A Tiny Reciprocator

[Ken I]

Here's a tiny engine I built based on a motor from a child's pump up toy.

It's 5.7mm bore x 5mm stroke.

It works like a two stroke - the piston opens the valve at the top of the stroke and it exhausts out the bottom of the cylinder skirt at the bottom of the stroke.

The damn thing is very fiddly - you need to get the upper volume correct for enough compressed air to drive to the end of the stroke and the valve must not leak.

(That's a US Quarter for size reference.)

I overreved it on its first run and broke the valve - so I'm going to "Plan B"

I hope I can get this to work properly before I post more detail on it.

Ken

 

[Blogwitch]

By the looks of the stroke on it Ken, it looks to be what is called a Rocking Engine, where it has a very thin piston, and at the end of it's stroke, the piston tilts and spills out the pressure.

Is this correct?


John

 

[Ken I]

John,
That's correct - the piston is effectively spherical - the odd bore size is so that I can use a 6mm OD "O" ring - which effectively changes shape with each cycle from circular to eliptical - and since its overall circumference changes slightly it also squashes up and changes in thickness etc. etc.

Is "Rocking Engine" the correct term ?

Regards,
Ken

 

[Blogwitch]

Ken,

Rocking engines on here was a bit of a craze a while back and everyone and his dog seemed to build one.

I think I made and showed mine on another site, but here is Arnold's very good build from here.

http://www.homemodelenginemachinist.com/index.php?topic=5504.0

Whether it is the same sort of engine, only you can decide, but these didn't use any o-rings, just a very thin piston solidly joined to the conrod and it 'tipped' to allow air pressure to vent out. No valving employed at all.

John

 

[Ken I]

John,
Is the crank offcentre to the cylinder somewhat to bias it - otherwise I don't see how it would work (which it clearly does).

Regards,
Ken

 

[AussieJimG]

Yes, the crank needs to be off centre. Here is a link to a transparent one that I built one morning.
It is not very flash but it works.

[ame]http://www.youtube.com/watch?v=CIdQxerZD-E[/ame]

Jim

 

[Ken I]

Thanks Jim, that makes sense - the child's toy (my grandson's) that so impressed me, definitely has a valve and "O" ring seal - but based on my experience with it, I guess I'm barking up the wrong tree.

I'll convert it to a rocker - much simpler.

Regards,
Ken

 

[Blogwitch]

Ken,

I actually found my build sequence

http://madmodder.net/index.php?topic=1492.0

And the vid

[ame]http://www.youtube.com/watch?v=YzNZ2tvEH8E[/ame]

Well worth making, and must be one of the easiest engines for a beginner to make (if just building from the plans). Just got to keep an eye on the critical dimensions.


John


John

 

[Ken I]

John,
Thanks very much for that - all the hubub on rocking engines was before I joined the forum.
I must admit its new to me - hence the reason I was intrigued enough with my grandson's toy to try to make one.

The styling of your engine is beautiful - and puts my proof of concept "brick" to shame.
When it comes to artisrty and aesthetics I have an awful lot to learn.

Regards.
Ken