COUNTER WEIGHT 1

[swcaddesigner]

Calling on hard-core mechanical engineers. I am an ME but this is above me.

I have a rotating structure A that rotates at a slow 1 rpm. Attached to one end via a turn-table bearing I have structure B.

I do not want B to rotate and cannot fix it to any thing external. There will be a very small force wanting it to rock slightly which I do not want. How can I hold it stationary? A friend mentioned a Coriolis effect
or a flywheel with a motor attached to keep B stationary.

Any thoughts would be most appreciated.

 

[MintJulep]

Gyroscope.

 

[drawoh]

swcaddesigner,

I don't see how coriolis effect will help you.

Is A's shaft horizontal? How about putting a large weight on the lower side of B. This will not eliminate movement, but it will reduce it.

JHG

 

[hydtools]

Radio link rotary sensors to control motor to position structure B.

Ted

 

[MiketheEngineer]

How about a couple of big magnets - one on B and one off to the side?? Not sure what your coefficient of friction is??

 

[swcaddesigner]

Thanks All,
A gyro type is what I had in mind. I think it would work but not sure how to size a wheel.

Yes. Shaft A is horizontal. I have room for a large weight at bottom but as you pointed out it still could move slightly.

Magnet would work except anything off the sides,top or bottom is not possible.

Going back to the gyro idea. If I put , for an example and large heavy wheel (ever seen spin bike wheel?) mount it on the bottom of B and put a motor on it with the axis of rotation at a right angle to rotational shaft. Am I way off base?

 

[zekeman]

What about an arc solenoid with an arc plunger attached to B

 

[hydtools]

Something like a Ferris wheel? Structure B would have to have enough off-center weight to counter bearing friction.

Ted

 

[Compositepro]

A fluid reservoir with baffles could act as a damper.

Make B out of aluminum or copper and place a strong magnet close by. This will form an eddy current damper.

 

[msquared48]

Don't know if this a plan view or an elevation, but if it is an elevation, what about making B eccentric enough so that the bottom is heavier than the top, with a mechanism to let it turn relative to A?

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[swcaddesigner]

Hello again,
I have a new pdf showing the gyroscope cweight to keep B from rotating.

Guys , Will this fly?

Repeat
I have a rotating structure A that rotates at a slow 1 rpm. Attached to one end via a turn-table bearing I have structure B.

I do not want B to rotate and cannot fix it to any thing external. There will be a very small force wanting it to rock slightly which I do not want. How can I hold it stationary? A friend mentioned a Coriolis effect
or a flywheel with a motor attached to keep B stationary.

Any thoughts would be most appreciated.

 

[FeX32]

If you don't want B to rotate why did you attach the gyro to A?


Fe (IronX32)

 

[swcaddesigner]

My labeling is all messed up. B rotates at 1 rpm and we need A to be stationary,
My bad. Thanks so much for pointing that out.

 

[drawoh]

swcaddesigner,

I would sit down and carefully analyse your gyro befor I finalized this. I am not the expert on them. I worked one out a few years ago, and it did not work out very well. The gyro must be large compared to whatever it is stabilizing. You must deliver power to it. All the gyro does is increase the inertia. There will still be movement.

Don't confuse stabilizing gyros, and gyros that communicate with actuators. On gyro-stabilized platforms, the gyro is just a sensor.

If you can get electric cables to your gyro, you can get a non-electric cables to it. Cables, electric or otherwise, will prevent rotation of your device.

You could use slip rings to power your gyro.

JHG

 

[zekeman]

Look, you have to ask yourself what the allowable oscillation you are willing to tolerate.

If the axis is horizontal,as you show, then the overweight eccentric at the bottom seems reasonable, but the torque on A is steady due to bearing friction plus an oscillatory component due to variations in this torque. The heavier the weight the better the response. You could add damping effect by linking that weight to the bottom rather bolting and have it slide having an effective classical damper.

Your spinning mass does nothing, since the gyroscopic forces are in the wrong plane for correction, so the socalled gyroscopic effect does not work here.

If you truly need zero motion, which I am skeptical of, then the only thing I can think of is a closed loop induction plate rotating opposite, which will afford corrective motion plus damping. I don't think you want to go there unless you have lots of time and money.

Personally, I vote for the overweight bottom system.

 

[swcaddesigner]

To All,

You all are awesome and thanks so much for your valuable input.

Based on all the feedback a eccentric cweight might be the best approach. I can afford a slight rock. My best guess at this point stationary A should be 300 pounds. A counter weight hanging off the bottom and evenmounted a a slide might just do the trick.

 

[dvd]

That is a big gizmo at 27 ft diameter. What are the consequences if the bearing supporting A freezes up and A starts rotating? Anybody going to get killed or maimed?

You haven't given any options for alternate solutions, but it looks to me like the 27 ft disk should be supported off of a "turn table bearing" which has either internal or external gear teeth to allow it to be driven, and a stationary shaft allowed to pass through the center of the bearing which would support item A.

The shaft B is going to be big and require some expensive bearings. If you would provide a better explanation of what you are really trying to accomplish, then you might get some even better suggestions.

 

[IRstuff]

I don't think the gyro will do what you want. A gyro's input and output axes are perpendicular, so a motion in the plane parallel to the bearing race will result in a torque out of the plane. Can't see how that will help.

If you cannot hold A externally, are you allowed to drive against something external?
> An autocollimator or other sensor would detect the angle change and a PID loop driving a galvanometer or moving coil drive would hold A in place. > Another option is to have a rotor on A driving in the opposite direction of B; again, an autocollimator or other sensor would sense motion and either speed up or slow down the rotor to compensate for perturbations from B.

There are a bunch of variations on the above.

TTFN
faq731-376

 

[Walterke]

Is the movement of B constant or can it variate between 0 and 1 rpm (or -1 and 1)?

Either way, if possible you may want to consider putting an rod through A and supporting it on 2 (lighter) bearings in stead of one, this may reduce friction as there will be no rotational moment in the bearing. See added pic.

NX 7.5
Teamcenter 8

 

[racookpe1978]

Crawler tractor system with 4x (or 3x) wheels holding up "B" on the turntable. You'd have to power the motor driving the wheels.

Add a feedback (light sensor?) between B and a fixed object so the motors change speed as "B" moved w/r to the world reference frame.