## Thursday, February 8, 2018

### A Little Machine Shop Steam Engine Puzzle

I've done some experiments with my little "steam" wobbler engine over the course of the last week.  I tried it with three different flywheels.  As always, there's a story behind this, but first, if you're so inclined, here's a four minute video that shows the experiments.

The video is a combination of three separate videos.  The first video is the solid one in that's mounted on the motor in the still photo thumbnail you should be seeing.  That flywheel is actually a remake of the first flywheel, which is the one on the left with the six half-inch holes in it, and I posted when I drilled the holes using my rotary table.  That flywheel was on the engine in the video I posted in that link at the top.  The brass (bronze?) wheel is smaller than the others, 2" diameter instead of 2-1/2".  The weights of the solid aluminum flywheel and that one are within 6 grams of each other, but the important mechanical property is the moment of inertia, and I haven't calculated that.

What's the bottom line?  As of the moment, I like the looks of the lightweighted aluminum best, and the solid aluminum one the least, but the solid aluminum wheel is on the engine for now.  It wobbles more (visible in the first video) and despite that it runs best down to the lowest pressures (12 or 15 PSI).

The engine is "touchy", the tightness of the flywheel is critical.  Right now, there's about .010 gap between the upright and the flywheel and it runs well.  If I adjust that gap so that there's virtually none, the engine won't run.
In this view, it looks like they're solidly against each other, and the same with the crank wheel on the other side.  If they're that close, I can't get it to run.

1. It appears that the looseness in the crankshaft makes the clearance necessary. Closing up the clearance causes the wheels to bind on the central plate, I suspect. This model is a "demonstration of principle" item. What it badly needs is a bearing housing with, at minimum, bronze Oilite bushings separated as widely as practical.
https://www.mcmaster.com/#sae-841-bronze-bushings/=1bhlc62 should do nicely.

1. I was thinking of turning one from delrin, since I still have several inches of rod left. Alternatively, I can get ball bearings with a 1/4" bore (the shaft size) that will sit in a 3/8" hole, recessed a little.

But I tell myself it's really a toy, or "demonstration of principle" as you say, and it's probably doing what it's going to do.

2. But just think of the fun you could have rigging it up to run some "animated" outdoor display for Christmas! And really run it off steam from a pot sitting over a bonfire in your front yard...
}:-]

3. I don't know what kind of power these things can deliver, but I'm sure they could do something. The displacement is about 1-1/2 cubic inches, so not much. Still, that's about 26 cubic centimeters and there are tons of 49cc motorcycles out there that people actually ride.

4. You've got plenty of time to work it up between now and Thanksgiving...

And for extra credit, you could have the boiler cooking mash and condense the "steam" output from the engine into moonshine! Sit there sippin' merrily away whilst the world drives by!
}:-]