# Rhombic drive hot-air engine



## gunna (Feb 12, 2011)

In my Welcome post I mentioned a hot-air engine I had made. Here are some pictures. The diagram shows the fundamental operation with the displacer shaft (con-rod?) passing through the centre of the power piston. The four small arms that form the rhombic drive have 3/8 x 1/8 ball bearings in each end, 8 in total. The two crank shafts are geared together and also run in ball bearings. The gears came from a dead battery drill and are very noisy, the displacer piston is made from the thin wall stainless tubing used in solar garden lights with brazed in plugs each end, while the power piston is cast iron. It runs at a little over 1000 rpm with the little meths burner.
Ian.


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## compspecial (Feb 12, 2011)

Great job, Ian must be fascinating to watch the motion, where did you source the ball-bearings from? 
                       Stew.


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## gunna (Feb 12, 2011)

compspecial  said:
			
		

> Great job, Ian must be fascinating to watch the motion, where did you source the ball-bearings from?
> Stew.


Thanks Stew, the bearings came via my local "full size" bearing supplier. He had to do a bit of a catalogue search but finally decided he was able to get them. Only took about a week from memory. If you have enough old computer fans, they are the same ones usually.


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## dnp101677 (Feb 19, 2011)

Nice job! 

I really like this engine; it is very interesting. Where would one find plans for such a design? I remember seeing something like this in my travels thoughout the ciber space, but I don't have anything in my collection of plans. 

I'd love to see a video of your engine running if you have one.


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## DougLanum (Feb 19, 2011)

Here is an 11cc Rhombic drive engine made from an article in Model Engineer Magazine. It turns at 3000+ RPM.


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## gunna (Feb 20, 2011)

dnp101677  said:
			
		

> Nice job!
> 
> I really like this engine; it is very interesting. Where would one find plans for such a design? I remember seeing something like this in my travels thoughout the ciber space, but I don't have anything in my collection of plans.


Hi dnp, this one came from Model Engineer mag starting in 30 September 2005.
Ian


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