Take a square wheeled bicycle and a track with just the right bumps and you can get a smooth ride.
The track is a sequence of bumps which are inverted catenary curves. Tracks interlock so you can buy more than one and join them. The bumps are just the right shape for our square wheeled bicycles to ride smoothly.
A ridge helps keep our bicycles (actually quadricycles) on track.
We have 2 styles of square wheeled quadricycle. Each works with the catenary track.