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Author Topic: Gnomish Clockwork.  (Read 3752 times)
BigFuzzy
Swab

United States United States


« on: October 05, 2010, 01:38:55 am »

I'm not a steampunker like you guys, though I do find the stuff fascinating; instead i'm much more interested in working with clockwork. I'm a medieval Re-enactor, and I've come up with a solution to a dilemma I had...only to have a new set of dilemmas.

I love spit-roasted meat, theres just something about a big slab of animal slow roasted over coals by spinning slowly. Sadly, standing there turning a spit for hours on end just isn't fun. So for some time i've been considering buying an self-turning spit; sadly this is not period to the medieval/fantasy mind-frame. So, i've decided to go gnomish with it and use gears and springs.

Basically, it would be a pendulum clock: pendulum weight, mainspring barrel, escapement. Instead of turning hands though, it's going to turn everything from small chickens to twenty pound beef roasts. Hell, a whole pig if that's possible..that would be so awesome. Anyways, i'm sure the readers who have worked with this clockwork will immediately see my problem. I'm going to need some huge piece of mainspring to turn something like that. Not to mention building an escapement that will be able handle that much torque and keep it controlled.

So my question to you, oh anachronistic ones, is where can I find such a spring? Is it even possible to find something as large as i'll need? If not....how can I make one?
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pewtersmith
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« Reply #1 on: October 05, 2010, 02:33:43 am »

You don't necessarily need a clock spring , just a weight , cord ,escapement , pendulum and just enough gearing to get the RPM you desire. A weight driven work would also be truer to the time period ,  and if you wanted to be authentic you should use a verge(or crown wheel) escapement since the pendulum didn't come into use until the renaissance .
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Narsil
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« Reply #2 on: October 05, 2010, 07:09:55 pm »

Yeah a spring isn't really ideal for that application. In clocks and watches the spring is only putting small amounts of energy into a finely balanced system... basically a clock is a reasonable attempt at a perpetual motion machine and the spring makes up the shortfall, compensating for the small frictional losses.  

Spring power also has the inherent problem that the force exerted by a spring is proportional to its displacement, so the force supplied drops off as the spring unwinds. It is possible to devise mechanisms to equalise this but they are quite complex.

If you actually want to do a significant amount of mechanical work springs become a lot less attractive, they're good at dealing with large forces over short distances but as energy stores for moderate work over long periods they aren't so great.

I think that Pewtersmith has got it bang on, a falling weight would suit your purpose a lot better. A spring wouldn't be impossible but using a weight is an all round more elegant solution to this problem.

It would also be a useful addition to include a mechanism to rotationally  balance the spit so that it requires a constant torque to rotate ie the meat on the spit isn't acting as a pendulum, this would reduce the overall amount of energy needed adn keep the turning speed more constant. A simple sliding weight on a crank should do the trick.
« Last Edit: October 05, 2010, 07:13:58 pm by Narsil » Logged







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BigFuzzy
Swab

United States United States


« Reply #3 on: October 06, 2010, 12:05:52 am »

Much obliged gentlemen. I spent the majority of work today working this out in my head, and you're right, it is a much simpler and more elegant solution. ALso, from the outside, it'll look a lot cooler; we all know that's half of the battle.
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Rao
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TheGeekFather
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« Reply #4 on: October 07, 2010, 05:08:54 am »

The easiest way I see to do this is to Add an Anchor escapement to one side of the spit and a weighted rope wrapped around the other end. But instead of just having the weight dangle down thread the rope up to a pulley set up high and run the rope through it and then add the weight.

Here is a quick and dirty design I just threw together.

Spoiler (click to show/hide)

Of course not to scale by any means. I would suggest a wooden gear and anchor untill the design is proven. Yes you can put it all on one side. I just did it this way for demonstration purposes. Having it on both sides would take up alot more space. And need a little more support structure.
The pendulum would need to be an adjustable weight with a set screw.

You would not have to utilize the actual spit but if you made the spool to hold the rope with an extension that could clamp onto the spit it would make it simpler.

I find visual aids a big help. If this isn't what you are working for write up a summary And I'll try to throw another visual aid together. But I do prefer the simpler approach to things. Unless of course you WANT to make it more complicated. Like adding an arm that auto bastes the roast. Hmmmm actually that wouldn't be THAT hard.

