Recoil escapement – very variable time keeping

[Andrew CattellParticipant @andrewcattell93655]

I put a temporary pendulum onto a clock with a recoil escapement. The upper half of the pendulum rod, down to just below the crutch, is standard and rigid. Below this point the lower part of the rod and bob unhooks for moving the clock around. My temporary lower pendulum is not a tight fit onto the hook on the upper rod allowing the lower pendulum to swing through a different angle to the upper part. The lower part is actually a key fob with a short length chain and has a trolley token for the bob. In use the clock gains 3 mins a day for the first few days after winding and then evens out for a day and then for the remainder of the run it loses progressively more each day until I wind and reset it. It runs for over 10 days if left to.

When I make a more permanent lower pendulum with a snug fit onto the hook, is it likely that the time keeping will become less variable over the week/10 day between winding? I have two other similar clocks, both keep much better time than this one.

Andrew.

[Andrew CattellParticipant @andrewcattell93655]

Help request

[John HaineParticipant @johnhaine32865]

Assuming that it's spring drive, as the spring unwinds the driving torque reduces. This will reduce the pendulum amplitude.

Depending on just how it's set up the recoil escapement will cause an "escapement deviation" which varies with both amplitude and driving torque It's quite common for the rate therefore to vary as the spring unwinds.

The articulated pendulum will also behave in a slightly unpredictable way which can't help! In fact such structures can swing "chaotically" at higher amplitudes. Ideally you would securely fix the pendulum rods together so it becomes rigid and behaves as one pendulum. With luck it will then keep better time but is hard to predict as there could be other problems.

[Adrian DownesParticipant @adriandownes83818]

What you have at the moment is NOT a simple pendulym so different rules/laws apply & you cannot directly apply your observations.

When you make a more sensible & secure pendulum then, assuming that the rest of the movement is in good order, you can expect a slight variation in timekeeping – gaining a little at the start of the week & losing it at the end.

[Martin KyteParticipant @martinkyte99762]

I think you are seeing the expected error in rate comensurate with the variation in torque over the spring wind as has been said already. However 3 mins on the first day is excessive and so I think the pendulum design is not helping matters. What I think is going on is the 'compound pendulum' is more sensitive to amplitude than a simple pendulum with a rigid rod especially at high amplitudes. No idea how to model it.

Better attention to winding control will help. Clock springs are much more constant when operated in the 'middle' part of the winding so choosing a spring with extra length and limiting the wind to eliminate the full wound and fully unwound state helps enormously. This is why most fuzee clock have stopwork. you could do it manually bu counting turns.

regards Martin

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