Hi there @ All About Circuits,
I am looking to purchase an AC motor to turn a sculpture. The sculpture (pictures below) is around 25 lbs including the metal pipe. I was thinking to attach the base of the pipe to flange / wood and somehow affix that to the motor shaft, all house inside a rugged hollow wooden box with a hole for the pipe to rise through. Sculpture would make two full rotations each minute.

I realize this is barely an electronics issue, and mostly mechanical but I'm unsure where else to turn as everyone seems so helpful on these blessed forums. I attached a rough sketch of the mechanical concept . . .

 

saw this, but don't want to drop the investment until I know it's within ballpark of something feasible lol
https://www.amazon.com/Electric-Sin...p/B095WWD746/ref=psdc_306577011_t3_B0B4W3K1HT

 

Welcome to AAC!

That is overkill.
Will the metal bar or pipe stand vertically?
If not, sketch out how the sculpture is to be oriented on the motor.

How about something like this?
https://www.surpluscenter.com/Elect...motors/2-RPM-120-Volt-AC-Gearmotor-5-1913.axd

 

The main problem is the bending torque on the motor shaft.

I suggest designing a bearing support that is very robust, then couple the drive motor with a belt.
The application only needs a small cheap motor, but these have very wimpy output shafts.

 

Welcome to AAC!

That is overkill.
Will the metal bar or pipe stand vertically?
If not, sketch out how the sculpture is to be oriented on the motor.

How about something like this?
https://www.surpluscenter.com/Elect...motors/2-RPM-120-Volt-AC-Gearmotor-5-1913.axd

Oh very cool! To answer your question, arm and pole will be upright. Thanks again for this referral. My next question would be : How do I best secure the motor shaft into the wood which flange + pole is screwed into?

 

The main problem is the bending torque on the motor shaft.

I suggest designing a bearing support that is very robust, then couple the drive motor with a belt.
The application only needs a small cheap motor, but these have very wimpy output shafts.

Sounds like a solution, but way over my head :/ I know I will need to do some work, regardless of what motor I purchase. I just dont know how to make a bearing support or how the belt should be designed aargh

 

The motor in post #2 can attach to a pulley with a 1/2" bore. Go to Amazon,com and search
v-belt pulley 1/2" bore

then measure (accurately) the Outside diameter of your pipe (preferably with a caliper. Also helpful if you know the thread tap size on the end of the pipe (if any).

 

A clutch thrust-bearing (from a car wrecker's yard) would make a good support for the shaft base. A suitable ball-race could support the shaft further up.
A microwave oven turntable motor, with a 10:1 ratio further reduction gearing using a belt-and-pulley arrangement, would probably give enough torque and the right speed for your application.
If the sculpture will be touchable by the public then some sort of slipping drive would be advisable in case some idiot tries forcing the sculpture round.

 

The biggest problem I see is mechanical, but that may be because I am so bad at mechanics.

How do you keep the thing from wobbling on that very long shaft?

If the shaft has any curvature, it will be multiplied by the length and there is no way to fix it.

And you cannot just mount it to the motor shaft because it would have to be perfectly parallel to avoid wobble, and the motor bearings would have to be very strong.

This is why others have proposed two bearings for the shaft, separated by, I would think, at least 6 inches.

 

That looks to me like some kind of 1/2” rod. Does it have to be that?
Can you replace it with 2” black PVC pipe?

 

That looks to me like some kind of 1/2” rod. Does it have to be that?
Can you replace it with 2” black PVC pipe?

PVC would look great as part of the arm sculpture. Your right, Black would class it up. That way, you can see the manufacturers ink-jet printed label along the length of the pipe twice per minute.

 

Hey Everyone! Thank you all so much for the responses. 1) I ordered the motor suggested by Mr Chips here https://www.surpluscenter.com/Elect...motors/2-RPM-120-Volt-AC-Gearmotor-5-1913.axd
2) I can absolutely cut the pipe down to a much smaller length. If the pipe is only a few inches from the arm, screwing into a flange that then attaches with wood + JB weld or some crap to the motor shaft would that prove feasible without the living hell of belts, pullies and the like?

I love this forum, and I use that word sparingly. Downright beautiful people on here....
Best,
-M

PS Kind of badass these are manufactured in Korea

 

That looks to me like some kind of 1/2” rod. Does it have to be that?
Can you replace it with 2” black PVC pipe?

Good question! I do have a coupler for a 1/2" pipe already embedded into the sculpure's elbow. But, I can shorten the length of the pipe to even just a couple of inches if it makes this all easier from a mechanical perspective.

 

I used a very small motor to spin a barbie doll on top of a music box as a prop for a dance routine. I mounted the motor inside a 3D printed cylinder that included batteries for a micro, the motor and lights on the doll’s dress. The shaft of the motor the motor went into a hub that was to attached to a slideable piece of wood fastened to the bottom of the box, adjustable for centering. A shaft came out of the cylinder and fed through a bearing in the top of the box. Worked beautifully.

 

I used a very small motor to spin a barbie doll on top of a music box as a prop for a dance routine. I mounted the motor inside a 3D printed cylinder that included batteries for a micro, the motor and lights on the doll’s dress. The shaft of the motor the motor went into a hub that was to attached to a slideable piece of wood fastened to the bottom of the box, adjustable for centering. A shaft came out of the cylinder and fed through a bearing in the top of the box. Worked beautifully.

Very cool, thank you for sharing. I basically understand everything except for "a shaft came out of the cylinder and fed through a bearing the top of the box." What is a bearing and why did you need it? Cheers...

 

Very cool, thank you for sharing. I basically understand everything except for "a shaft came out of the cylinder and fed through a bearing the top of the box." What is a bearing and why did you need it? Cheers...

A bearing is a cylinder filled with ball bearings and allows your part to spin in a well-lubricated and well-designed system rather than simply eroding the rim of a hole drilled into a box.

 

A bearing is a cylinder filled with ball bearings and allows your part to spin in a well-lubricated and well-designed system rather than simply eroding the rim of a hole drilled into a box.

Okay, got. If you dont mind my line of questioning ; how does the motor shaft connect to the bearing if the bearing is simply a cylinder? And how does one connect the part to be rotated (in my case the arm) to the top of the bearing? I appreciate it. Total noob here...

 

Ah maybe this? XD

 

Ah maybe this?

Not for your project. Do yourself a favor and get 2 flange mount pillow blocks. By mounting them on either side of the top of your base, with the shaft going through them you will get all of the support you will ever need for this. You need to measure your rod and pick the correct size. This link just shows what the pillow blocks look like, you may get a better price on Ebay or Amazon. https://www.surpluscenter.com/Bearings/Cast-Iron-2-Bolt-Flange-Mount-Bearings/

 

I was going to suggest a barbecue rotisserie motor. I can pretty much guarantee there will be couple at Value Village in the tools/autoparts section. The motor you ordered says "intermittent duty"; barbecue motors would be rated for continuous duty.