EDIT:
Was board so went a head and threw together what I think could work. might need more suport not sure.

Spoiler (click to show/hide)

The little gray piece on the left side of the spool is a spring or some other type of mechanisim that keeps the spool up against the gearing. You will have to wind the rope back up so You will need a way to free spool.

I really don't think a single support spike would work. Be to flimsy. But you should be able to build off this fairly easily. I did sandwich the gear between the spool edge and another plate to keep the anchor in line. I would not Use the spit as the main pivot, but instead have a sleeve that could lock onto the spit. That way the spool, gear  and rope could all be one unit.
« Last Edit: October 07, 2010, 07:38:43 am by Rao » Logged

Raolin Aeromancer

Tinkerer
HR
Zeppelin Captain
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If at first you dont succeed, hit it with a hammer


« Reply #5 on: October 28, 2010, 04:25:56 pm »

small dog and a treadmill, thats how the victorians did it Grin
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tophatdan
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« Reply #6 on: October 28, 2010, 09:03:20 pm »

small dog and a treadmill, thats how the victorians did it Grin

or a child
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Prof_Von_Grumbleflick
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London & Western Home Counties Steampunk Society


« Reply #7 on: November 14, 2010, 10:34:22 pm »

small dog and a treadmill, thats how the victorians did it Grin

There's a pub at the George Inn, Lacock, Wiltshire. A lovely little pub, but the main feature being an open fireplace and still installed is a Dogwheel, surrounded by pictures of it in use (a jack Russell whose name I forget). Probably not your ideal solution, but still a lovely little curiosity.
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Mercury Wells
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« Reply #8 on: November 15, 2010, 11:05:01 pm »

Turnspit Dog

"Whiskey" The Turnspit Dog
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Prof_Von_Grumbleflick
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London & Western Home Counties Steampunk Society


« Reply #9 on: November 15, 2010, 11:18:42 pm »

Brilliant, Mercury!

I didn't know it was a separete breed though. Looks kind of cute. God knows where I got Jack Russell from then. haha!
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Mercury Wells
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« Reply #10 on: November 15, 2010, 11:29:33 pm »

They did have a go on Victorian Pharamcacy, I think they used a terrier of some sort.
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Prof_Von_Grumbleflick
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London & Western Home Counties Steampunk Society


« Reply #11 on: November 15, 2010, 11:50:15 pm »

a Victorian Pharmacy? Where's that? Sounds interesting!
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Mercury Wells
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I insiste that you do call me WELLS. :)


« Reply #12 on: November 16, 2010, 01:16:14 am »

Victorian Pharmacy
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Prof_Von_Grumbleflick
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London & Western Home Counties Steampunk Society


« Reply #13 on: November 16, 2010, 01:32:17 am »

It actually sounds interesting... Maybe I ought to start watching the telly!
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celephicus
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« Reply #14 on: August 10, 2011, 04:00:11 am »

Think Greek, specifically Hero of Alexandria or Ctesibus, both predating clockwork.

Hero used a heavy weight in a box resting on sand, with a small hole in the bottom of the box allowing the weight to fall at a slow rate. He used this to animate the "Automatic Theatre", a sort of animated tableau reminiscent of Michael Bentine's Potty Time (look it up).

Ctesibus invented the water clock, where a mechanism was actuated by a float in a vessel either emptying or filling slowly with water. Not so much power as Hero's idea.

Both of these are authentically medieval, since I believe that clockwork in Europe was post medieval??
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« Reply #15 on: August 23, 2011, 09:29:28 am »

well you could use something more like the governors in music boxes, I forget the proper name. it's a sort of paddle wheel that uses air resistance to limit the speed. your spit rod would have a gear with a worm screw mated to it. the worm would be driving a shaft hanging down and on the end would be the paddle wheel. it could also fan the fire if needed. the end of the spit shaft would have a drum to wind the rope around and a heavy weight would hang from that. as it unwound, you can from time to time wind it back around the drum to renew the process.
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Dr. Madd
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« Reply #16 on: August 23, 2011, 06:08:39 pm »

Use dogs or small children to turn the meat.
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What do we want? Decapitations!
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