Monday, February 18, 2019

"Hidden" power losses in Woodward's escapement

I have been thinking about how my implementation of Woodward's intermittent grasshopper is not successfully transferring enough power to run.  The pendulum power requirements I computed earlier are certainly sobering -- even though this clock's pendulum already appears to be substantially more efficient than my other clocks -- they are not the only power loss. 

Since the escapement runs intermittently, I can dramatically increase the power supplied by the escapement by repeatedly triggering the escapement.   In one experiment I tried, the triggering mechanism got jammed, which triggered an impulse every swing.  This was enough to run the mechanism until the pin escape wheel got stuck. 

But even when triggered every swing, the power supplied is only marginally sufficient, even setting aside the pendulum losses.  If I look at the amplitude immediately before and after an impulse, it's not noticeably different.  This indicates that there are substantial additional losses that occur during the triggering and impulse.

What can cause this? The most obvious (though probably not the only) energy losses are caused by the fact that it takes a definite amount of energy (force times distance) from the pendulum to move both the triggering lever and impulse hook.  Since both of these fall back to their original positions after the impulse without returning this energy to the pendulum, all of this energy is lost!  So, the return counterweights should be heavy enough to ensure a reliable positive action, but otherwise as light as possible. 

(I recall now a similar issue with Clock 3, where my initial attempt at a sprung detent resulted in too much energy loss.  Since I couldn't get the wooden spring weak enough without breaking it, I ended up opting for a light counterweight.  It's probably still too heavy, and may account for much of the need for a heavy drive weight.)