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Author Topic: Anyone made wood gear clock with electric clock motor?  (Read 1530 times)
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steve323
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« Reply #15 on: October 23, 2019, 12:39:31 PM »

Tmasters, not sure if you are still intereste d, but here is some info that I have discovere d.

I have been running some of the cheap microwave synchrono us motors for several months.  They are rated at 4W and get quite warm.  They still produce plenty of torque at half the rated voltage, so that is how I have been testing them.  The 12V motors are running with a 6V wall wart transform er and the 120V motors use a series resistor to cut the current in half.

These motors will randomly start in either direction, so I built a small mechanism to fix this.  The design is at https://www.thingiverse.com/thing:3548759

Trouble started when measuring the exact rotationa l speed to build a clock.  The motors are rated 5/6RPM, which should be 5RPM at 50Hz and 6RPM at 60Hz.  Both motors are close, but not exactly 6RPM.  One was around 5.824RPM and the other was 6.228RPM.  This may be OK for a microwave turntable, but not for a clock.

I opened one motor to see how they work.  The center hub is a permanent magnet with 4 north poles and 4 south poles.  This should rotate 15 times per second at 60Hz.  There are 5 gear sets with 12:69, 21:43, 16:35, 15:30, and 8:24 teeth.  The 12 and 69 tooth gears are very fine pitch and will likely be the first to fail.  The 21 and 43 tooth gears should wear evenly since they use a prime number of teeth, however they make it difficult to design into a clock. 

The other motor with different speeds must have slightly different gear ratios.  Both should be perfectly stable when running on AC power, but each would need a different gear ratio to drive a clock perfectly .  I think I will look for something else to drive a clock.  eBay has a few Synchron motors in the $20-30 range.

Steve
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