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Overview

This is the third Stirling engine that I have built. It is made after the plans from Darryl Boyd on http://www.boydhouse.com/stirling/index.html . Go watch the plans plus very many pictures of models that other people have built.

Construction: Displacer

These pictures show the view of the finished machine and the construction of the displacer.

Click on the thumbnails to enlarge the photos:

01totalview.jpg

02animated.gif

03displ_can.jpg

01totalview

02animated

03displ_can

04displ_btm_unsoldrd.jpg

05displ_btm_soldered.jpg

06displ_top.jpg

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05displ_btm_soldered

06displ_top

At a later time I may replace the 'heavy' tomato can as displacer piston with a lighter and better fitting one, maybe from balsa wood or an aluminum can, to speed the machine up a little.

For most of the parts I have used recycled material. The walking beam, the main engine and the flywheel support are made from an old wooden book shelf.

Power Piston

Next you can see the power piston, that a friend has made for me on his lathe.
Photo 8: I used my small Unimat lathe to make a good fit between the power piston and the power cylinder. I made a large excenter disc to move the piston often with some polishing powder and oil between the surfaces. 

07pwr_piston.jpg

08grind_pwrpiston.jpg

09pwr_piston_in_pos.jpg

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08grind_pwrpiston

09pwr_piston_in_pos

Power and Displacer Cylinders

Photo 10 shows the hand filed fit between the two, for which the software "Winmiter" was a great help. Pic 11 shows my drillstand being used as fixture for soldering.

Photo 16: the top of the display cylinder was not soldered to the body, but fixed with some wire (see photo 01). It is airtight due to a rubber gasket in the top rim.

10pwr_cyl_fit.jpg

11piston_cyl_fixture.jpg

12piston_cyl_soldered.jpg

13piston_cyl_view.jpg

10pwr_cyl_fit

11piston_cyl_fixture

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14displ_cyl_inside.jpg

15displ_cyl_outside.jpg

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17water_tank_soldered.jpg

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Flywheel and rods

For the bearing of the flywheel I used the head of a dumped video recorder, which shows nice details of the synchronous head motor. The rods are made from bicycle spokes, connected with round electrical terminals crimped then soldered to the rods (idea from Rex James, Australia).

Click on the thumbnails to enlarge the photos:

18test-flywheel.jpg

19flywheel.jpg

20flywheel_videohead.jpg

21rpm_reading.jpg

18test-flywheel

19flywheel

20flywheel_videohead

21rpm_reading

I made some experiments with the length of way that the power piston travels (rod positions 1 to 5 in pic 18). Too short is obviously not good, but too long as well. To study this, I added the blue mark on the slotted hole of the horizontal rod (arrow). Flashlight photos unveil what happens. I noticed the piston being sucked back in (to the left) while the piston was still being moved to the right from the flywheel when the travel distance was too large.
For these experiments I used a 100W light bulb as a heat source: my spiritus flame was not constant enough to tell the differences of my adjustments.
After the tests with the CD stack I used a plexiglass disk as a flywheel, enhanced with a reflective foil (pics 01 and 02).

Tachometer

As something special I added the computer from my bicycle, which has a cadence sensor. I just added a reed contact and a small magnet to the flywheel, and voila, the readout is directly in rpm (revolutions per minute). See photo 21. A bike computer without cadence sensor can be used with less accuracy: set the wheel circumference to 1666 mm: the speed reading 6 km/h means 60 rpm.

Performance

The maximum safe engine speed was around 150 rpm. It was a bit higher once, but the soldering of the fire box disintegrated due to too much heat. Next time I would use a better solder (braze) for the fire box and the power cylinder.

The machine took a while to be finished. Collecting the material was quite time-consuming. The construction phase was finished in August 2006.

As a summary, it was not easy to make the machine run well. Friction must be minimised everywhere. But it was a lot of fun. Thanks, Darryl, for the plan and your great website.

Dimensions

Power piston diameter: 18 mm
Power piston travel length: 42 mmm
distance crank point on fly wheel to center: 21 mm
left arm of walking beam: 147 mm
right arm of walking beam: 145 mm

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