Introduction
Recently I made the "1 Euro 10 Micro Stirling", inspired by a Youtube video of an extreme small Stirling engine with what the maker used 2 Swiss 5 centime coins for the bottom and upper plate of the displacer cylinder.
I was quite pleased with the result but afterwards I thought it still could have been somewhat more compact and straight. In such case I never can resist in doing it over again. The result is this 1 Euro 20 cent Stirling.
Video:
The changes from the previous version:
1. I now used two 10Euro-cent coins instead of 5-cent coins. They are somewhat smaller and in my opinion the glass cylinder fits better on these 10 cent coins.
2. I could make the glass cylinder between these coins still somewhat shorter that contributes to further miniaturization.
3. I now glued the glass working cylinder directly in the upper 10-Euro cent, so the two brass rings on this cylinder could be eliminated. It is more simple, it looks better and this made it possible to decrease the total motor height for another 2mm
4. The crankshaft now has 3 round crank webs instead of the 4 rectangular web with the previous version. Tacking the webs and soldering them on the diverse axes is somewhat more easy and the crankshaft is more solid and straight.
5. The two supports for the crank shaft are identical now and both are soldered on the upper coin.
6. I made a fork on the displacer axis and on the working piston instead of the wire hooks with the former version. It looks more professional and the driving rods are turning better in it.
All in all this 1 Euro 20 Stirling is about 15% smaller than his predecessor and looks better in my humble opinion.
Running on a small tee candle light.
It should be a misunderstanding to think that such a small Stirling need very few heat to run. The power of a Stirling depends strongly to the amount of air in the system and that of course is very small here. The mechanical frictions may be somewhat smaller also but in general the ratio between the power and the friction to overcome is less favourable as the dimensions are made smaller. This for instance is the reason why a low temperature Stirling that can run on a human hand has a relative large diameter and with that a relative great air volume.
The bottom 10 Euro cent coin must be heated to about 70 degrees Celsius to let the engine run reliable. On a copper plate on top of a cup with boiled water this temperature will be reached hardy or not and the engine will not run for long in that case. So I made a stand in what a small tee candle light heats a relative thick brass plate up to about 100 degrees Celsius; see figure below.
When the Stirling is put on that preheated plate it will run almost instantly after a light push to the fly wheel; it will run as long as the candle is burning. Depending of the distance of the plate to the flame the temperature can rise so high that the Stirling starts running like a freak. In that case one better blow the flame off to prevent overheating the engine. Due to the remaining heat of the brass plate the engine will keep running for about 5 minutes which usually is more than enough for a successful demonstration.
If one wants to let the engine run constantly it can be necessary to adjust the brass plate to a higher position on the threaded part of the support. Because the flame size of the tee candle is not always the same it will be a matter of experiments to find the right height of the brass plate.
Drawing plan
For this new version I also made a CAD drawing plan and I will be glad to send it to everyone interested; click here for a request.
This drawing plan contains also a special sheet with directives for the way of working and the assembly sequence. It is more the work for tweezers than for knotty hands as I can tell you. But fun it is, for sure when you see this little thing turning on a metal plate that is heated between 70 and 100 degrees Celsius (max).
YouTube video from awJCKDup
