Author Topic: Congreve mechanism  (Read 8379 times)

Offline chuckknight

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Congreve mechanism
« on: February 02, 2009, 08:31:25 AM »
I saw, on Rabbit's page, an absolutely beautiful congreve clock that I would love to re-interpret.  (eventually)  But, of course, I have to know how it works, first.  And, yes, I know that they are notoriously lousy timekeepers.

But, they're just *SO* COOL!


Does anyone have drawings/sketches/diagrams for the escapement layout?  The remainder is just another gear train, and they're relatively straightforward...but the escapement on that thing must be quite different than usual.

Thanks!

Chuck

Offline rabbit

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Re: Congreve mechanism
« Reply #1 on: February 04, 2009, 01:24:54 PM »
Thanks for the compliments! This was one of the first 'original' clocks i made many years ago, and when i look back on it, i can't believe i did that!
The "escape" mechanism isn't conventional at all, but it is pretty simple...

Mine (and the original Congreve, i think) has a 30-second period, and the 'escape wheel' turns once a minute, so it only has two 'teeth'. (The clockwork moves in half-minute increments.) The 'teeth' are more or less just a 'lock' to the wheel. Unlike a conventional escape, it doesn't impart energy to the "pendulum" by way of the teeth and pallet, but rather by the "crank" (part of the 'escape wheel') and push/pull rod attached to the tilting track. This 'lock' is 'unlatched' when the ball - or 'plinth' in mine - hits the 'trip wire' at the end of the track. The 'trip wire' is simply a part of a goofy lever and linkage system that does the unlatching. They are weight-biased to return after the plinth reverses, which returns the lock to hold the escape wheel on the next tooth.
In the photo you posted, the escape wheel, crank, push/pull rod and one of  the 'teeth' are seen in the left. The trip wire(s) are the paired brass rods pointing up through the ends of the tilt track.

My scanner isn't working, and my sketches aren't very informative anyway, but i hope this description helps.
And, yes, it is a poor timekeeper... but a really cool mechanism.
- rabbit

Offline chuckknight

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Re: Congreve mechanism
« Reply #2 on: February 04, 2009, 05:24:31 PM »
The Station Clock is simply lovely...one of the prettiest wooden clocks I've ever seen.  Interesting, different, and beautifully designed.  Frankly, your Time Warp is a masterpiece, but a bit "weird" for most tastes.  Non-round gears must be interesting to make, though.  And, then that Congreve...it is simply something special...simple, elegant, and yet sufficiently different that it retains my interest without appearing weird.  Difficult to accomplish.  You deserve the compliment...

Now, about the Congreve mechanism.  Your description does help...a little...thank you.  But, a rough drawing would be welcome, too.

Bottom line...I'm going to have to think on it a while, to figure out exactly how it works.  Being a visual person, I have to construct and then "animate" it in my mind, before it will make sense...and I'm trying to animate only the escapement/plinth right now.  I understand that it has a 30 second period (how was the period determined, anyway...experimentally?), and thus 2 teeth...but I'm trying to figure out *all* the linkages involved in each cycle.  The hint about the trip levers being weighted (and auto-reset) does help.

A simple cam mechanism could raise/lower each side...but are you saying that the spring provides all the power, and the "pendulum-plinth" does not need to be impulsed like in a regular escapement?  If true, that is the part I didn't understand.

It's obvious that the Devil will be in the details, on this clock...but it's so darned pretty that I just have to make one.

Geez...I think I have 5 clocks in the works, and havent' even started on my first, yet!  And, it's becoming painfully obvious to me that I am enamored with "weird" escapements.  Flying ball, Lenz disc, Congreve, ring, etc.

     -- Chuck Knight

Offline rabbit

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Re: Congreve mechanism
« Reply #3 on: February 05, 2009, 08:50:35 AM »
Thanks, again.
You can see by my collection i have an affinity for the "weird" as well.

The "impulse to the pendulum" is the tilting of the track. This is done by the crank (on the 'escape wheel') and the rod (attached to the track). when the wheel turns - 1/2 rotation per cycle - it pushes the track up on one cycle, and pulls it down on the next. The track itself is balanced, so the energy imparted amounts to "lifting" the plinth. This energy is not insignificant - think of it as 30 regular pendulum impulses at once. Congreve erroneously thought that since the clockworks are stationary for 58 out of 60 seconds, it takes far less power to run. There is no such thing as a "free lunch".

It took some experimentation and prototyping to get the initial period "as slow as i could make it", aiming for 30-seconds. The plinth has tiny pointed axles. The taper makes it self-center as it rolls. And it rolls on the very point of the axles - the tiny diameter means many, many revolutions to roll to the other end.
The push/pull rod is adjustable in length, which varies the inclination angle of the track, and thereby regulates the clock (the plinth rolls faster at a steeper angle).

The pivots of the trip wires lift a long lever, that in turn lifts a small tang that blocks/releases the teeth on the wheel.

Clear as mud?
- rabbit

Offline chuckknight

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Re: Congreve mechanism
« Reply #4 on: February 05, 2009, 09:58:39 PM »
That does help, actually.  Can't wait to finally figure out the subtler points of the basic mechanism.  That way I can prototype it!

THANKS!

Chuck