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I have a picture with various day and night scenes that I would like to hang on a wall and have automatically and uniformly rotated once every 24 hours. The picture is roughly 55cm in diameter, 2cm deep and weighs ~800g. Accuracy is not critical, 1 second in 24 hours would be good, but even 1 minute in 24 hours would be acceptable.

I can get a 24 hour clock movement and even a "high torque" clock movement, but even that only allows for hands weighing up to 20g. Although the painting is circular and fairly uniform I am concerned that it's weight will be too much for the clock movement and it either won't move or will be hopelessly inaccurate.

I can probably arrange the fitting of the mechanism to the frame, but I'm not sure about building anything mechanically complex. Any ideas as to how I can do this?

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Someone asked for something similar before and one difficult requirement which they listed that you did not, but I am almost certain you have, is noise. That rules out small, heavily geared motors.

Gearboxes are mechanically complex if you try to build anything like that yourself, but one approach is to rigidly mount a very large diameter, high tooth count gear to the back of your painting and then mount that gear to the wall through a bearing to the wall. This way, the painting and the gear spin together. Since it's slow and low load, maybe you could get it laser cut from some thicker plywood or plastic to keep the weight and cost down.

This large gear is driven from the outside rim by a tiny motor and pinion. The tiny motor will need to be anchored relative to the wall. I recommend mounting it a long plate that extends from the center of the picture and gear.

Similarly, you can mount support idlers along the bottom rim of the large gear to improve support if you feel like the center-support of the bearing is insufficient but this will increase friction.

This arrangement reduces the number of gear stages required which helps with noise and simplicity and also takes the load off the motor shaft which might cause a weak motor to bind up.

This small motor can be direct drive or slightly geared, depending on what you can find.

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Companies such as Crouzet make small synchronous motors with gearboxes. I would consider,

  • Putting a small gear wheel onto the gearbox shaft.
  • Getting someone with a laser cutter to create an acrylic ring gear with internal teeth to mount on the back of the artwork with some short stand-offs.
  • Hang the ring gear on the gearbox cog wheel.
  • Arrange some hook / retainers to hook in behind the ring gear to prevent the art falling off.

I'll leave the gear and motor speed calculations to you.

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