I got 2 cylinders with push rods and cam assembled in a case. I changed the cam to a smaller one, cut from 1- 3/4" dia rod, so it is as smooth as glass. Pistons can now spin the shaft, now I need to add a flywheel to see if I can get it running. I have to be careful because it is still using polyethylene bags, so I have to limit the temperature.
Here is a picture of the partially completed prototype, but with the old cam.
Since I am using low pressure air as the working gas, the stresses on the push rods is not too bad. But I will need to add the cam follower guides so prevent the rods from bending when the press down on a inclined section of the cam with higher pressures.
I found a 7" flywheel pulley on my old vacuum pump. It had a 5/8" hole for the shaft, but I had a 1/2" bearing that had a 5/8" OD to adapt it. There is still not enough inertia to make on rev, so rather then getting a bigger flywheel, I've decided to complete the other 2 cylinders to balance the forces. Since they were always in the plan, might as well build them and test the entire unit. I will complicate matters having to apply heat and cold to 2 sets of cylinders. The other option would be to buy a larger flywheel from Grainger for $50. I guess I want to see it running before pouring more money into the project. I'll post a new picture soon of the assembled 2 cylinder version.
3 comments:
Can you please tell me how you made the pistons
I have been interested in Stirling Engines for about six months. Recently I set up a google alert for anything that's published with "Stirling Engine" in the text. I've got to say I'm fascinated with what you are doing. What a wonderful achievement if someone could design low power engines built with "off the shelf" components. I'm going to be waiting with anticipation for updates. Good luck Tom!
Tom Shelton
Hi serbus,
The pistons are the most complex part of the machine.
For the 2" (actually 1.96") diameter piston, I am using 3" wide by 6" long polyethylene bags.
The actual width is a little over 3" so the bag is too loose over the piston and creating wrinkles.
Assembling them is a pain even with polyethylene bags. I have to stretch them out to get it over the outside of the cylinder. Luckily LDPE stretches easily, but when it comes time to switching to a tougher material it is going to get much harder, unless I can pre-stretch them to size.
The piston has an inner core of 2 cyclinders of 1/8 wall plastic, through which the wrist pin goes through. The outer sleeve is a turn down tube and is held in place on the core with set screws from inside the core.
There are 2 disks at the top, to seal unit and one outside the bag to hold it in place.
Once I see this thing running, I will start publishing more details, but at this point I am just looking to see how much interest there is.
I will contact you through your blog once it comes together.
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