Sunday, August 27, 2017

Clock 3 torsion pendulum Q

So the pivots on Clock #3 clearly are consuming energy... I tried the torsion pendulum outside the frame (basically just excluding the pivot).  I counted 70 periods before the amplitude halved... which yields a Q of roughly 315.  But there is considerable wobble since the balance itself is badly out of poise.  I tried to clean this up a bit on the lathe and redrill the center hole (which is misaligned).  Repositioning the suspension hanger also helped, so now the rod spins vertically without much wobble except when the impulse is given.

This seemed to help a bit, as the necessary drive torque has dropped to 1.75 inch-pounds, or about 0.34 mW.  This is about 2/3 as much power as Clock #1 uses, which gives basically one day of runtime with about the biggest weight I'm comfortable with.

Much better, but I suspect that there is still easily fixable power loss due to the wobble at impulse.  If the pendulum weight is placed lower (on a longer rod), this should be reduced, and might help matters further.

Wooden clock power consumption

For reference...

Clock #1 is powered by a 10 lb drive weight that falls 46" in 27 hours.
Power = (10 lb * 4.448222 N/lb)*(46 in*0.0254 m/in)/(27 h * 3600 s/h) = 0.5 mW

Clock #2 is powered by a 1 lb 4 oz weight that falls 11.5" in 5.5 minutes.
Power = (1.25 lb * 4.448222 N/lb)*(11.5 in*0.0254 m/in)/(5.5 min * 60 s/min) = 5 mW

Clock #3 (as it currently stands) is powered by a 4.125 inch-pound torque on the center wheel.
Power = (4.125 lb*4.448222 N/lb)*(6.28319 in/rotation * 0.0254 m/in)/3600 s/rotation = 0.8 mW

This explains why Clock #3 power consumption seems high... Torsion balances are supposed to be much more efficient (if lower Q) than pendulums, but this one is not!

Saturday, August 26, 2017

Clock #3 at least runs!

Clock #3 has been plagued by various problems, mostly with the resonator/balance not being really suitable.  One of the things that was exacerbating matters was the passing spring on the detent was still (even after modifications) too stiff.  I went back to various books and found that the passing spring tended to be quite long, passing beyond the locking pallet.  So I modified the spring in that way.  Now it's much lighter.

I thought long and hard about the balance issues, and came to the conclusion that I probably had to face a right angle turn and a torsion balance.  You can see the new right-angle transmission wheel above on the impulse roller assembly.  The other half mounts to the balance through a spring, which consists of a spring, a rod, pin, wheel, and balance (at the bottom of the rod).  Here are the pieces...

... and here it is assembled.

The balance hangs in front of the lower section of the clock frame.  The rod passes through a pivot, which is formed from a steel wire.

This is perhaps not the best option, but it has the merit of making it easy to adjust the depth of the right-angle transmission.  The transmission runs fairly smoothly and noiselessly.

To first approximation, the new balance appears to have a resonant Q of around 12, whether loaded or not.  (Eyeballing 3 periods before the balance amplitude halves, then multiply by 4 according the rule of thumb suggested by Woodward.)  So the pivot and transmission is the least of my concerns, but the fact that the unloaded Q is low is definitely an issue.

The mechanism appears to run semi-reliably...

but it needs considerably more torque than I'd like.  The center wheel needs about 4.125 inch-pounds in order to maintain balance amplitude.  This is concerning because I was really hoping this to be the torque on the drive wheel -- a factor of 10 weaker!  The resonator having so much absolute loss of power is clearly a problem.

Lower on the priority list is the fact that with this balance the clock runs a bit fast.   It makes 17 "loud" ticks per minute rather than 15.  That should be easily corrected.

Thursday, August 17, 2017

Clock 1 humidity redux

I think I have finally figured out what goes wrong with Clock 1 when the humidity changes.  After much watching and poking, I found that the third wheel appeared to be sticking slightly, at least whenever the clock stopped.  Carefully pulling the third wheel backwards once the clock stopped, I could feel some rubbing...

I think the third wheel pinion expanded a bit beyond where it was supposed to, or maybe the frame expanded, but in any event, it was fouling at the tip.  After ensuring that the pivot was rigidly planted where it was supposed to be, I took to very slightly filing the addenda of the pinion.

This makes the pinions closer to an ogive form.  I don't think this really matters, because the clock is now happily running even though the humidity has been around 60%.  Hopefully I won't run into an "opposite" problem when the humidity drops later in the year.