Rotation of a part independent of the base

[KyloRen42]

Excuse the MS paint, but:


Is it possible to isolate the yaw of the cylinder on this prism?
More clearly: Is there a mechanical way to have the rectangular prism rotate but the cylinder will not follow it?

For example, the entire system is facing north. The rectangular prism (robot) turns south, but the cylinder has not rotated at all. For any other non-rotation movement, the cylinder obviously still follows. So if it drives north, the cylinder will stay attached and come north with it.

edit: Please purely mechanical, with no gyro sensors etc

[rzoeller]

Easiest thing I can think of is to put the cylinder on a Lazy Susan, and hook it up to a motor to turn. Mount a gyroscope to the cylinder, and use something like PID to drive the rotation of it back to zero continuously.

[jimbo493]

You could use an accelerometer/gyro like the navX board to track the prism, and have a slew ring with a motor to turn the cylinder opposite of the prism. Assuming that the prim is the robot and the cylinder would presumably be a mechanism.

EDIT: rzoeller beat me to it

[cjl2625]

Well, I guess you could put a gyro on the cylindrical component, and assuming the cylindrical thing is on a motor, have it on a closed-loop system to keep it facing at a constant angle.

But maybe that's not what you're looking for if you want something purely mechanical.

Edit: someone beat me to it

[KyloRen42]

Originally Posted by cjl2625

Well, I guess you could put a gyro on the cylindrical component, and assuming the cylindrical thing is on a motor, have it on a closed-loop system to keep it facing at a constant angle.

But maybe that's not what you're looking for if you want something purely mechanical.

Yes, I am looking for pure mechanical. The only way I can think of is to have the cylinder floating on a small reservoir of water, but I am pretty sure that'd not allowed.

[rzoeller]

Originally Posted by KyloRen42

Yes, I am looking for pure mechanical. The only way I can think of is to have the cylinder floating on a small reservoir of water, but I am pretty sure that'd not allowed.

Without strengthening the Earth's magnetic field, I can't think of a better way.

[jimbo493]

if you had a swerve type drive you could link of a steering module in some way shape or form, but it would only work in certain turning situations, and is pretty complicated. The best way is probably to just use a gryo, it sound complicated, but is way simpler than a mechanical system, which in itself is not very feasible

[menns]

Originally Posted by KyloRen42

Yes, I am looking for pure mechanical. The only way I can think of is to have the cylinder floating on a small reservoir of water, but I am pretty sure that'd not allowed.

I was going to suggest floating it in mercury but aluminum and mercury don't get along so well.

[KyloRen42]

Originally Posted by menns

I was going to suggest floating it in mercury but aluminum and mercury don't get along so well.

But hey, maybe the reservoir wouldn't count as a switch or contact!!!

[rzoeller]

Originally Posted by KyloRen42

But hey, maybe the reservoir wouldn't count as a switch or contact!!!

See part G

[KyloRen42]

OK maybe we will do it with a gyro then. How would I keep the gyro accurate after we are bumping around over things like the rough terrain, etc? Would it stay accurate within say, 2 degrees over the course of a match?

[rzoeller]

Originally Posted by KyloRen42

OK maybe we will do it with a gyro then. How would I keep the gyro accurate after we are bumping around over things like the rough terrain, etc? Would it stay accurate within say, 2 degrees over the course of a match?

It will drift - the exact amount will depend on how much jostling around you do. I would recommend adding a potentiometer or some sort of feedback mechanism (even just a button based trim control) to correct for when it does drift, i.e. keep a counter that you add/subtract from the reported value based on driver feedback.

[KyloRen42]

Originally Posted by rzoeller

It will drift - the exact amount will depend on how much jostling around you do. I would recommend adding a potentiometer or some sort of feedback mechanism (even just a button based trim control) to correct for when it does drift, i.e. keep a counter that you add/subtract from the reported value based on driver feedback.

If you've used gyros before, could you give me an example of how bad it could drift?

[Jon Stratis]

Originally Posted by KyloRen42

OK maybe we will do it with a gyro then. How would I keep the gyro accurate after we are bumping around over things like the rough terrain, etc? Would it stay accurate within say, 2 degrees over the course of a match?

I would just add in a manual adjustment knob on the driver station - let the second driver adjust it one way or the other as needed during the match.

[KyloRen42]

Originally Posted by Jon Stratis

I would just add in a manual adjustment knob on the driver station - let the second driver adjust it one way or the other as needed during the match.

Is there somewhere we can buy a USB knob or something, or do we have to make one? How would you do something like this that could be recognized as a controller by the driver station?