Author Topic: James Watt Sun and Planet Gear Mechanical Movement  (Read 6753 times)

Offline philjoe5

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James Watt Sun and Planet Gear Mechanical Movement
« on: November 24, 2015, 04:03:06 PM »
Since our makerspace opened last month my own shop time has been limited.  But I thought I’d share a project I’ve been picking away at.

Some time ago I read a story about Murdoch’s and Watt’s sun and planet gear arrangement (1781) to avoid paying a royalty to James Pickard who held the rights to the common crank – connecting rod mechanism.  Since it involves gears and is #39 in the book of 507 mechanical movements which I’m working through, why wouldn’t I make it?

https://en.wikipedia.org/wiki/Sun_and_planet_gear

What I find interesting is that the use of a conventional crankpin – crankshaft mechanism dates back to the 3rd century in the Hieropolis Sawmill so I’m puzzled as to how Pickard could get a patent for this? 

https://en.wikipedia.org/wiki/Hierapolis_sawmill

The first step was picking a steam engine design, then substituting the sun and planet gear for the common crank mechanism. 

I’d built several versions of Ray HasBrouck’s #3 mill engine.  It’s simple, rugged and steams well and I’ve made a good supply of fittings for a 1.25x scale model for steaming at our club meets.



I started this project four months ago and finished the cylinder and most attachments, piston, flywheel with just the valve gear remaining.  The stroke of this engine is 0.860” x 2 = 1.720”.  So I had a gear center-to-center distance of 0.860” to consider.  I have module 1 and module 0.8 gear cutters and I chose the module 0.8 cutters for this project. The closest fit to a 0.860” center-to-center distance is a pair of module 0.8 gears with 27 teeth.

Making the gears was straightforward but since setup is lengthy, I made 5 gears for experiments.  The planet gear is attached to the connecting rod with four brass pins and the sun gear is keyed to the crankshaft.  A brass plate, which I’ll call the orbit bracket, maintains the correct engagement distance between the gears.

Here’s the arrangement of the sun – planet gears.  Flywheel rotation is smooth.



When I finish the valve gear and have it all together I’ll post a video.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline b.lindsey

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #1 on: November 24, 2015, 06:26:37 PM »
Very nice Phil. Can't wait to see the video!!  Glad the Maker space is doing well also!!

Bill

Offline philjoe5

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #2 on: November 26, 2015, 03:37:23 AM »
Thanks Bill.  I really like the sun and planet gear mechanism, it seems to be self correcting as far as alignment goes.  If I loosely connect everything, rotate the flywheel a few times, then gradually tighten everything up, the alignment is good.

The makerspace is going well.  The machining workshop is in week #5, and at week #8 I expect everyone will have completed their Wobbler engine project.  That will have exposed 8 folks to working with metal machining tools who otherwise wouldn't have had the opportunity.  Whether anyone goes on to do more with it is anyone's guess.  But I'm seeing a pretty high level of enthusiasm right now.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline Alan Haisley

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #3 on: November 27, 2015, 02:50:41 AM »
Some time ago I read a story about Murdoch’s and Watt’s sun and planet gear arrangement (1781) to avoid paying a royalty to James Pickard who held the rights to the common crank – connecting rod mechanism.  Since it involves gears and is #39 in the book of 507 mechanical movements which I’m working through, why wouldn’t I make it?

What I find interesting is that the use of a conventional crankpin – crankshaft mechanism dates back to the 3rd century in the Hieropolis Sawmill so I’m puzzled as to how Pickard could get a patent for this? 
Obviously the British of that time didn't have access to Wikipedia  :ROFL:
Alan

Offline philjoe5

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #4 on: December 08, 2015, 03:30:59 AM »
An interesting problem is encountered.  One cycle of the planet gear (con rod) equals two cycles of the sun gear (crankshaft) when gears of the same size are used.  I have my eccentric fastened to the crankshaft.  Therefore, when conventional oscillating rotary valve motion is used, the cylinder gets a shot of steam in port #1 just after TDC and again in port #1 just after BDC which is not good.

I guess the straightforward fix is to put a 1:2 gear setup off the crankshaft to a jackshaft with the eccentric fixed to it.  Then the valve will work OK.

