Author Topic: Double acting Double cylinder Oscillator  (Read 30258 times)

Offline Gas_mantle

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Re: Double acting Double cylinder Oscillator
« Reply #210 on: June 18, 2018, 10:02:43 PM »
Brian, I like your engine and it seems a good runner but I don't think the difference in running speeds forward or reverse has much to do with the way it has been run in.

My guess is there will be some very small asymmetery in the way it has been machined. It would seem to me the probable difference will lie in the reversing gear, are the arc slots a perfect match ?

What does it run like in forward and reverse if you bypass the reverser but swap the inlet / exhaust connections ?

Offline Ramon Wilson

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Re: Double acting Double cylinder Oscillator
« Reply #211 on: June 18, 2018, 10:53:04 PM »
Congrats on a good result Brian  :ThumbsUp: glad to have been able to help in some small way. Thanks for the acknowledgement on the video - that's a first for me  ;).

The valve faces do need to be well lapped to each other and the mating should not be influenced by the pivot thread/tightening for best results ie the two faces need to pull up truly flat to each other.

Regards - Tug



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Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #212 on: June 18, 2018, 11:28:43 PM »
That is working great Brian, I think these can be operated by solenoids for boats etc. I have a question though, do you think there is a leak somewhere? It’s sounds a bit hissy compared to your previous video where I could hear a much more distinct exhaust beat.


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Nick--If I was deeply troubled by the hissing, I do have room for one more o-ring around the rotary disc, out beyond the air passage slots. I have shown a "standard size" 1 3/8" x 1 1/2" o-ring groove x .045" deep. I just don't know if it's worth the bother. It is difficult to buy individual o-rings in specific sizes.

« Last Edit: June 19, 2018, 01:52:17 AM by Brian Rupnow »

Offline crueby

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Re: Double acting Double cylinder Oscillator
« Reply #213 on: June 19, 2018, 01:03:28 AM »
An o ring there might make it worse, lifting the plate slightly and giving crosstalk between the ports, though if the center bolt is tightened that could be minimal. Seems like lapping would be enough.

Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #214 on: June 19, 2018, 01:49:43 AM »
Now that the excitement has died down a little, I have been analyzing what is happening here. The faces of the moving disc and the stationary part of the valve must fit tightly against each other at all times to prevent air loss.  This is not happening. When the engine is revolving in it's original direction, there is very little air leakage at the reversing valve. However, when I swing the handle thru a 90 degree arc to run the engine in the opposite direction, there is a lot more air escaping from between the valve faces, and that is the reason the engine is running slower, contrary to what I first thought.  I believe that the reason for this may be that the faces are held tightly together by a thread cut on the outer diameter of the pivot shaft and the inner diameter of the rotating disc.--I have never had a lot of luck getting a threaded connection so perfectly square to the rotational axis that the pressure is equalized all around. There are a couple of ways I can think of to make a better seal. One would be with an o-ring slot milled around the circumference of the rotary disc as shown in the previous post. The o-ring slot would be cut to about 75% of the o-ring's cross sectional diameter, so that when the threaded sections were screwed tightly together the o-ring would be for all intents crushed flat. Then if rotated thru 90 degrees and there was any loosening of the two pieces the o-ring would expand to "fill up the gap". That is probably the solution that takes the least amount of work.  A second way would be to remove any threads from the inner diameter of the rotary disc so it is free to slide on the pivot shaft, and have a longer threaded end on the pivot shaft with a small die-spring captured between the hex nut and the face of the rotary disc. I have to ponder this for a while to decide what I will do.

Offline 10KPete

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Re: Double acting Double cylinder Oscillator
« Reply #215 on: June 19, 2018, 03:02:29 AM »
Brian, that's a great engine!!  Congratulations!  :cartwheel:

Air leak: I found that, using your reversing valve for example, if you open the clearance hole in the disc so it's, say .02" (.5mm) bigger than the shaft, that it will no longer dictate position and let the disc sit flat on the mating surface. The radial positioning on the valve, or the cylinder of the oscillator, is much less important than letting the disc seat properly. Then a little spring will hold the seal tight.

