Inspiration for new air motor

[Brian Rupnow]

I really, really, don't want to start another build right now. However--I have been researching all of the many different flamelicker engines, and ran across the Bengs unit. My God--It's awesome!! I wouldn't want to build a flamelicker engine, as I now have finished the Poppin by Dr. Senft, and a Stirling engine which was 75%Moriya fan and 25% me. I have I.C. engines out the ying yang. and a goodly number of air/steam engines. I really like the style of this engine, and may design a single acting air motor based on this.

[ame]https://www.youtube.com/watch?v=0G4OuBVb7NY&feature=youtu.be[/ame]

 

[Brian Rupnow]

I find it strange that the rocker arm isn't set at a 1:1 ratio. It looks like the distance from the piston rod to the pivot is twice as long as the distance from the pivot to the connecting rod. I'm trying to wrap my head around that. I don't think it changes the number of flywheel revolutions to cylinder strokes. I think it just means that you can get away with a shorter throw on the crankshaft.

 

[TonyM]

The ratio looks about 2:1 so maybe half the effort to turn the flywheel.

 

[Barnbikes]

I could see you building this one.
[ame="https://www.youtube.com/watch?v=YZMBFG9Eyzw&t=53s"]https://www.youtube.com/watch?v=YZMBFG9Eyzw&t=53s[/ame]

 

[Brian Rupnow]

I have the engine all designed---in my head. The only thing I'm not sure of is the valve mechanism. Since it will only be a single acting engine, it doesn't really require a sliding admission valve like you would find on a double acting cylinder. Probably a simpler valve driven by an elliptical cam through a couple of bell crank mechanisms would work. I have an old Chuck Fellows single acting engine that I converted from it's original design to operate with a valve like this. I'll have to see if I still have the drawings of my design changes to Chucks original valve mechanism. Other than the double acting twin Stewart engine I built this winter, it's been a long time since I messed around with air/steam engines.

 

[Brian Rupnow]

Ah Rats!!! I can't find the files I need. I thought I had them on a disc, but after a massive disc hunt I can't find them. I do have the original files of Chucks hit and miss engine, but not the changes I made to the valve system.--However, it's not a major issue. I have the engine here on my shelf and I can pull it apart and reverse engineer it.

 

[Brian Rupnow]

Okay---We're good!! I took the old single acting engine down of the shelf and did a little reverse engineering. Now I know exactly how the valve for a single acting engine works. (I had forgotten). This is the valve my new creation is going to use. It is a very versatile valve that can be mounted any number of different ways.

 

[Brian Rupnow]

Where do you start with something like this? Well in my case, I happen to have a pair of 4" flywheel rings that at one time were mounted on my Kerzel engine. They didn't improve the hit and miss action of the Kerzel, so they were saved for a future project. This may be it. Second consideration is ratio and proportion. If you look at a side view of the flame-eater engine I am copying the style of, you will see that there is a ratio between the outer diameter of the flywheels, the outer diameter of the cylinder, and the length of the cylinder. There is also a relationship between the center of the flywheels and the centerline of the cylinder, both vertically and horizontally. This is somewhat subjective. And of course we know that the flywheels have to be placed far enough from the center of the cylinder that they won't rub on it.--So, for now we place them where they won't hit the cylinder as they revolve. That's what is involved in the "starting point" of a layout .

 

[Mechanicboy]

I find it strange that the rocker arm isn't set at a 1:1 ratio. It looks like the distance from the piston rod to the pivot is twice as long as the distance from the pivot to the connecting rod. I'm trying to wrap my head around that. I don't think it changes the number of flywheel revolutions to cylinder strokes. I think it just means that you can get away with a shorter throw on the crankshaft.

With large piston stroke + diameter transfered power via rocker arm who are pivoted in 2:1 ratio will give larger torque in crankshaft.

 

[Brian Rupnow]

Of course we are going to have to have a couple of supports to hold this engine up off the tabletop. This calls for milling a couple of 1/2" wide slots in the bottom of the cylinder and making up a pair of stands that will bolt to the cylinder. Right now the supports look kind of long and skinny, but the reason for that is to let the ends of the mount stick out far enough past the outside of the flywheel that I can reach down beside the flywheel with my screwdriver and put a #8 woodscrew through each of the four holes to mount this puppy to my workbench.--Don't want it to walk away on me when it's running.

 

[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.

 

[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". Now I have to make this. I will try and put up an animation.

 

[Brian Rupnow]

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

 

[kiwi2]

Hi Brian,
It may be worth while designing the steel rim of the flywheel to be consistent with the dimensions of say schedule 80 pipe. 3 1/2" schedule 80 steel pipe has an OD of 4" and a wall thickness of 0.318" while 4" schedule 80 pipe has an OD of 4.5" and a wall thickness of 0.337". The 4" material is likely to be more readily available than the 3 1/2".
Regards,
Alan C.

 

[Brian Rupnow]

Hi Brian,
It may be worth while designing the steel rim of the flywheel to be consistent with the dimensions of say schedule 80 pipe. 3 1/2" schedule 80 steel pipe has an OD of 4" and a wall thickness of 0.318" while 4" schedule 80 pipe has an OD of 4.5" and a wall thickness of 0.337". The 4" material is likely to be more readily available than the 3 1/2".
Regards,
Alan C.

Have a close look at post #8.--I already have those outer flywheel rings left over from a different project.

 

[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]

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
[ame]https://www.youtube.com/watch?v=FhpR4OAYmnQ&feature=youtu.be[/ame]

 

[johnmcc69]

It seems your cam is not rotating at the same speed as the crankshaft in your animation.

John

 

[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.