Has anyone seen Watts engine with the planet and sun gear arrangement in The Whitbread Engine at the Powerhouse Museum in Sydney, Australia?  I would like to know how Mr. Watt dealt with this issue.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline John Hill

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #5 on: December 08, 2015, 04:11:51 AM »
Phil, I dont think the crankshaft played any part in the porting of the Watt engine as all port action was controlled by the movement of the overhead beam so the crankshaft could have rotated at any convenient speed,  I think.

Offline Ian S C

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #6 on: December 08, 2015, 10:24:24 AM »
One advantage of the sun and planet gear is that, with the same size gears the shaft moves a x2 the engine speed, there fore a smaller flywheel can be used, quite an advantage in the days of low revs and big flywheels, specially in cost (wasn't Watt one of the first millionaires)

Offline MMan

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #7 on: December 08, 2015, 01:01:21 PM »
And twice as fast means 4 times as much energy stored, if I remember correctly.

Mman.

Offline Alan Haisley

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #8 on: December 08, 2015, 01:19:03 PM »
An interesting problem is encountered.  One cycle of the planet gear (con rod) equals two cycles of the sun gear (crankshaft) when gears of the same size are used.  I have my eccentric fastened to the crankshaft.  Therefore, when conventional oscillating rotary valve motion is used, the cylinder gets a shot of steam in port #1 just after TDC and again in port #1 just after BDC which is not good.

I guess the straightforward fix is to put a 1:2 gear setup off the crankshaft to a jackshaft with the eccentric fixed to it.  Then the valve will work OK.

Has anyone seen Watts engine with the planet and sun gear arrangement in The Whitbread Engine at the Powerhouse Museum in Sydney, Australia?  I would like to know how Mr. Watt dealt with this issue.

Cheers,
Phil
Hmm, the horizontal presents problems compared to a beam engine.
You could put a slider on the conrod with fixed stops left and right. With that arrangement each time you were near LDC or RDC the slider would move. Then its just a matter of building the linkage from the slider to the valve to get things to happen in the right order. You could just reverse the piping from the valve box to the cylinder. I'm pretty sure that I saw a linkage like this but can't remember where - it's certainly not original with me.
A bunch of fiddling for sure, but less than making two more gears and all the fixtures to hold and use them.
Alan

Offline philjoe5

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #9 on: December 09, 2015, 12:19:42 AM »
Thanks for the ideas and information guys.  I need to ponder this a bit.  The sun-planet gear is too cool to discard so I'll come up with some kind of fix, plus I have all winter to play with it

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline philjoe5

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #10 on: December 20, 2015, 11:47:18 PM »
Well officially winter hasn't started but I think I'm nearly good to go.  When I first learned how to make spur gears a few years ago I made quite a few 30T - 60T gear pairs that were just OK, but I kept going until I got some that were better.  So, digging around I found a pair that would work here to get my valve action compatible with my engine cycle.  So I made a countershaft and bracket, moved the flywheel out of the way and I think this contraption should run OK.  Here it is in a pretty rough form.  I just need to shorten the valve operating rod a bit and make a new air inlet.



Video forthcoming

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline Ian S C

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #11 on: December 21, 2015, 12:54:14 PM »
I think I know the type of hot air engine that could easily be adapted to use the sun and planet gear.  A Ringbom engine is the one, only the power piston has a crank, the displacer is independent.  Might be worth a try. :thinking:

Offline philjoe5

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Re: James Watt Sun and Planet Gear Mechanical Movement
« Reply #12 on: December 22, 2015, 11:28:03 PM »
I managed to get the sun and planet gear arrangement in my steam engine working.   :pinkelephant:  The countershaft approach was the simplest solution to the problem of 2 valve cycles per 1 piston cycle for me since I had a few sets of 1:2 gear pairs.  But man, this engine is noisy, and there’s plenty of drag running all those gears.  Some of that is because I’m using gears for the valve cycle reduction that were not the best I ever made.  But, I love it.  It’s a real contraption, almost Rube Goldbergish.  I’m pretty sure this is a one-off, ha, ha. :ROFL:

Videos:

<a href="https://www.youtube.com/watch?v=IoP9lA-PzGg" target="_blank">http://www.youtube.com/watch?v=IoP9lA-PzGg</a>

<a href="https://www.youtube.com/watch?v=PtlGZVUelyw" target="_blank">http://www.youtube.com/watch?v=PtlGZVUelyw</a>

A few pictures



I’ll bring it to Cabin Fever next month and will try to make it a bit more spiffy by then.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

 

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