Gallery, Projects and General > Project Logs
The Return of No. 83, a Hot Air Engine
vtsteam:
Replaced ball bearings and crankshaft, and sealed the leak. I also found when replacing the bearings that the hub of the flywheel was contacting the bearing hub -- there was a high spot where a set screw had been tapped into the flywheel hub. Threading had slightly expanded the steel in the area, which was impossible to see, but I could faintly hear a contact sound when the new bearings and shaft were in place and I spun the flywheel by hand close to my ear. I think that was the sound I heard before when run at full speed, thinking it was bearing noise.
I put some marker on the flywheel hub, spun it some more. Taking it apart again, I was able to see the high spot where it had removed the marker. I filed the raised bit down with a small triangular file, and the noise. was gone.
sorveltaja:
--- Quote from: vtsteam on March 14, 2025, 10:19:42 PM ---Hey sorveltaja! :wave: :beer: Great to hear from you! How is your guitar? That was such an interesting project! :coffee:
--- End quote ---
Yeah, that guitar is ok, except its tremolo turned out to have a flaw. Tension of the strings has caused string retainer to rotate(something I didn't expect), and therefore it isn't possible to tune it properly.
vtsteam:
That's too bad, sorveltaja, but I bet, knowing your capabilities that you can change that, if you want to. I remember all of the amazing changes you made. Plus I was really impressed with the rust finish -- I know that sounds funny, considering all of the mechanics, but I thought that was really cool!
re. No. 83, I started on a fourth displacer cylinder today.
It features a thinner steel flange, compared to the last version's thick aluminum, and a reversion to a stainless steel end cap instead of a copper one. I wanted to try go back to the performance of my second cylinder, if possible, by removing some of the added variables.
So far, I've made 4 displacer cylinders, lined up here to show the differences. The first was just stainless steel tubing. Top RPM was around 800. The second had a thinned down wall thickness, and average speed was around 1400 RPM it did hit 1600 rpm on one run. The third cylinder had a changed mounting method. Instead of passing through the aluminum heat sink, it had a flange and mounted outside of it. It ran about 1300 RPM. An improvement in bearings and a sealed leak and removal of a frictional interference produced a max speed of 1440 RPM.
The 4th is a reversion to the second cylinder but with a flange mount.
vtsteam:
Progress had stopped for the last 4 days as I waited while my electrical heating coil project dried out. This coil will allow me to get consistent heat input for testing changes made to No. 83. Sterno does not provide consistent heat as the can contents burn down.
I'm really happy to say the new mini electrical heating furnace works really well with the engine. And with less power than I thought it might take.
The engine starts and reaches a steady state at about 960 RPM at 80 watts @ 10.8V. That was on the porch outside my house at an initial test at a 53 degree (F) air temperature, and some fairly strong breezes.
I think it would probably run faster indoors, but I had to do this initial test outdoors to burn off the fumes from a small amount of tape and release agent used in originally making the coil.
Here's the engine running in a test:
vtsteam:
I don't really have a good data baseline yet for a few reasons, but definitely will be able to do so with the electrical heater. I want to do tests indoors, and I did notice the RPM kept increasing slowly over time, as the wattage actually decreased -- both probably due to the last bit of moisture gradually drying out of the heater, the low temperature outdoors and wind, and the plaster mass heating up slowly.
Nevertheless, I did achieve 1050 RPM at about 100 watts and that speed was increasing slowly, but by then I needed to stop and bring everything inside, because it started to rain.
I'm very, very happy that this heater worked out first try with the amount of wire and power estimated. It was a long wait while it dried. I can now really compare modifications in the engine.
The engine is running fairly loud lately -- I think it's worn big end bearings knocking now. I've got definite plans for improvement!
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