Gamma Fan #2

Discussion on Stirling or "hot air" engines (all types)
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mhafele
Posts: 16
Joined: Sun Oct 08, 2017 10:27 am

Gamma Fan #2

Post by mhafele » Mon Jan 29, 2018 6:59 pm

5:1 ratio, will try same design with 1.5:1 next. Didn't get much better rpm between 20:1 and 5:1 with similar design.

What variables affect rpm the most? Thinking my vertical displacer might be too heavy.



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Ian S C
Posts: 2154
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Gamma Fan #2

Post by Ian S C » Tue Jan 30, 2018 4:13 am

My fan runs at 600rpm to 800rpm on the hot plate of an electric stove, power piston is 30 mm dia X 20 mm stroke, and the ratio is 1.5 : 1.
Ian S C
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mhafele
Posts: 16
Joined: Sun Oct 08, 2017 10:27 am

Re: Gamma Fan #2

Post by mhafele » Wed Feb 07, 2018 5:11 am

Ian S C wrote:My fan runs at 600rpm to 800rpm on the hot plate of an electric stove, power piston is 30 mm dia X 20 mm stroke, and the ratio is 1.5 : 1.
Ian S C
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Ian, how do yo decide on piston stroke? I've been picking a piston diameter by the available material available, using a random piston stroke, displacer dia based on material available and solving for displacer stroke.

Any methods for not just picking a piston stroke randomly?

Thanks for all the info.

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Ian S C
Posts: 2154
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Gamma Fan #2

Post by Ian S C » Thu Feb 08, 2018 1:57 am

I just pick a number and build, well not quite, I wanted a fairly small angle on the con rod, so the 20 mm stroke, this also allows reasonably high revs, and I think a short stroking motor does not need a very large flywheel, this motor uses the fan as it's flywheel, and the blades on that are quite light weight.
Long stroke : diameter, low speed, High torque. Short stroke : diameter, high speed, low torque, for motors of the same capacity, they should have about the same power out put at the crankshaft.
Here is the power head of the fan.
Ian S C
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mhafele
Posts: 16
Joined: Sun Oct 08, 2017 10:27 am

Re: Gamma Fan #2

Post by mhafele » Thu Feb 08, 2018 6:48 am

Ian S C wrote:I just pick a number and build, well not quite, I wanted a fairly small angle on the con rod, so the 20 mm stroke, this also allows reasonably high revs, and I think a short stroking motor does not need a very large flywheel, this motor uses the fan as it's flywheel, and the blades on that are quite light weight.
Long stroke : diameter, low speed, High torque. Short stroke : diameter, high speed, low torque, for motors of the same capacity, they should have about the same power out put at the crankshaft.
Here is the power head of the fan.
Ian S C
[img]
Test%20041%20(640x480).jpg
[/img]
Thanks, I read some where someone recommended the piston stroke to be equal to the dia. Any truth or science to that? I found the fan I posted above can run without the fan blade. The lobes alone on the crank shaft have enough momentum to keep it running. Also notice I took your advice and tig welded the top and bottom flange on the hot cap. It started on the first try with no tweaking.

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Ian S C
Posts: 2154
Joined: Thu Dec 02, 2010 5:15 am
Location: New Zealand

Re: Gamma Fan #2

Post by Ian S C » Fri Feb 09, 2018 3:21 am

Yes a square motor would be good(stroke = bore). A number of my motors will run without a flywheel, lots of revs, no power, but I think its quite a good test of a free running motor.
Ian S C

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