Stirlingengineforum.com

Actually, looking back, the earlier ideas was to have the ring working more on the order of a revolving cam attached to a flywheel.

The Michael engine used a power takeoff that was basically a point on the ring (similar to this video) attached to a crank. (I think many ? There were a few different iterations)

In the above video my hand is off camera but is basically revolving in a circle to create the motion. With the engine running, a crank could be the power takeoff, where my hand is. That might also serve as a fixed point to stabilize the ring better.

On the other hand, after playing with this for a while, I think maybe I had too many pivot points and maybe an "elbow" joint is not necessary. Something like this (I added the crank/power takeoff pulley whatever thing.

I had a thought also, if the engine likes heat nearer to the center of the cylinder (depending on the design) a narrowing of the updraft chimney pipe at the point where the engines are attached might create a kind of vacuum venturi type effect helping to draw cooler air into the chimney through some holes on the pipe helping to keep the engine(s) cooler on the cold power piston side while focusing the heat more where it would be needed.

Tom Booth wrote: ↑Mon Apr 10, 2023 11:24 am I was curious to see how the linkage might work with just an outer ring connecting the pistons together as originally proposed (without any cams or lobes).

I had the idea of a captive ball bearing for this. Basically a ball at the end of the piston shaft rolling in a track on the ring.

Kaoron wrote: ↑Mon Apr 10, 2023 2:22 pm

Tom Booth wrote: ↑Mon Apr 10, 2023 11:24 am I was curious to see how the linkage might work with just an outer ring connecting the pistons together as originally proposed (without any cams or lobes).

I had the idea of a captive ball bearing for this. Basically a ball at the end of the piston shaft rolling in a track on the ring.

Something like this maybe?


The engines driving a kind of off center lazy Susan.

The thing I had taped down to the table was actually out of a kind of lazy Susan snack tray

Maybe have a whole stack of these reverse radial engines all the way up the stove pipe and with the eccentrics staggered for better balance, less vibration, more power.

Tom Booth wrote: ↑Mon Apr 10, 2023 1:08 pm I had a thought also, if the engine likes heat nearer to the center of the cylinder (depending on the design) a narrowing of the updraft chimney pipe at the point where the engines are attached might create a kind of vacuum venturi type effect helping to draw cooler air into the chimney through some holes on the pipe helping to keep the engine(s) cooler on the cold power piston side while focusing the heat more where it would be needed.

That's precisely what I was referring to in the opening post :

the cold source can be arranged to benefit from the stack effect (draft) from the heat source, getting cooled by the renewed air aspired into the chimney

---

Tom Booth wrote: ↑Mon Apr 10, 2023 3:14 pm Something like this maybe?

More like this : ---

Tom Booth wrote: ↑Mon Apr 10, 2023 4:21 pm Maybe have a whole stack of these reverse radial engines all the way up the stove pipe and with the eccentrics staggered for better balance, less vibration, more power.

Stackability is one of the perks I envisioned, if the design proves useful. I like the idea of staggering the eccentrics to balance the system!


Thanks for putting some brain juice into this design, it's nice to have someone to bounce ideas off :)

Kaoron wrote: ↑Mon Apr 10, 2023 7:31 pm

Tom Booth wrote: ↑Mon Apr 10, 2023 3:14 pm Something like this maybe?

More like this : Screenshot 2023-04-10 at 21-15-40 3D design Sizzling Lappi-Stantia Tinkercad.png

That certainly makes more sense. I was wondering how the piston would return. It might, generally on its own but could potentially get stuck on the inward stroke.

I was thinking of putting a spring on the piston rod to keep it pushed out, but your grove design would completely avoid the issue.

Another option would be some sort of magnetic levitation track, but I feel this would steer away from the cheap and low-tech intent I had.

I'm wondering if a relatively large flywheel/track without cam lobs (essentially one big cam with a 1:1 ratio between flywheel rotation and piston) would keep up with the frequency the piston "wants" to run at.

I guess, the synchronization is forced so like it or not, the piston will follow the track, but I'm thinking there could be a disparity between how the piston would "naturally" reciprocate "free piston" if it could and how fast the rather large flywheel could spin.

I guess this is true of any engine with a crankshaft and flywheel and doesn't really present a problem, but relatively speaking, the pistons would likely be unusually small and the flywheel, unusually large with this setup.

If the track cannot spin fast enough, the "slope" of the "cam" might not be steep enough so the piston rod might feel like it is just pushing and pulling against a wall. And so, the Michael engine design with many relatively closer spaced lobes might actually give the pistons more freedom of movement to follow their natural rhythm.

I've been thinking about how it might be possible to get a nearly perfect tracing for cam lobes.

It would depend on the required RPM to turn whatever generator or whatnot but basically:

Build the engine so it can run off the stove pipe or whatever heat source but mounted in such a way that it could be made to revolve. Probably an artificial heat source like a heating element would need to be used to mimic the actual intended heat source.

Anyway, let the engine (just one cylinder would be needed I think) run "free piston" with just a small LED attached or probably just a dot of white paint would do.

Revolve the setup (with the the engine running) at the desired RPM (cam rotation speed) and use a slow shutter speed or open shutter to take a picture from above.

The LED or paint spot should photograph as a trail or tracing

I suppose this could also be done mechanically, like a seismograph tracing using a pen attached to the piston shaft while revolving a disk

Maybe mount one of those model engines over an old phonograph vinyl record turntable.

Maybe some resistance could be applied to simulate various load conditions.

The basic idea is just, get an actual tracing of what the piston motion would look like. Presumably, a cam design that matches that profile would allow the engine to run at, or near to it's "natural" operating frequency.

Maybe the engine could be stationary and the camera could be revolved


https://youtu.be/-x9sjg15TwY

I think you can just take your idea of a seismograph-like pen attached to the piston and write the trace on a ribbon for a temperature t.

Roll the ribbon at a fixed speed s, take any amount of cycles to find the diameter of a circle. An ideal frictionless zero-weight lobed cam wheel will do one revolution at the corresponding speed for that temperature.

(I'm probably wrong about something, whether it's physics or trigonometry, but I think it's a good base to iterate on)

A type of linkage that may not be mechanically deadlocked :