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Trying to create rotating device/minimum speed. Could use some advice!

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schizotypal_boy

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Hi there..

So, I know pretty much nothing about electronics but have been trying to create a device that will rotate a painting, as slowly as actually possible..

I picked up one of these https://www.mfacomodrills.com/gearboxes/918d_series.html (918D1001ME) Ideally, I would have a motor this size, that could have it's speed regulated by something like this: **broken link removed** but due to the voltages not being compatible, this seems not possible. One person mentioned buffering the circuit with a transistor but I tried to look into that and it seems way beyond me! Am I right in thinking I can use the speed regulator with this motor, and it would be possible to slow it down as slow as it can go? **broken link removed** (148:1 Lge Gear Box)

I would hugely appreciate any thoughts, ideas, links regarding this.. I literally want to fix a motor to the back of a 50 x 50cm painting and have it rotate counter clockwise at minimum possible speed.. and I don't have much time left! :S

Thanks for reading and I look forward to hopefully a simple solution!

C.
 
If your electronics knowledge/experience is very limited and you 'don't have much time left' you are unlikely to be able to build a control circuit yourself and will have to find an off-the -shelf solution. So I'd suggest using a motor with a large-reduction-ratio gearbox driving a second (and possibly even a third) large-reduction-ratio gearbox.
The Re80 motor in the first link is, AFAIK, quite high revving, so even if you could get its speed down to, say, 600 rpm the output shaft of the 100:1 gearbox would make one rotation in 10 secs. I'm guessing that would still be too fast?
 
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Before you go anywhere, you need to figure out the torque required. A spring scale or adding weights at the max distance from the center with the painting so it can rotate freely on a bearing of sorts would be a first step. My math is rusty to try to estimate the torque.

Here https://hurst-motors.com/lyg55geared.html is a 200 OZ-in AC synchronous motor that can rotate at 0.42 RPM. Synchronous motors work off of AC and their RPM is determined by the power line frequency. They need a capacitor to work and they are reversible. Watch the mains frequency and the voltage. I've use the 40 OZ-in motors from this company.

200 OZ-in is a pretty powerful motor
 
Thanks so much for your feedback on this..

I think one rotation in 10 seconds is still too fast, yes. Difficult to determine exactly what the best speed would be, but too slow is not so much an issue, too fast ruins the idea completely. I think perhaps one rotation per minute..

Not sure how to measure torque, but will look into it.. thanks!
 
Torque is essentially Force * Distance.

Some other ideas. A lazy suzan mechanism driven by a friction wheel.
 
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The turntable drive in a microwave oven rotates at ~ 2-3 rpm and IMO should have enough torque for your purpose. It is also low noise (unlike a high-revving geared DC motor). Perhaps that could be used to drive a simple reduction gear/pulley system if still too fast.
 
The turntable drive in a microwave oven rotates at ~ 2-3 rpm and IMO should have enough torque for your purpose. It is also low noise (unlike a high-revving geared DC motor). Perhaps that could be used to drive a simple reduction gear/pulley system if still too fast.

Hi Alec_T I also was going to suggest a microwave turntable motor, but they probably won't have the torque. I used one (2 or 3 RPM) in a tumbler and was disappointed how little torque it had compared to even a small DC gearmotor. The tumbler had to be quite well balanced.

If more torque is required he can get a 100:1 or 200:1 DC gearmotor and if still too fast add a large pulley and belt?
 
If the 50cm x 50cm painting is mounted at its centre of gravity on a low-friction bearing (e.g. ball race) I'm guessing it would need about the same torque as a microwave turntable to rotate it.
 
If you want or need a canned solution, depending on your location and what you want to spend I would look at a ready to go motorized turntable. Something like this from McMaster Carr but again I don't know your location. Regardless, I am sure they can be found less expensive in assorted speeds (including variable speed) from a host of sources. Click Motorized Versions in the link.

Ron
 
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look here https://www.mcmaster.com/#light-duty-gearmotors/=h0nyjw at the ac motors, not controllable, but you have a choice of speeds scroll down to the Synchronous AC Gearmotors or on down to the DC motors which would be controllable by varying the DC voltage.
Your choice may depend on how much room you have behind the painting and how you can mount the painting, but if it's balanced, torque may be minimal and you would need to worry about is the weight of the setup and the forces of gravity.
 
KISS,

Torque is essentially Force * Distance.

Not so fast. Work or energy is force times the distance travelled. Torque is radius times the sin(θ) of the force, where θ is the angle between the force and the radius. Torque is a vector, energy is not.

Ratch
 
Something like this should work.

**broken link removed**

Maybe you can find one locally.
 
look here https://www.mcmaster.com/#light-duty-gearmotors/=h0nyjw at the ac motors, not controllable, but you have a choice of speeds scroll down to the Synchronous AC Gearmotors or on down to the DC motors which would be controllable by varying the DC voltage.
Your choice may depend on how much room you have behind the painting and how you can mount the painting, but if it's balanced, torque may be minimal and you would need to worry about is the weight of the setup and the forces of gravity.

So I was pretty set on getting the compact DC gear motor, 2nd one down.. 1.3 rpm.. but then they refused to take the order as they don't ship overseas to anyone who is not a 'trusted customer' due to 'complicated export laws'.. Annoying. I was looking at this: https://www.electro-tech-online.com/custompdfs/2012/04/seriesDC-800.pdf

but don't understand if it will support the weight.. 2.17kg (217g) I found this: https://www.linengineering.com/flash/Calculator.swf which is pretty neat, but still don't understand the conversion.. I've converted 60 oz-in, which seems to be the value that the motor will support I think.. but can't tell if 217g is supportable.. ?
 
That is rated torque; not the same thing as the weight the shaft can carry.
Are you planning to support the painting directly on the motor gearbox output shaft? If so, you will clearly need a robust gearbox to handle >2kg. IMO it would be better to support the painting on a substantial ball-race and use e.g. a belt drive to rotate it. That would enable a light-duty motor/gearbox combo to be used.
 
Aahh.. yes. My bad. 2170g!

ball race/belt drive? It's been mentioned before, using pulley system.. that sounds more complicated to put together, for me, so I am reluctant to try it and potentially failing, though it does seem like a good way to take weight off the motor..

I'm looking at this motor and thinking to power it with 6v, would that deal with the 2.17kg ok?

919D30001LN (bottom in the list)

https://www.electro-tech-online.com/custompdfs/2012/04/919DLN20series.pdf
 
Well the torque looks adequate, but the spec says the gearbox has sleeve bearings. How long they would last with a > 2kg lateral load is an unknown quantity. To quote Clint Eastwood, "Are you feeling lucky?"
 
Intuatively: Circles and squares would be fine. With rectangular, and draw a square centered. At 1/2 the square side + 1/2 the (length-(the square side)) call this d1, you'll have a force of m1g acting there. The mass is the excess material and g is the force of gravity. So the motor torque must be greater than d1*m1g. Not sure. I'd have to draw it. This does assume that the painting is homogeneous and has no frame.

In any event, the excess non-symetrical mass acts at a distance the moment of inertia away on both sides. So when the system is horizontal or verticle ther is no tendency to rotate. m2d2=m3d3.
I do know this when I was asked to calculate a weight for his non-symetric mobile.
 
To quote Robert De Niro: "You talkin' to me??"
You're losing me there,
but the painting is square (50 x 50cm), on a stretcher, there is no frame on the exterior of the canvas. I have a bit of wood secured diagonally within the stretcher, which I was thinking to use the central point of, to fix the motor to.
 
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