Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

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.

Re: Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

Mount the cylinder on a pivot (like a lazy susan), and turn it with a motor, utilizing feedback from a gyro (or a camera if there's something to track on, like one of the goals). It requires some good code to make it work right, but teams have definitely done it before. I have a copy of the Behind the Design book for Aim High next to me, and there's some significant discussion in it about using and controlling a rotating turret for shooting balls.

Re: Rotation of a part independent of the base
 

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.

Re: Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

See part G :rolleyes:

Re: Rotation of a part independent of the base
 

If I understand you correctly, the mechanism you're going after is effectively this: https://en.wikipedia.org/wiki/South-pointing_chariot

It's ancient technology, but I'm sure the principles at work hold true. However, I'd be cautious with this design, as any slippage of the wheels while going over obstacles will introduce some amount of drift from the original direction.

I can't think of any other design that won't require sensor input. Your idea of floating in water has its problems aside from legality, seeing as any jostle will start it spinning. I don't see any use for a cylinder which points a certain direction but can't affect anything else.

I'm interested why you don't want to utilize a gryo/other sensor, seeing as they're by far to most mainstream way of monitoring direction.

Re: Rotation of a part independent of the base
 

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?

Re: Rotation of a part independent of the base
 

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.

Re: Rotation of a part independent of the base
 

If the bearing supporting the cylinder has no friction, then it will behave like you want. Also, if it has very little friction, and there is a lot of inertia in the cylinder, it will mostly behave like you want.

When I was a youngster, gyroscopes were mechanical....they had a part that spun very fast, and it was mounted in a gimble, on low friction bearings. Look it up. Maybe you could do something like that.

But my guess is that you might be able to think of other ways to play the game, that don't require so much fun design and fabrication work.

Re: Rotation of a part independent of the base
 

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

Re: Rotation of a part independent of the base
 

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.

Re: Rotation of a part independent of the base
 

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?

Re: Rotation of a part independent of the base
 

There have been USB breakout boards included in the KoP in the past that let you wire up analog/digital equipment and read it in like a joystick. I haven't looked yet, but I know an ADALM1000 was included in the KoP this year, maybe you can do it with that?