This is a motor drive for a desk clock that I want to design. AC synchronous motors are really cheap, but they can rotate in either direction. This mechanism always rotates in one direction regardless of the direction of the input.
This mechanism is designed to fit on a TYC-50 AC synchronous motor similar to https://www.amazon.com/CHANCS-TYC-50-Synchronous-5-6RPM-Torque/dp/B013W3UAE2
TYC-50 appears to refer to the 50mm body size. Apparently, they are used to drive microwave oven turntables. Notice how the food sometimes rotates in random directions. The power dissipation is 4W, so it gets quite warm. I plan on running it with an AC wall transformer at 6-8V. It should drop the power down to around 1-1.5W which should still be plenty of power to run a small clock.
Print all_files.stl or select the files individually (printing two copies of middle_plate.stl and output_gear.stl).
The axles are short segments of 3mm rod. The design needs three pieces 0.69" long and one piece 0.46" long. One of the 0.69" pieces is used as a horizontal pin for the drive gear.
The motor attaches to the back plate with two #4x1/2" wood screws. The drive gear and middle gear get sandwiched between the two middle plates with a 0.46" axle. The structure should easily swing from side to side. Add the output gears with the 0.69" axles and secure the top plate with two #4x1/2" wood screws.
The output should rotate in a constant direction at the same speed as the motor. My motor runs at 6RPM in the US or 5RPM if you have 50 Hz AC power.
11-Apr-19 update: I added a cover box that is just large enough to hold a couple of small wire nuts to the power connections. It should also fit a 3W series resistor if you need to reduce voltage slightly. It is on the third day of a long term reliability test right now and is making a small amount of noise that wasn't there on the first day. Let's see how long the motor lasts.
22-Oct-19 update: The motor has been running on and off for several months now and is still spinning. I started designing a desk clock using this motor and had a really tough time figuring out the motor speed. It turns out that the motor is only approximately 6RPM. I opened one up to see what is inside. There is a permanent magnet in the center followed by 5 gear sets. The first gear set has 12 teeth driving 69 teeth. The next gear set has 21 teeth driving 43 teeth. I counted several times to be sure. They are using prime gear ratios to allow more uniform tooth wear patterns. This may be great for driving a microwave oven where longevity is more important than an exact speed. However, it looks like it may be extremely difficult to generate the exact gear ratios needed to drive a clock. Also, I tested a different brand motor and got a slightly different speed. One was 5.824RPM and the other was 6.228RPM. It looks like I need to find a more consistent motor before going through the effort of designing a clock around it.