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Old 11-19-2008, 10:56 AM   #11
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Default Re: How Slow Can You Go

That's beautiful Paula!




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Old 11-23-2008, 04:04 AM   #12
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Hi again!

Well, I finally got my compressor up and running, so I took a short video of my D & M #11 engine in action. It's running on around 5-7 PSI, with the throttle set to run just fast enough to give a smooth motion. (It will run slower, but in a rather herky-jerky fashion):



Much faster than Bret's engine, I'll grant you. No doubt the main reason is the two 1/16" wide cast iron piston rings, comprising fully one-half the length of the piston. I made it per the drawings, but knowing what I know now, I probably would have used an oil-grooved (ringless) piston, like the one specified for my Stuart 10V. Particularly since this is not a "working" engine, but an occasionally-run "shelf queen". Still, I'm very pleased with how it runs. At higher speed and pressure, it puts out very respectable torque. I only wish that I had known (or cared) how to balance an engine when I built this one.

All comments welcome

Paula


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Old 11-23-2008, 05:10 AM   #13
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Default Re: How Slow Can You Go

Paula and bretk,

That is three very nice engines

Paula, whats wrong with the balance?

Best Regards
Bob
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Old 11-24-2008, 02:13 PM   #14
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Default Re: How Slow Can You Go

Thanks, Bob!

Quote:

...whats wrong with the balance?
At higher speeds, the engine wants to jump around bit. There is a cast-in counterweight feature in the crank disk, but it doesn't seem sufficient to accurately balance the rotating and reciprocating weights. It was only after completing this engine that I learned how to balance an engine properly (I.E. -- I read an article ) However, since the goal with these engines seems to be to run as slowly as possible, high-speed balancing seems a non-issue.

Cheers,
Paula



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Old 11-24-2008, 07:35 PM   #15
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Default Re: How Slow Can You Go

Paula,

Thanks for that. The reason for my question was my concern re balancing my small 1 pot IC engine.

To give it a somewhat rudimentary check I ran it flat out using a drill. I was pleased with the lack of jumping around but the drill is at best 1/4 - 1/2 the operating speed.

It looks like a suck it and see exercise.

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Bob
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Old 11-24-2008, 08:07 PM   #16
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Default Re: How Slow Can You Go

I have a hit n miss engine that is 1" bore and 1.5" stroke. I balanced it by placing 1/2" neodymium magnets on each of the flywheels, opposite the connecting rod journal, on the inside step of the outer rim. I kept adding magnets side by side until the engine would run with no noticable vibration. Someday, I'll weigh the magnets and make steel plates to attach to each flywheel. For now, the magnets work fine and show no tendency to fly off. I can provide a picture if anyone is interested in seeing it.

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Old 11-27-2008, 08:44 PM   #17
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Chuck, that's a neat idea!

The method I've used is based on an old article in "Strictly I.C." magazine, by Richard Condon. Basically it states that, for the lowest bearing load and minimum vibration, you want to counterbalance all of the rotating weight + 1/2 of the reciprocating weight (you need an accurate scale for this):

1) Weigh the big end of the connecting rod (place the crank-end on the scale, whilst the piston-end rests on a fixed surface)

2) Weigh the crank bearing (if there is one)

3) Add the above two weights to equal the Total Rotating Weight (TRW)

4) Weigh the piston, pin, and ring(s) to equal Reciprocating Weight (RWT)

5) Weigh the connecting rod (without bearing) to equal Weight of Connecting Rod (WCR)

6) Receprocating Weight (WR) = WCR + RWT - TRW

7) Balance Weight (P) = .5(WR) + TRW

With the crankshaft (or crankshaft-flywheel assembly) resting on knife edges, hang a weight equal to P from the crank pin. The crank assembly should balance the weight. If not, apply weights, drill holes, etc. to achieve balance. That's it.

On my Odds'n Ends engine, I elected to do three things to balance the crank:

1) Made bolt-on counterweights for the crank:



2) Drilled out the crank pin, and

3) Chamfered the crank throws:



There is definitely some trial-and-error involved in getting the crank to balance the P weight. If you know Statics, and calculating density of materials, you should be able to save some time here.

It worked like a charm for me -- on several engines.

Paula
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Old 12-27-2008, 08:56 PM   #18
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Nothing better than the quiet magesty of a slow running engine. it almost makes me cringe when I see people 'tacking up" their model steam engines until all you can see is a blur of rods and wheels. they look so much better running slow.
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Old 12-27-2008, 09:41 PM   #19
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Default Re: How Slow Can You Go

I'm with you loggerhogger on that. I've been able to build a steam (air operated) engine that will rotate at 60 rpm. That's the best I can do to this point. I hope when I put more hours on some of them I'll be able to get them running slower.

Cheers,
Phil
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Old 03-03-2009, 04:30 AM   #20
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Default Re: How Slow Can You Go

Again I'm resurrecting an old thread, but when I first read it I kept it in the back of my (convoluted?) mind. One of my aims in building an engine is always to see how slow I can run it.

During the recent Cabin Fever Expo I picked up some needle valve air flow controllers. These valves allow really fine air control. I set up two of my engines that had some break-in time on them. From my compressor I have ¼” air hose going to a 1/8” NPT line that connects to the flow control. Out of the flow controller I have 3/32” OD polyethylene tubing of 0.105” ID going to the intake of the engines.

The engine shown here has a 1.5” bore x 2.1” stroke and is double acting. The flywheel is 6” diameter. I’m able to run it at about 50 rpm.


The engine shown here has a 1.25” bore x 1.8” stroke and is also double acting. The flywheel is 6” diameter. I’m able to run it at just shy of 50 rpm.


I think this will be the best I can do with this design but I am still wondering….what’s the lower limit. Has anyone constructed a model engine (air or steam powered) and run it at 10 rpm or less? I feel like Monty Python and the Holy Grail here.

Cheers,
Phil





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