Gallery, Projects and General > Project Logs
Making a Prony Brake to Measure the Power of My Hot Air Engines
Country Bubba:
I think there is a good possibility the springs will stabilize and help maintain the brass nut position. Think the spring on a needle jet of a lawnmower engine?
vtsteam:
Yes CB I was thinking that also, presently the pressure needed is so light that the springs have no locking effect.
I've put a tiny dab of silicone rubber sealant on the bottom of the thumb nuts and that seems to be working to increase friction without adding so much that they are hard to turn.
Other changes yesterday: I Tung oiled the brake arm instead of varnishing. Disassembled and cleaned engine (see the No 83 thread).
I tried to set up a digital Hall effect tachometer with a panel meter and transducer received from Ebay, but it seemed defective. It just read 7777 or LLLL when powered up (depending on how you look at it). Today, I tested on a loose flywheel with magnet and figured out this was normal behavior, unlike my other Hall tach on my lathe, which shows 0000 when stationary. I had initiated a return, but cancelled it once I realized it worked. This could have been avoided by including a one line instruction sheet. Oh well, on with the show....
vtsteam:
I made up a digital tach tonight. It all fit in the lid of a plastic box.
Display, bottom. Switch, upper left. Battery, right, held in place with velcro. Hall sensor, top right.
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The case assembled, and the weird LLLL display:
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To trigger the Hall sensor, a very small wafer magnet was attached to the outside rim of Prony brake drum with high strength bearing mount adhesive.
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vtsteam:
And here's a mockup of a test setup. It will need to be mounted on a base so vibration doesn't move the various pieces around. But I couldn't help but give it a test spin this evening.
The accessories made for engine testing are:
1.) A variable DC power supply. Here supplying 100 watts for heating the displacer.
2.) A DIY electric furnace made from Plaster of Paris with stainless steel aircraft safety wire for an element.
3.) DIY Prony brake from steel, brass wood and a digital scale (yes, I still need to shorten and reverse the stylus)
4.) DIY Hall effect digital tachometer.
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BTW this photo was at startup. Engine reached 1200 RPM eventually on 100 watts input.
No output watt figures yet because accessories were moving around the table at that speed due to vibration.
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