Home made toys

[marki]

It's raining here again so I pulled out some toys I made last year and played with them:P. I like to dabble in metal work and have my own lathe and mill and a real soft spot for heat engines (stirling engines). I have chucked a few pics of a couple my engines up here to see if anyone else likes to make these. One is powered by ethanol and the other by a cup of hot water or a block of ice. The trick to making these engines is to keep the friction down as much as possible and get the timing right. When I first started making them I had to use exotic materials to get them to work but now have it down to a fine art and can get away with more readily available stuff. The ethanol powered engine will rotate at around 750RPM but if I use an gas torch will reach as much as 1500RPM before the hot cylinder melts:P. It will also spin up to about 500RPM using the sun and a fresnel lens. The low temperature version spins up to about 200RPM on a cup of coffee :). This engine was great fun to make as my students had a large input in getting the design right (vectors, forces, gas expansion and contraction etc). Should have seen their faces when the engine ran for the first time on a block of ice :D. We also designed a hot water tank using cotton wool, polystyrene and an old milo tin. When placed on this the engine will run for about 8 hours.


Mark

[DavidU]

Great stuff ! I love this sort of thing.

[TrevorW]

I'm glad you could get your Stirling to work do you want a near frictiionless glass piston for your next one

Cheers

[marki]

Yep I will have it :thumbsup:. I have used graphite, acetyl, glass, teflon etc as pistons and cylinders. I have got the low heat engine running with a teflon coated and polished ali cylinder and acetyl piston which works really well. Graphite pistons are better but don't last very long. I cut a few old burrettes up for cylinders as well :D.

Mark

[Spanrz]

Mark, man nice work..... I've been interested with these designs, of this type of engine.

I remember, foxtel had a program on a few months back called "Planet mechanics" I think.
2 guys went around to peoples places, making up eco-infrastructure to assist them to live by a new means.

1 of these shows, had the greenie guy make a sterling engine. He's seen them, but never made one. He guessed on a lot of "theories" when he made this huge contraption. It did work, but it just had enough momentum to work...just, there was hardly any power to use it in a functional way. No sun = wouldn't work. Funniest thing to watch, but he atleast had a go.

Same concept as your 3rd, 4th and 6th pic.

http://www1.natgeochannel.co.uk/explore/green/mechanics_prog.aspx?mediaType=video&ep=4

[TrevorW]

Actually the Stirling engine is being used to power statellites

http://www.physics.purdue.edu/outreach/INAAPT/2007/StirlingPower.pdf

[marki]

Brett there are a couple of ways to get useful power from them. The first is use a really heavy flywheel. I have see one which used a bucket as a piston and had a 5ft dia cast iron flywheel. Although it turned at about 30 rpm it could push a column of water vertically 100ft. The second way is to seal the engine to take high pressures and pump in about 5atm +. These engines really honk.

Trevor, they are/were also used in submarines to recharge the batteries whilst submerged and I believe there is also a sub that uses one to drive the screw. They were very popular before electric motors came to be and found use as a power source for dentist drills of all things. They are vitually silent in operation and just require a heat source. As usual the Germans make some crackers. My aim is eventually to build a twin like this.

http://www.youtube.com/watch?v=nE_ga5S2rhc

http://www.youtube.com/watch?v=r7kYiTohD20&feature=related

Mark

[Spanrz]

I know a guy that I used to work with, had a version of this ( http://www.youtube.com/watch?v=VIZLCOw1MVs (http://www.youtube.com/watch?v=VIZLCOw1MVs) ) but it used a Hydrogen gas flame, to power it.
Because the Hydrogen was slow burning, it sucked the flame inside where it burnt it, thus pushing the piston out.
It was a very old unit, say early 1900's type. It was initially cooled by air, but you put some water at the base of the unit to absorb some heat, to stop it seizing.

[Omaroo]

Very cool Mark :) :thumbsup:

Sterling Motors Inc. actually use this stuff for their piston/cylinder liners I believe: http://www.azom.com/news.asp?newsID=4186

[marki]

That looks very interesting Chris, I wonder when it will become commercially available? Friction is the biggest killer with these engines and machining tolerences are really tight (I have a very accurate lathe). The alcohol engine is not so critical so I was able to use a phosphorous bronze liner in a brass cylinder with an ali piston which works well as it self lubricates and oil can also be used. The cold engine is a little more exotic. When I first built it I used a graphite pistion in a glass cylinder but the graphite did not last long before the seal was lost. I ended up using and acetyl piston in ali cylinder that had been highly polised and treated with a spray on teflon coat (easily renewed) that has lasted for more than a year with little sign of wear. The other critical part is the push rod that moves the displacer. This is made of graphite rod and slides through an acetyl bearing with a good seal and stuff all friction (it will run on an ice block). The hole through the acetyl bearing is 1 size smaller then the graphite rod yet it still slides easily. It's great to watch my students try and workout what is happening, keeps them occupied for hours and really is good science.

Mark

[starlooker]

Delightful toys. :thumbsup:

[Baron von Richthofen]

I love this sort of thing, did you ever consider making a 3 or 6 cylinder radial engine:rover2:

[multiweb]

Astro-photographer AND machinist. You're hired! :lol: Jack of all trades hey ?:thumbsup:

[marki]

All the time, just have to get some time to do it :(.

Mark

[MrB]

Ditto.

Slowly expanding my collection of SIC (http://www.strictlyic.com/) magazine. Once thats done I'll get MEB (http://www.modelenginebuilder.com/). And the MEN (http://www.modelenginenews.org/) DVD.
One day I'll pick a project and do it.

[marki]

Unfortunately master of non :P.