Inspiration for new air motor

[Brian Rupnow]

We need a piston. There's a lot going on with a piston. The cylinder bore is .875", so we want our piston to be a "precision sliding fit" into the bore. A good enough fit that it won't fall through under gravity, but will go through with a gentle push with your finger. We don't want our piston to "cock sideways" in the cylinder, so we make it  "a bit" longer than the diameter. There isn't going to be any rings on this piston, but we need two shallow grooves around it for oil retention to help prevent air from passing around it. We want the hole for the wrist pin to be less than halfway from the closed end of the piston. This again is a measure to prevent "cocking sideways" in the cylinder. we need a slot wide enough for the connecting rod to fit into, and we want to releave a lot of material from the open end of the cylinder to prevent the con-rod hitting the inside of the skirt when it is at it's most extreme angle.

[crueby]

Great to hear your comments on your design process as you go, great stuff!

 

[Brian Rupnow]

What can I say about flywheels? The easiest flywheels to make are from aluminum. But--aluminum just isn't heavy enough to make a good flywheel. However, a two piece flywheel with an aluminum center and a steel outer rim work really, really well. For the artistic among us the holes in the center can be just about any shape, even the creation of curved or straight spokes is possible. Just a note here in an area I've been burned on before. Make the hub diameter large enough that you have at least 3/16" of material between the centerhole and the outside of the hub, or your set screws are going to strip out. If you have a keyway, then make your hubs large enough in diameter to allow at least 3/16" between the outer limit of the keyway and the outside of the hub, or again, your set screws are going to strip out. I like to put two set-screws in each flywheel, 90 degrees apart. If I have a keyway, then one set-screw sets over the keyway and the second at 90 degrees from it. And finally--although it isn't really critical, flywheels look a lot better with the "spoke area" relieved about 1/3 of the flywheels thickness on each side as I have shown.

[Brian Rupnow]

Well sir!!! I'm surprised right outa my pants. I have input the geometry based on a 2:1 ratio in the pivot lever, and it works. The crank "throw" is 1/2", but because of the 2:1 ratio in the pivot lever, the piston actually travels 2". one flywheel is currently hidden. Now I have to make this. I will try and put up an animation.

[Brian Rupnow]

This is going to be amazing.
https://www.youtube.com/watch?v=SgS8hpX75B4&feature=youtu.be

[b.lindsey]

To be " really,really not wanting to start another build," you are sure diving into this one Brian. I agree though it is a very compelling design.

Bill

[crueby]

Has anyone made a twin cylinder version of one of these kinds of engines? A twin of this style would be fascinating to watch. Though probably a bear to get to run right.

Anyway:
Got my popcorn ready to go!   

[Jasonb]

The monitor engine is not unlike a twin cylinder version. Just the rocker arm is not straight but two arms on teh same pivot and crankshaft sits lower. Still the same principal just a lot more detailed than this simplified one.

[Alyn Foundry]

Has anyone made a twin cylinder version of one of these kinds of engines? A twin of this style would be fascinating to watch. Though probably a bear to get to run right.

Anyway:
Got my popcorn ready to go!   

Yes....

A twin cylinder CHUK inverted vertical was tried but the " Bear " still rules!!

I also sketched a design for an inline " four " with manifolded intake, a pipe dream perhaps?

Cheers Graham.

As a " post script " Brian's creation would lend itself nicely to a twin piston with common bore....

[Ian S C]

You could make the motor with two pistons in the one cylinder, with a rocker at each end, the two con rods would operate on the one crank pin.
Ian S C

[Alyn Foundry]

You could make the motor with two pistons in the one cylinder, with a rocker at each end, the two con rods would operate on the one crank pin.
Ian S C

Forgive me Ian.

But wouldn't that be counterproductive? You'd have one piston going in and the other going out. As I see it you want both pistons working in unison, we made a single IC engine called the Moffat that used dogleged rockers off a 180 degree double throw crank.

Cheers Graham.

[Brian Rupnow]

I'm all ready to go on this thing, except for the valve which operates off a cam on the crankshaft. I have a terrible time with the valving on these things because I don't do many of them. I have the valving on normal double acting cylinders sussed out pretty good, but these single acting ones make me a bit crazy.

[Brian Rupnow]

To be " really,really not wanting to start another build," you are sure diving into this one Brian. I agree though it is a very compelling design.

Bill

Bill--Thats my life. If I don't have engineering work to do for a customer, then I have nothing to do at all except design or build something. I don't watch much TV at all, and I read but right now I'm waiting for all my favourite authors to publish. I just love designing, and somehow I don't feel commited with designing like I do when I actually start to cut metal. Once I start cutting metal then it picks me up and won't let me go until I have an engine.

[b.lindsey]

I totally understand Brian, and my comment was not a complaint at all    It's amazing how the gears start turning once a new idea gets into our brains 

Bill

[Brian Rupnow]

Bill--Once I get a new idea like this my head catches fire!!!