A prototype is to show that it works. And that's all.
There is no minimum performance or power requirement. It's just to implement the principle.
When Diesel invented its combustion principle, it did not start by making an aircraft carrier engine to illustrate it.
If the principle is good, whether the prototype is small, medium or large, it will work. And the less there are complicated parts to make, big or small, the less expensive it is. A nut shell floats; a wooden shell of the same shape but 3 m in diameter, it floats the same but it is not the same price.
A compass shows you the north; a giant compass of 10 m in diameter, it is not sure that the "needle" moves a lot with the friction due to its weight.
With just one wheel it won't work, or you have to invent another system.
We create the difference between the wheels, on straight lines, and not on a single wheel. On a single wheel we will always have a balance
If the wheel works, the chain will work; it is only the "fabrication" of a straight line movement.
If you look at the drawing of my wheel, it IS unbalanced.
If it would have been possible and easy, someone would have done it long ago
At this rate, we do more.
Check out the sites on the Stirling engine. You will see functional models.