Stirlingengineforum.com

Hello everyone!

I developed a "new" crank design in the last few months for a beta type Stirling engine.
Started point was a triangle yoke design, follow A. Ross earlier works.
After optimized step by step the mechanism part's dimensions.
I knew the Ruby crank design, but there are lot of differents:
The power piston drive a simmetric "L" yoke---mine drive the straight yoke also this part is a force duplicator.
The attack points are so different. The strokes are different long there.
Mine "L" yoke is assimmetric, and the strokes are similar, no different, so the compression ratio is high.

If you can check my video about a basic rhombic drive vs. my 105° "L" yoke drive system, then you can see the phase difference are so close to them.
The rhombic drive has 6 parts, mine only 3, so I think it will be cheaper, but good enough for a good performance beta engine.
I've been try to syncronized this two mechanism movement in one screen, but I'm not expert in Corel video studio, so it was hard to make.

What do you think about my drive mechanism?

[BBvideo 425,350]http://www.youtube.com/watch?v=ecEVkOiU3Yw[/BBvideo]

Not too clear Blade, have you got a photo of a working model, it might be easier to see how it works. From what I can see, a simple crankshaft would be easier, perhaps with the displacer driven via a Scotch Yoke, which is a good way of shortening the length between the displacer and the crankshaft. It can be used on the power piston, but the friction is high on the power side compared to the displacer/driven side of the motor. Ian S C

Why better a photo? The CAD is perfect for simulate the whole movements.
The mechanism with 90 degrees "L" shaped yoke on a normal also on a closer view:
[BBvideo 425,350]http://www.youtube.com/watch?v=lnvhYz3iasQ[/BBvideo]
[BBvideo 425,350]http://www.youtube.com/watch?v=6ZLfyWwUWpI[/BBvideo]
But the 105° is a little bit better.

The simple crankshaft is always fixed the phase angle, and not the 90° is the best. That is a compromised angle.
The normal crankshaft has a big friction on the power side. If the strokes are perfectly same and long then the piston's rod should be long too.
The Ross yoke is not good for a long stroke engine, but the phase angles are change all the time of rotation.
And I never seen Ross yoke beta engine!

If I need a short stroke, then the whole mechanism will be shorter, smaller.
Actually it has long strokes.

Same mechanism as Allan Organ's hairdryer engine.

NHH

Not quite a CAD animation I'm afraid, but here is a variation that I mocked up a few years ago which gives straight line motion at one of the drive points in the manner of a half beam or 'grasshopper' steam engine.

I'm not pretty shure about A.O.'s engine, but everything is possible... ( Do you know the Hundredth monkeys effect? :) )
I seen some alpha type engine, but beta type I never seen before from him.

Your mechanism is nice, but the strokes are different.
That was the point why I started to develope for myself this mechanism.
I wanted to make a pretty same movement as a beta rhombic drive, with changed phase angles.

The 90° symmetric "L" yoke is never been enough good for this criteria.

Yes, not so good in some ways though unequal strokes is not necessarily a problem. I started with all the lengths equal for simplicity - more difficult to make changes when you are cutting metal rather than using a computer! Then, as is usual for me, once I had demonstrated it 'sort of' worked, I moved on rather than developing the idea.

I can't find an illustration of AJO's hairdryer motor on the net, it is described in his book 'Air Engines' and I think he mentions that he did not originate the mechanism - the monkeys had been at work already!

NHH

There seems to be very little, if anything that is actually new in this world.
If you look at the 2.5cc motor in my gallery, this is my version of a motor by Justin Jones, in Model Engineer magazine in 1997, there were two versions BETA, and the other GAMMA, both of these motors use only one crank pin, the power piston acts directly on the crank pin, the displacer is driven by a bell crank. This motor has a power stroke of 1/2" and a bore of 5/8", the cylinder is brass, and the piston is aluminium with a Teflon sleeve. The original of this motor won the Gnat power competition at the Model Engineer Exhibition in 1996. Ian S C