Gyro stabilized two-wheeled toy : Why the gimbal?

[Swamp Thing]

Will this toy stay upright if we get rid of the gimbal and fix the gyro's rotation axis w.r.t. the chassis?

 

[FactChecker]

The way they have it, any tendency to tilt is resisted by the gyroscope, which freely rotates on the gimble. If you remove the gimble, a tendency of the board to tilt sideways creates a desire for the gyro to tilt forward or backward. That is then resisted by the fixed platform that the gyro is on and the resistance force makes the gyro want to tilt sideways. So the gyroscopic stabilization is defeated.

A simple experiment shows what happens. If you hold a gyro in your hands and try to tilt it, you feel the resistance to that tilt (initial tilt) and a desire of the gyro to tilt in another direction (secondary tilt). But if you brace the gyro so that it's desire for the secondary tilt is stopped, you will not feel any unusual resistance to your initial tilting. It would feel as though the gyro is not spinning at all.

 

[Swamp Thing]

But if you brace the gyro so that it's desire for the secondary tilt is stopped, you will not feel any unusual resistance to your initial tilting. It would feel as though the gyro is not spinning at all.

I'm finding it hard to visualize that, and I don't remember noticing it when I last played with a bicycle wheel gyro (which was a long time ago, admittedly).

I'll think about it a bit more and get back.

Thanks.

 

[Swamp Thing]

I'm beginning to get it -- I think -- based on adding the vector angular momentum that the new constraint would try to produce, on top of the original angular momentum of the spinning gyro. When we add the extra constraining torque, the resultant shows that the whole thing would tend to tip over.

 

[anorlunda]

This may help. Especially the demo at 3:09

 

[FactChecker]

I'm beginning to get it -- I think -- based on adding the vector angular momentum that the new constraint would try to produce, on top of the original angular momentum of the spinning gyro. When we add the extra constraining torque, the resultant shows that the whole thing would tend to tip over.

Yes. I have a gyro where the gimbal can be braced against a table to prevent any lateral turning. When I push it forward, the desire to rotate laterally is exactly opposed by a force from the table. It feels like it is not a rotating gyro at all -- just rotating forward with no unusual opposition.