I might start with all the same size wheels (and maybe add a large
front wheel later). Ordered some 5 inch casters today.
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The wheel is polyurethane, that is good. One but might be better if
the wheel had rounded edges, will see. The wheels can be replaced. It
uses Delrin bearings. I suspect that's better than ordinary ball
bearings that might malfunction because they will definitely get
dirty. Expensive casters probably keep dirt out of the bearings, but
I'm not ready to make that investment.
How the wheels will be attached is probably the major challenge. Once
that's accomplished, the wheels might need to be kept from turning
very far. The angle that the casters are set at might vary depending
on their position. The rear wheel can be fixed in position since all
it needs to do is pivit. That's good, because that means it can be
used as a drive wheel. Also possible is to use a scooter type
steering wheel for the front wheel.
Jillions of possibilities and complexities. How a caster wheel reacts
when it hits an obstacle is in question. Conceivably, the wheel can
be jerked to one side. But I don't think that's going to throw the
board off, because castor wheels probably don't work that way. They
can't work against force, since they turn freely. Therefore, they
probably can't jerk the board to one side or the other. Also, they
probably will be prevented from turning very far in either direction.
