Robinson Hot Air Engine

[Trevor]

HI all
I am in the process of making a Robinson Sterling engine with a piston diameter of 39mm and a stroke of 34mm giving me a 40.6CC volume.
My displacer cylinder is 69mm internal diameter (stainless Steel). With a ratio of approx 1.6:1 the displacer cylinder has a stroke of 18mm which isn't much and I am restricted to this sizing.
So! What I need help with is can I make a longer displacer cylinder and displacer piston with such a small stroke of the displacer piston without losing the the normal 1/3rd - 2/3rd recommended ratio. Will the longer displacer I am thinking of using cause to much heat loss when the displacer piston is too long.
Trev

[Ian S C]

With the Robinson the displacer is short and fat, and in full size has an internal regenerator. At a glance I would say that you are going in the right direction.

Here's a photo of a mates Robinson a the local A&P Show the day after it arrived in New Zealand from Australia.

Ian S C

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[Trevor]

Thanks Ian.
Nice looking engines and I hope mine will look something of the same. I used a small milling machine from a neighbour to make a water channel through the top section and I might as well make a small water cooler on the bottom as well.
After a lot of thought, I will go with an internal regenerator made from stainless kitchen scourers.
I have managed to finish the drive network and now comes the hard part.
Thanks again - Trev

[Ian S C]

Qn the full size motor the vertical rectangle between the crank and the flywheel is the water tank. The piston on the motor in the photo is 10" dia, and the axe is to chop the wood for the fire, the owner didn't have any fire wood at home, so he got some bags of fire wood at the petrol station on his way to the show.

[Trevor]

Pretty awesome. Certainly would be nice to have one of those.
I made up the displacer and the regenerator and finally got it all together today. I ended up with a 20mm depth displacer and a 20mm stroke.
Fired it up and away she went. Pretty good watching the linkage work. I will set up some pics after I have painted it and made a fire box for it.
Trev

[Ian S C]

Trev, it's a good feeling when you get a motor that you built your self going.

I build my motors to be developed, so I don't do much painting, usually just the flywheel. Have known people that have got their motor going, then stripped it down and painted it, then had trouble getting it going again.
Ian S C

[Trevor]

Know that feeling Ian (hee hee). Here are some pictures of the finished parts I did. I still need to finish the meths burner and fire box proper.
Had to borrow a milling machine from my mate to make water channels in the main block and then screw on a top plate, Whew!!! That was a chore and many screws.
My engines go on display at the Cairns Show with my cousin Ted who has steam engines - Makes for quite a display when they are all running.
I very rarely make any changes to them except maybe to pretty them up. Love your work though Ian.
Trev

[Trevor]

The Pictures as finished articles
Trev

[Ian S C]

It seems that there are a few 'model engineers" in the Cairns area, there is a couple on the Model Engineer web site, Hopper, and Brian, the former an experienced modeler, and the latter a newby.

My second motor used a sewing machine wheel for many years until I needed it for another motor, so I made a new one for the old machine, a bit heavier which helped a bit with the power, the motor will actually work at high speed and virtually no torque with no flywheel at all, but set up right it can make it to 5 Watts. That motor is based on Dyna by James G. Rizzo in vol 1 of the "Stirling Engine Manual".

Ian S C

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[Trevor]

That's quite a beautiful engine you have made Ian and I do like the radiator. I have just recently brought a computer radiator which suits a small fan and I will be looking forward to using it on a small power house like the one you have built.
I must try and contact the two modelers you have mentioned. You seem to be pretty good with your memory, mines shot (heehee).
Thanks Ian
Trev

[Trevor]

Yep! Should have listened to you Ian - Painted it, and guess what! It would not go no matter how hard I tried , however I eventually got it finished and operating correctly.
Certainly isn't any horse power here, but it does run realistically - didn't need to add water to the cooling as it run for an half hour. If you look at the large version with it's 10" power cylinder and only 1/3 HP, it is a wonder the little models work at all.
Here is a couple of pics of the finished product.....

[Ian S C]

Little hot air motors aren't quite useless, here is my ALPHA motor, 20 mm stroke x 30 mm bore, free running max revs 1800 rpm, best working speed 600 rpm - 800 rpm, and here it has a mini power hacksaw, that with a new blade, and a bit of luck it will cut through a bit of 10 mm rebar (steel) in about 20 minutes. The blade is an Eclipse Junior Hacksaw blade. Sorry no video.

Ian S C

[Trevor]

Nice one Ian - I made a few changes to the motor and also removed the door. It is now fitted with a water pump and runs extremely well.
One good thing it runs at a realistic slow speed and the water cooling works quite well as the only cooling the engine has is the top plate. Here's a pic of it with its trimmings.
Trev

[Trevor]

The pic shows the water pump and gearing for same. I originally had problems with the heater with so much back heat onto the burner and wood work I had to change it dramatically.

[cbstirling2]

Trevor, well done!

PM Research sells some powerful "toy" Stirling engines.

I have a a couple of theirs and both can run toy Mamod workshops.