Stirling engines - Adjustable Stirling engine crankshaft

I've been busy making the tips of my fingers raw.

Wire seems to enjoy hurting people.

But I love the stuff.

My time learning how to make screw in eyelets for my hand made fishing lures was well spent. Every new skill I pick up seems to inform my next project. Working with wire is a really worthwhile thing to learn.

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One thing I don't really understand is the relationship between the size of the cams on the crankshaft and the performance of my little tin can Stirling engines. With this lack in mind, I thought I'd build a completely adjustable crank shaft.

It looks like this.

With it, it should be easy to try a stack of different configurations to see what they do.

The cams (bits that are offset from the main shaft) should offer different combinations of engine torque, and speed when they are adjusted to different heights.

I think.

Ideally I need an adjustable chamber for the displacer as well. I'll have to feed that idea through the invention engine at some stage because I have no idea on that one.

All the brass fittings come from the brass bits in strip electrical connectors.

Once the screws are undone as far as they can go, all the brass bits fall out with tap and a jiggle.

Lots of taps and jiggles actually, but they all come out in the end.

In my adjustable cam, the brass tubes that accommodate the cams have had an extra hole drilled through. Brass is very easy to drill, and a pleasure to work with. I don't think I've ever done anything with brass before.

I officially like brass.

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Also, many other people have used these as the adjustable bits on Stirling engines, and my only contribution to the science is to take their use to absurd levels.

120 Things in 20 years - No time to post because I'm too busy learning stuff about Stirling engines.

All the brass bits are taken from a strip of electrical connectors.


  1. The length of the cam offset should be half of the 'stroke' the displacer takes. This way it can reach top to bottom in one stroke. The cam with a half-stroke offset does the whole 50% above and 50% below the centerline.

    The longer the stroke, the more power (torque) and slower running the engine goes. The shorter the stroke, the less power and faster it goes.

    For really fast movement, you want really small parts as they have less mass and the engine won't try to chase you across the room with all it's rattling around a heavy displacer would create.

  2. I'll use the adjustable crank to set the limits and then create a proper one based on the result of the adjustments.

    Getting a bent wire crank just right is actually quite tricky. Even if all I had was the brass mounts to allow me to remove the crankshaft to bend the wire. it would be worth while. It's very difficult to make adjustments when the shaft is in place, and once the shaft gets out of true, it never runs quite as well.

    Trying to bend the wire based on measurements as you build the thing doesnt really allow for getting the displacer as close to the top and bottom as you can.

    No doubt everyone who isn't me will have a better standard of production, and might actually be able to use a ruler :)

    Also the adjustable cam will allow me to gradually wear the hole in the top of the displacer in some controlled way. Once you turn over the engine with the crank adjusted to too big (almost inevitable when you are trying to bend the wire in situ, the hole for the displacer wire will always be just a tiny bit bigger than it should be.

    Even if the entire adjustable thing is going too far, I really recommend using a removable mount for the cam shaft so you can pull it off to adjust it, or replace it.

    Making the shaft supports from wire also allows a stronger material for the bearing surfaces than holes in the tin can. I use a spool of stainless steel welding wire to make the eyelets. Very smooth and very hard.

    Counter weight on the flywheel, and a stable base should go some way toward keeping the thing from shaking itself to bits :)


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