Author Topic: Double acting Double cylinder Oscillator  (Read 30255 times)

Online Jasonb

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Re: Double acting Double cylinder Oscillator
« Reply #15 on: May 24, 2018, 06:57:37 PM »
The steeper angle of your design reminds me of the old air pumps often seen in labs


Offline Gas_mantle

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Re: Double acting Double cylinder Oscillator
« Reply #16 on: May 24, 2018, 07:09:28 PM »
Just a thought but would the cranks be better set at 90o to allow self starting ?

Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #17 on: May 24, 2018, 07:18:37 PM »
Gas_mantle--I did think of that, but decided for the sake of balance to leave the crank at 180 degrees. If this was going to be a real "working engine" I would make the cylinders from cast iron or bronze, and make the angle from cast iron as well, because of the high wear factor at the point where the cylinder face pivots against the angle. Since it will only ever live as a "demonstration" engine, the cylinders and pistons will still be made from cast iron, but the angle will be 6061 aluminum. The green colored end caps will probably be made from brass for a bit of contrast. The flywheel is massive enough that I am considering making it from solid aluminum.

Offline Jo

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Re: Double acting Double cylinder Oscillator
« Reply #18 on: May 24, 2018, 07:29:05 PM »
It's got the look of the Morton M5 about it or vice versa :)


That's the problem with doing models of real engines the same old thing crops up again and again  :facepalm:

Jo
Enjoyment is more important than achievement.

Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #19 on: May 24, 2018, 11:36:44 PM »
I've just been publicly whipped by someone on another forum. I had suggested that the engine would run "smoother" with better balance if the crankshaft was set up for 180 degrees. I was wrong.  With the crank throws at 180 degrees, you only get a power stroke twice in one full revolution of the crankshaft. With the crankshaft set for 90 degrees, you not only get self starting capability, you also get a power stroke every 90 degrees, so consequently the engine should run much smoother and slower with a 90 degree crank.---Brian

Offline Gas_mantle

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Re: Double acting Double cylinder Oscillator
« Reply #20 on: May 24, 2018, 11:55:06 PM »
When I suggested a 90o offset I reasoned it would run smoother but I kinda thought a relatively heavy base would be needed to dampen the uneven cylinder movement.

I can appreciate you are building a twin engine as a fun exercise and to look attractive but personally I'd want a twin to have an advantage over a single (whether that be self starting or smoother running) and to me a 180o twin is really little more than a single  :headscratch:

Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #21 on: May 25, 2018, 12:07:02 AM »
When I suggested a 90o offset I reasoned it would run smoother but I kinda thought a relatively heavy base would be needed to dampen the uneven cylinder movement.

I can appreciate you are building a twin engine as a fun exercise and to look attractive but personally I'd want a twin to have an advantage over a single (whether that be self starting or smoother running) and to me a 180o twin is really little more than a single  :headscratch:

We live---we learn. My first thought was that with a 90 degree crankshaft the engine would tend to "gallop" at low speed. I had that wrong. It might "gallop" if the cylinders were single acting, but with them being double acting, it should run smoother with a 90 degree crank.

Offline john mills

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Re: Double acting Double cylinder Oscillator
« Reply #22 on: May 25, 2018, 12:11:46 AM »
i like your engine but 180 degree or 90 degree is up to you 180 degree will be better balanced at high speed not self starting 90 degree will be self starting and run slower so thats for you to decide.
In full size engines there are both.you decide .its what you like.

Offline Gas_mantle

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Re: Double acting Double cylinder Oscillator
« Reply #23 on: May 25, 2018, 12:20:21 AM »
I'll follow along with interest, your threads always generate good talking points and give people chance to exchange ideas  :)

Looking back at the photos Jason posted, the green engine appears to have a 90o offset - admittedly the air pumps appear to be 180o but they are being driven from the crank so a balanced oscillation seems to make more sense in that case.
« Last Edit: May 25, 2018, 12:31:17 AM by Gas_mantle »

Offline 10KPete

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Re: Double acting Double cylinder Oscillator
« Reply #24 on: May 25, 2018, 02:50:56 AM »
Locomotives don't gallop...

Pete
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Offline Admiral_dk

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Re: Double acting Double cylinder Oscillator
« Reply #25 on: May 25, 2018, 01:12:28 PM »
Two cylinders and either 90 or 180 degree crank ….

90 degrees gives a smother torsional running - no matter if single or double acting and that is the reason why several modern two cylinder motorcycle engines are done this way …!... The negative side effect is vibration balancing - first order + rocking couple and this can be cured with a counter rotating balancer axel.

180 degrees has a bad torsional running as both pistons comes to complete standstill at the same time every 180 degrees. First order vibrations are canceled but you still has the rocking couple. A balance axle can cure the rocking couple, but not the torsional unbalance …!

Online Jasonb

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Re: Double acting Double cylinder Oscillator
« Reply #26 on: May 25, 2018, 01:29:55 PM »
As you are going to have to have removable cranks so the engine can be assembles it would beeasy to  try it with bot 90 and 180 degree settings and see what difference it makes to running.

Offline Gas_mantle

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Re: Double acting Double cylinder Oscillator
« Reply #27 on: May 25, 2018, 01:41:41 PM »
It looks like big oscillators for real work are set at 90o

http://www.shippingwondersoftheworld.com/oscillating_engines.html

Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #28 on: May 25, 2018, 01:43:30 PM »
Yes Jason--for the sake of one additional keyway in the end of the crankshaft, I am going to make this engine capable of running either/or 90 degrees and 180 degrees.
« Last Edit: May 25, 2018, 01:48:52 PM by Brian Rupnow »

Offline Brian Rupnow

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Re: Double acting Double cylinder Oscillator
« Reply #29 on: May 25, 2018, 06:04:16 PM »
This morning I priced out the material to build this engine. It was going to cost $155 for all of the material except the bearings. $50 of that was for brass, so I did a very deep scrounge of every bit of brass and/or bronze I have tucked away. I still had the top knob of that 50 pound bronze government weight that was used to check scales, and one lonesome piece of 2" bronze round stock x about 7/8" long. That actually yielded enough bronze to make four cylinder end caps. I have lots of little pieces to make the piston rod ends from. As soon as I have posted this, I'm heading out to buy the rest of the material.

 

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