de:Schnellspanner). Place it near the user, nearer than me, maybe on the other side!
Step 5: Add Stabilisation Rollers
Again, find rollerbearings and a tube that fit, I had to use a lathed adaptor.
Step 6: Build a Ramp
If the roller tubes are placed further away from each other, then stability in operation is better. The narrower they are, the easier it is getting on and particularly getting off.
Build something to cover the harmful moving parts.