Putting my new Creality printer to good use I have designed this simple engine and it runs really well.
It is the printed version of my previous design. https://youtu.be/5_50RuMcc28 If you don't have a printer you could try this one.
The STL print files are here https://www.thingiverse.com/thing:2510395
Assembly video
Other links
Creality 3D® 3D printer: https://goo.gl/wXrkMi
Discount code 20%off for CR -10 3D printer: bg3dprinter
Foam cutting tool https://goo.gl/GLmi10
MF63ZZ Flange Ball Bearings: https://goo.gl/KQC4G8
Drill bits collection with discount: https://goo.gl/Rp4WaM
15%off for drill bits: BGDB15
Drill bits collection with discount: https://goo.gl/Rp4WaM
15%off for drill bits: BGDB15
YouTube video https://youtu.be/ri_xSrEnjDY
Notes
With my other designs that used the travel sweet tins I got a lot of comments that people could not get the tins in their country.
The outside diameter of the tin lid is 98.7 mm. If you have something fairly close it could still be used. You would need to scale the print for the cylinder, frame and base ring to fit. The other parts can be printed as supplied.
The displacer diameter would also need changing to suit your tin. It should be made so there is a gap of 2-3 mm all around it.
You may have to open out the holes in the prints a little to fit the bearings and frame and base together, it depends how good your printer is.
If you have no metal rod for the crankshaft and crankpins you may be able to find some nails the right diameter. Ebay sellers have brass and steel in short lengths.
If you have no metal rod for the crankshaft and crankpins you may be able to find some nails the right diameter. Ebay sellers have brass and steel in short lengths.
A low power engine like this has to have very little friction to work.
The needle and pencil top fit is critical. The displacer must be able to fall under it's own weight but be as airtight as possible. Get a packet of assorted needles and select the best size.
The diaphragm must be loose like shown in the video. If you don't get very long runs try another diaphragm and don't forget the WD40 which makes the latex more pliable.
My engine will run for around 30 minuets on a cup of hot water. I got 90 minuets when it was placed on a thermos flask. You could get longer runs by insulating the flask and the exposed part of the engine's bottom plate.
The cranks are set 90 degrees apart. You can try varying this a little to get the best performance.
I made 2 engines, The second for the video. There was a week between printing the parts and assembly on the second one and I found the diaphragm ring had shrunk a bit and would not fit although it did when first printed.
I would suggest then if there is to be a delay before printing and assembly that the ring is fitted to the base with a bit of glove between to hold it's size.
I made 2 engines, The second for the video. There was a week between printing the parts and assembly on the second one and I found the diaphragm ring had shrunk a bit and would not fit although it did when first printed.
I would suggest then if there is to be a delay before printing and assembly that the ring is fitted to the base with a bit of glove between to hold it's size.
Any questions you can ask here or on the Youtube video comments.
I moderate comments here to prevent spam so if you leave a comment you may not see it straight away but I will.
How it Works
The principle of the Hot Air or Stirling Cycle engine is not well known. It is difficult to see how it can work just by applying heat.
If we take an empty can and stretch a piece of balloon over the top, like the diaphragm on our engine, the air is sealed inside.
Apply heat to the bottom of the can and the pressure inside the can will rise and cause the balloon to rise a little.
Now if the bottom of the can is cooled by placing it in a dish of water, the air inside will cool and the pressure will fall. The balloon will be sucked inwards.
So to get our diaphragm, which is a simple form of piston, to drive our engine all we have to do is alternately heat and cool the can.
This is not very practical but the same effect can be achieved by heating one end of the cylinder, the bottom, and the moving the air inside alternately from top to bottom. This is the function of the displacer.
The displacer takes up space inside the cylinder, when it’s at the top, all the air inside is displaced to the bottom where it is heated and expands.
When the displacer is at the bottom of its stroke, the air is moved to the top, which has a cooler surface, and it contracts.
Remember, the displacer does not touch the sides of the cylinder. It is not a piston. As it rises and falls air passes around it as it is transferred from top to bottom. It’s the same air that is continually heated and cooled.
For the engine to work the top has to be cooler than the bottom.
The larger the temperature difference we can get, the more powerful the engine will be.
The configuration of the cranks and connecting rods allow the displacer to move in the correct relationship to the diaphragm and flywheel.
When you have your finished engine in front of you, it will be easier to understand the principle.
Animation supplied by Draco.
