diy aquaponics aquarium | Stirling engines Slow motion balloon power piston

10.56 in Aquaponics, balloon, engines, motion, piston, power, slow, stirling

diy aquaponics aquarium

I made a few adjustments to my little tin can Stirling engine. It now spins twice as fast, at a rate of around 210rpm. Not that that means much because the more flame you put under it the faster it goes. But its around twice as fast as it was originally. Quite a success as far as bettering a terribly inefficient Stirling engine goes.

If you ask me.

The main adjustment I made was to replace the two sections of shaft that make contact with the supports. The original shafts and bearing surfaces were made of galvanised fencing wire.

I replaced them with a thinner grade of stainless wire. Actually its welding wire, and is the same stuff I use whenever I mention stainless wire in the construction of my fishing lures or anything else on the blog.

Pictured here in this uncomfortably framed, but interestingly red image, is the new wire, the old wire, and a match.

The thin stainless wire makes a huge difference. It even runs without the 8g counter weight now.

The counter-weight is there to mirror the weight of the displacer, so without it, the power piston has to lift all that weight on its own.



With the counter-weight and a minimum sized flame, it can now tick along as slowly as only 32 rpm.

Stately.

To run as slowly as 32 rpm, I found it also needed a small drop of very light lubricant (fishing reel/sewing machine oil). But its important to note that the shaft for the displacer - the one that goes through the small hole in the can, should not be oiled. The oil burns, and leaves a sticky residue which will stop the engine.  As seen by the improvement by the slight reduction in friction, the smallest extra friction will kill these little engines. Use graphite, or just leave it with nothing.

If you did lubricate the displacer shaft, its also possible that oil or Vaseline could get into the displacer container, and being flammable, might eventually find its way to igniting if everything was just right.

Everything is very rarely just right, and a Stirling engine is a very safe thing to make and use because there are no pressurised containers. The making involves some sharp bits of tin can, and should probably not be built by kids, but as a finished item, its as safe as any small candle is, so probably qualifies as relatively child friendly.

Lets say... As child friendly as a birthday cake.

Anyway, it looks like this in slow motion (sorry for the poor picture quality)...

[edit from the future - Opps, for some reason the video wasnt dropped into place.] Here it is...




Even more stately.

Its currently clunking away on my desk, running at around 60rpm on these two little flames, and has been doing so for an hour. One flame is about the size a birthday candle, and the other is around half the size of a birthday candle.

My point is it isnt using much heat compared to the last version.





I find its sounds...

oddly soothing.



K-chunk K-chunk



120 Things in 20 years thinks that if ever I disappear, it might be because Im off on a Stirling engined bike trip around Australia... in slow motion.




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diy aquaponics pdf download | Stirling engines Balloon Power pistons

12.40 in Aquaponics, balloon, engines, pistons, power, stirling

diy aquaponics pdf download

My original balloon power piston looked like this.

It had a connecting rod glued to the centre, and the other end of that rod connected to the cam shaft. The result was that as the air was heated in the chamber with the displacer, it expanded, filled this balloon, and pushed up the connecting rod.





I think it also pulls as the air cools and contracts, but that isnt very obvious either way. In that video (see link in first sentence) you can see the balloon inflating and giving the connecting rod a little push.

Im amazed that the air can expand and contract at such a high frequency. Im amazed these things work at all.

My power piston design was a little rough, and to be honest I was lucky that it worked at all.

The balloon kept slipping around under its rubber bands, making the connecting rod feel some resistance as the balloon reached its limits of free movement. The result was some extra friction where it wasnt necessary.

What I need is a bit more room for error.

With that in mind, I did some research and found what I think might be a useful design, and also came up with one myself that might work pretty well.

I found this one in use already and mine was made from a balloon neck, and a plastic bottle top.

To start with I created a plastic disk around 25mm in diameter by trimming off the sides of a plastic bottle cap. 

It was pretty easy to do with scissors, and a cut that went in a spiral gradually cutting away the side.

I also have a copper elbow that will be the power pistons basic form.

This will take the place of the ungainly plastic bottle with the hole hacked into the side as seen in the top-most picture on this post.

I cut the neck off a balloon and inserted the plastic disk. The connecting rod would be glued to the centre of this disk at the top.

The cut end of the neck is stretched over the copper elbow so that it looks like this when at its highest. (this would be the end of the power stroke)

And like this at its lowest.

It looks quite neat, and this is probably the design Ill use unless it proves to require too much air expansion to fill it.

My design includes the same section of balloon neck, and a cable tie to secure the top.

I tightened the cable tie with pliers  and then cut the rest of the balloon away with scissors.

It looks like this at its lowest. Or near its lowest.

It might be the case that this design will prove useful when used entirely at the low end. It requires much lass change in air volume to move 10mm up or down from its pictured position.







I have no idea if it will be of any benefit to use this (green) design, but It should be easy enough to try both with my adjustable cam shaft.




120 Things in 20 years - When it comes to balloon power pistons for Stirling engines, I have standards above which, I will not go.

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