I would NOT use an o-ring. Besides the o-ring trying to lift the valve off it's seat it introduces a drag element in to the 'shifting' of the valve. This is something the RC boat guys try to avoid because servos  have limited power.

The other part is making the seal surfaces mate right up to the passage ways, otherwise pressure can get in the much larger area and make more force trying to lift the valve off it's seat.

I hope I'm making some sense here....

Love your work!

Pete
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Offline Jasonb

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Re: Double acting Double cylinder Oscillator
« Reply #216 on: June 19, 2018, 07:47:35 AM »
Have the valve disc a free fit on a parallel pivot that is only threaded at the end for a nut with a spring under it, same as seals your cylinders so use the same simple method to seal the valve. That small O ring in Ramon's photo provides the small amount of "spring" pressure to hold his disc to the port face and it pivots on the plan section of the shaft, though he has it under the head of the shaft not the nut.

As said if you use the O ring as drawn and there is any lift between the face and valve disc air will just flow across the face from inlet to exhaust as the o ring expands to fill the gap.

« Last Edit: June 19, 2018, 08:03:16 AM by Jasonb »

Offline NickG

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Re: Double acting Double cylinder Oscillator
« Reply #217 on: June 19, 2018, 11:07:44 AM »
I agree with the guys, well lapped surfaces, clearance in the pivot hole and spring to keep them together. In off position spring needs to be strong enough to prevent the pressure from pushing discs apart.


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Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #218 on: June 19, 2018, 02:06:25 PM »
Okay Guys---Good advice. I drilled the threads out of the rotary disc, and opened up the 1/4" diameter that was a "precision fit" on the 1/4" pivot shaft x about .005" . I found a couple of  little compression springs and captured them under the hex nut so they bear against the front side of the rotary disc. This is going to work, and quite well I think. It still leaks a bit around the edges of the disc, but it's dramatically reduced.--And--If I apply a little more pressure with my thumbs on the face of the disc, the air leakage totally stops. I will go down to the company where I buy my springs and pick a heavier compression spring this morning. The compression springs I have on hand are a bit wimpy, but are strong enough that I believe this operation is going to be a success. thank you for the advice and suggestions.---Brian

Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #219 on: June 19, 2018, 03:42:27 PM »
Just got back from my spring people with a very stiff little compression spring and installed it under the hex nut. The air leak is completely gone.---And yes, it runs the same speed in both forward and reverse. The new spring is 0.040" diameter wire x .3125" outside diameter with a 0.050" pitch when free and a free length of 1.1".  In it's fully compressed state it is 0.350" long. Again, thank you to everyone for their help.---Brian

Offline 10KPete

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Re: Double acting Double cylinder Oscillator
« Reply #220 on: June 19, 2018, 05:04:53 PM »
 :ThumbsUp: :cartwheel:

Pete
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Offline NickG

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Re: Double acting Double cylinder Oscillator
« Reply #221 on: June 19, 2018, 07:33:30 PM »
Brilliant, nice work Brian. Will you have time to do a final video?

I’ve just seen two cast iron brake cylinders that were the wrong ones for my car in garage and it got me thinking about big wobbler cylinders! There’d be a few holes to block though - do able or a waste of time and better starting from scratch?!


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Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #222 on: June 19, 2018, 07:38:20 PM »
Nick--I've seen it done, but--Considering the low cost of round cast iron, you would save $20 worth of material to do 50 hours of extra work. Yes, I will put up a final video. I'm machining a fancy "bullet" nosecone right now to cover the spring and hex nut.---Brian

Offline NickG

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Re: Double acting Double cylinder Oscillator
« Reply #223 on: June 19, 2018, 07:58:51 PM »
I was thinking the basic shape and the bore is there, would it save a lot of machining or could just cause more needing to block up holes etc!


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Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #224 on: June 19, 2018, 09:03:37 PM »
I don't advise it.---Then again, I don't make the rules. Try it and see. You have nothing to loose but your time.---Brian

 

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