Inspiration for new air motor

[Brian Rupnow]

This animation shows the valve and valve mechanism in place and operating. I believe I have found good mechanical solutions to everything. Nothing "crashes" during a 360 degree rotation. The nearside flywheel is "hidden" in order to clearly see all of the parts moving. The only part I am unsure of is the valve. I re-used the eccentric cam and the valve body and valve slider from a running engine that I have, but due to the strangeness of this engine, valve events are not occurring when they should, and I don't have enough experience with valving to correct it.  If anyone with experience wishes to step up and help me with the valving, the engine will be built. In return for that help I will give them a complete set of plans for this engine. If not, it will just remain an interesting design exercise.---Brian
<a href="https://www.youtube.com/watch?v=FhpR4OAYmnQ" target="_blank">http://www.youtube.com/watch?v=FhpR4OAYmnQ</a>

[Jasonb]

It's really just a case of timing the valve to the piston, forget the crank and its linkages as it just complicates things.

You want the air to start filling the cylinder just after TDC and to have closed Just before BDC. Exhaust to open just before BDC and close on TDC. This makes sure the engine can push out all the spent air before the next lot if let into the cylinder.

I don't know if that valve allows for zero overlap but the above is how I have the single acting Jowitt Poppet valve engines set and they run well. If you can't get zero overlap then have less intake but keep the exhaust open so it does not slow the engine.

[Alyn Foundry]

I agree.

We had a few " Desmodronic " style cams made from an exact copy of the Ernst Plank engine that I have.

Using this method means you don't have any unnecessary springs to " sap " energy.

Cheers Graham.

[Brian Rupnow]

I feel a bit foolish even having to ask. I am supposed to be "SuperDesigner" and know all this stuff. I know what I want to happen, and I know when I want it to happen. I'm just not sure how to get there. Really, about the only variable is the offset of the eccentric and the length of the link directly above the valve itself. The rocker is equal length from the pivot shaft to the center of the crankshaft and to the center of the valve when taken in a horizontal plane. That exact same eccentric, valve, and valve body works fine on the Chuck Fellows engine that I built about 10 years ago, then modified it from Chucks valve design to mine. I am moving all of the inter-related parts with my Solidworks, but I'm not getting the same positional results with this engine.

[Brian Rupnow]

I've just realized that my valve sequence may seem a bit funky because with the pivot in between the crankshaft and the actual valve, the valve action is reversed from what the original motor was.  Now I have to try and decide what that information actually means to me. Last night I printed out five pages of valve positions from the original motor, to determine where the valve was when the piston was at top dead center, bottom dead center, halfway thru its stroke going up and coming down, and what things looks like at 45 degrees past dead center travelling counter clockwise. I'm 99% certain that if the cam, valve, and valve body worked on one single acting engine, it should work on another single acting engine, even though the piston stroke may change from on e engine to the next.

[Jasonb]

Yes should still work. You probably want the eccentric about 270 different to whats on the small engine. 90 degrees due to the valve being vertical and not horizontal and 180deg due to the rocker reversing the direction.

[Brian Rupnow]

I'm pretty sure I have the valve sorted out, thanks to some help from Jason. Now if I get really, really, really bored this summer, I have something to work on.

[crueby]

This summer? I am betting on this next week...!   

[dpaulson]

Brian 
Looks like something I would like to build
Will follow along

[Brian Rupnow]

Sometimes it is a bad idea to make too much of a change from whatever engine inspired you in the first place. I didn't like the look of the feet that I had on the model, so I changed them to be more or less the same as the flame-eater engine in the first post of this thread.

[crueby]

Neat looking. You could call it the Elephant engine, four big feet, flywheels look like ears, rocker is trunk, though the flame up the butt is an issue...

[Brian Rupnow]

Call it the elephant that's been eating Jalapeno peppers!!! 

[Brian Rupnow]

I have a theory on engine building that goes like this. Take the awfullest, most miserable part on the whole job and do it first. If you can do it successfully, then anything that comes after will be easy. The block that holds the crankshaft bearings and the pivot shaft is the hardest part on this engine. I rooted around in my box of aluminum and found a piece big enough to do what I wanted. This is kind of a trick, because you need a considerably larger piece to start with than what you finish with---especially if there are radii near the perimeter of the piece. You can't drill half a hole, so the stock needs to be large enough to leave about .100" beyond any holes that are drilled to give these radii. there are four holes to be drilled here. A 1" dia. hole on the right to give the radius I want. A reamed 3/16" hole in the upper left corner for the pivot shaft, a 3/8" hole below that to give another radius, and the center hole, bored to 0.906" for a bearing fit. You can actually see the bearing setting in there in the shot on the mill. I drilled that hole to 27/32" and bored it the rest of the way.

[Admiral_dk]

OK Chris officially won the competition about how long it lasted before you couldn't stay of the chips Brian     

[Brian Rupnow]

Some quality time with my friend the bandsaw yields a part that is starting to look like the drawing.