Author Topic: Rhombic drive stirling engine  (Read 479 times)

Offline Roger B

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Rhombic drive stirling engine
« on: February 05, 2021, 08:31:53 PM »
I have decided to have a go at a Stirling engine. As ever it will be my own design and fairly small. As the rhombic drive is new to me I decided to make a test version, maybe some parts can be transferred to the final thing. It starts with an offcut of 12mm thick aluminium strip with two 10mm holes at 30mm separation with Oilite bushes to take two 30 tooth Mod 1 gears.
That seemed to go OK so then I had to mark out the gears for the crankpins. As the gears are the cranks one pin has to be aligned to a tooth and one to a gap. No room for adjustment. Next up is 4 connecting rods.
Best regards

Roger

Offline tvoght

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Re: Rhombic drive stirling engine
« Reply #1 on: February 05, 2021, 08:52:04 PM »
I'll keep an eye on this.   --Tim

Offline Kim

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Re: Rhombic drive stirling engine
« Reply #2 on: February 06, 2021, 05:12:23 AM »
Sounds like a great project, Roger!   :popcorn:

Kim

Offline Bear

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Re: Rhombic drive stirling engine
« Reply #3 on: February 06, 2021, 03:29:00 PM »
I'll be following along. Always wanted to build a Sterling engine.

Offline Roger B

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Re: Rhombic drive stirling engine
« Reply #4 on: February 06, 2021, 03:54:39 PM »
Thank you all  :ThumbsUp: This is, as ever, a learning experience for me. I don't know the level of accuracy required for the various parts. Piston fits obviously have to be good but I am not sure how precise the linkages have to be. Will marked, spotted, drilled and reamed be ok or will jigs and boring be required. I am intending to use miniature ball races in the connecting rods and they will be a transition fit in a h7 reamed hole so some adhesive will probably be required.

The conrods were drilled 3mm and separated with a hacksaw. Next they were milled to the required width, the holes were opened out to 5.8mm and reamed 6mm. Finally the ends were rounded on the RT. The same mark, spot, drill, ream was used on the crossheads which doesn't look too far out.
Best regards

Roger

Offline Dave Otto

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Re: Rhombic drive stirling engine
« Reply #5 on: February 06, 2021, 03:58:25 PM »
Interesting project Roger, I will also be following along.

Dave

Offline Roger B

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Re: Rhombic drive stirling engine
« Reply #6 on: February 07, 2021, 04:21:09 PM »
Thank you Dave  :ThumbsUp:

I milled the recesses in the crossheads but unfortunately hadn't tightened the vice fully  :facepalm: There is a bit of a dig in but the part is okay for the first trials. Next I fixed the bearings into the conrods with some thread locker in the hope I will be able to remove them later (648 is probably a bit extreme). While they were curing I turned the various pivots from 3mm silver steel. Putting it together was a bit tricky as nothing was really held in place but it worked  :)


Best regards

Roger

Offline Kim

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Re: Rhombic drive stirling engine
« Reply #7 on: February 07, 2021, 06:29:35 PM »
That's pretty cute, Roger! Looks like a little man dancing :)

Kim

Offline Roger B

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Re: Rhombic drive stirling engine
« Reply #8 on: February 08, 2021, 03:37:40 PM »
Thank you Kim  :ThumbsUp: It is a rather fun mechanism  :)

The trial version worked well but I will need to make a couple of changes. The working piston crosshead gets rather crowded and if you move the connecting rods outwards to make space for the hollow piston rod the side forces will increase. I plan to have a pair of rods for the working piston with a single rod between them for the displacer piston. I am also not really sure of the forces involved, especially if I want to make this a power producer  ::)
Best regards

Roger