Does this type of motor exist?

[sharpie_matt]

Hi all,

I don't know much about motors and am looking for a DC or AC motor for a project that does the following:
[ul]
[li]has a normal motor mode (ability to control direction and speed of rotation)[/li]
[li]is able to switch into a free swivel/coast mode with low friction[/li]
[/ul]

The motor is for a simple mechanism that allows a pendulum (a rigid rod) to be remotely "swung" up to some angle (perhaps with Arduino) through a motor locking itself to the swivel point, then released (i.e. "unlocked"), allowing gravity to take over and the pendulum to swing freely. I imagine there would need to be some ball bearing involved to reduce the rotational friction in the unlocked state.

Any and all help is greatly appreciated. I do have a bit of a budget for this project so cost isn't a huge deal.

Thanks so much!

 

[GregLocock]

Typically that is done with a magnet and a solenoid. Your proposal is over elaborate but possible. If I had to do it with a motor I'd use a small brushless DC motor, effectively replacing the solenoid and magnet. The trick in both cases is to drive at the resonant frequency of the pendulum.

Cheers

Greg Locock


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[IRstuff]

Your car air conditioning compressor has that feature, but it uses an electromagnetic clutch. On some cars you can hear it click as its energized so that the fan belt can turn the compressor.

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[BrianPetersen]

If I gather the original poster's intent, they want to drive the pendulum under power to a certain angle, and then let go of it to let it swing on its own.

I think the original poster is going to find that doing this will require a gear-reduction motor, and anything other than a complete mechanical decoupling of the gearbox output to the pendulum (thus requiring this mechanism to be back-driven) will interfere with the subsequent pendulum-action of the pendulum - whether it be by friction or by reflected inertia of the motor and gearbox.

If the intent is to build a grandfather clock, those are as described by GregLocock. There's a magnet (or a piece of iron) swinging with the pendulum past a tiny coil, and a suitable mechanism so that the electromagnet switches on and off at just the right time to keep it swinging once started ... and it's up to you to displace the pendulum far enough to the side to get it going. No bearings (other than on the pendulum shaft itself), no gearbox, no reflected inertia. But the little electromagnet that keeps it going isn't strong enough to get it started to full stroke in one swing, and it doesn't have to be.

If the intent is to build an impact tester of some sort, the ones that I've seen that have a mechanism for lifting the weight also have a mechanism to completely decouple the weight so that it drops by gravity without having to back-drive the lifting mechanism. An electromagnet is one way to do that. A mechanical pawl is another way.

 

[MJCronin]

Agree with IRStuff ..

Electromatic clutch is a well established technology and the way to go...

Do you have any idea of the motor size ?

You also state:

"up to some angle (perhaps with Arduino)"

Who is Arduino and why is he involved ????

MJCronin
Sr. Process Engineer

 

[IRstuff]

I hope you were just kidding

https://www.arduino.cc/[/URL]]WHAT IS ARDUINO?
Arduino is an open-source electronics platform based on easy-to-use hardware and software. It's intended for anyone making interactive projects.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

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[sharpie_matt]

Yes. An electromagnetic clutch is exactly what I'm looking for. Thanks.

I've been reading about them and am thinking about getting this one.

https://www.idicb.com/products/electromagnetic-clutches-and-brakes/clutches-clutch-couplings/type-fl

I'm thinking about 3-D printing my pendulum so that the swivel joint of the pendulum slides directly on to the armature hub of the above electromagnetic clutch. In most applications, one would secure a pulley or gear onto the armature hub but I figured I could just attach the pendulum directly, allowing it to be swung up by the motor to some angle when the clutch is engaged, then swing according to gravity when it is disengaged. Let me know if anyone has any better ideas.

I currently have this brushed DC motor (

https://www.pololu.com/product/2828)

that can be controlled with Arduino via a motor driver. Does anyone know if it is possible to use this motor with the above clutch? The motor has a 16 mm-long, 6 mm-diameter D-shaped output shaft which I don't think would work without some sort of adapter. People who have worked with clutches before: How does one get the right-sized shaft to use with a clutch? Can one 3-D print a shaft that can be fixed onto the motor D-shaft?

Thanks so much.

 

[BrianPetersen]

Looks to me like that clutch doesn't contain any bearings. (It's relying on the shafts that it is connecting.) You might have to arrange for your own bearings and shaft to connect to it. (edit: I think the input shaft is expected to pass all the way through, and then the output flange/shaft is outside it and is expected to have a pulley on it of some sort. Hard to tell if there are bearings between the input and output sides.)

I would make that shaft adapter by drawing it up and getting a machinist to make one on a lathe.