Anyone made wood gear clock with electric clock motor?

[ArtF]

True, Sync motors are the gold standard and a lot less hassle.
 
Art

[Tmasters]

Steve - Wow, that looks like exactly what I want!  Constant RPM but no computer to deal with.  I'll look into that and check to see if it has any interesting relatives.  Thank you!

Tim

[steve323]

Tim,

Your query sparked my interest, so I ordered a couple of motors similar to these https://www.amazon.com/dp/B07G345S4H  Similar items are common on Ebay for around $3 each.

They appear to be very popular for running the turntables in microwave ovens.  The first test runs amazingly quiet with a lot of torque because of the gearing.  I may try to run one for a few weeks with a load to see if it stays quiet.

One huge disadvantage is labeled clearly in the image as CCW/CW.  The motor does not have a start capacitor to define the direction and will randomly start either clockwise or counter-clockwise.  Directional synchronous motors are a lot harder to find.  It should be a fun challenge to use a couple of one-way clutches and gears to force the output to run in one direction.

Steve

[John T]

Just a thought,  If I truly wanted to have exposed wooden gears and an accurate time piece - I would look at running th clock backwards - by that I mean I wouldn't start at the great wheel but rather start at the seconds hand and let everything else follow it.  In a normal geared clock you start with a lot of power (weight) and through gearing slowly have less and less actual power at the gear tips.  If you apply very small power from an electric movement at the seconds hand you could let there rest of the mechanism just follow along.

[Tmasters]

I agree, and that was my eventual plan.  But I'm still hung up on motors.  The many synchronous motors I looked at would be perfect if it were not for the fact that they all have an average rated life that is much too short for a clock that runs continuously.  So now I'm looking at a pendulum movement with a hidden magnet in the base of the pendulum and a hidden electromagnet behind the front panel.  I would use a simple microcontroller to apply tiny tweaking pulses to keep the pendulum on track.

[steve323]

Tmasters, not sure if you are still interested, but here is some info that I have discovered.

I have been running some of the cheap microwave synchronous 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 transformer 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 rotational 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