# Coomber Engine Ideas



## vederstein (May 3, 2020)

On to my next engine.

I was looking at Elmer's #46.  The Coomber engine.  (I don't know if it's "Coomber" or "Comber".  I've seen it spelled both ways.)

Anyway, these designs always have the cam ring with the cam rollers on the inside.  I was thinking what would happen if I put the cam rollers on the outside:

1. The cam would be easier to make with manual equipment.  It would like machining a large cam profile for a gas engine.
2. The cam would be overall smaller because the rollers are on the outside and not the inside, making for a smaller part.

So I proceeded to do some conceptual design work to just flesh out the idea a bit.

At this stage I like that the elliptical shape of the cam is more accentuated from a circle and its shape can be more identified as not circular.

Here's a short video of the idea.

(As usual, if this engine goes to completion, I'll post the design files on this forum.)

What do you all think?


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## vederstein (May 10, 2020)

A bit more design work and it ideas are coming together....


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## johnmcc69 (May 10, 2020)

Looks good Ved! I'm looking forward to seeing how you do the valving.

 John


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## vederstein (May 11, 2020)

johnmcc69 said:


> I'm looking forward to seeing how you do the valving.



The bronze bearing on the axle has two 1/8" wide slots along the perimeter.  It's a similar setup to a wobbler's  radial slots except the slots are on the circumference pointed to the center axis instead of curved slot around the center of rotation.

When I get around to finishing the prototype, I'll post the drawings and it'll make sense.

Externally, it won't look much different though.  All valving is internal.

Thanks for the inquiry.

...Ved.


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## awake (May 11, 2020)

Very interesting!


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## vederstein (May 17, 2020)

I believe I've worked out the final issues.

I've modified the base, removing the undercut, thus making is sand castable.  I added fasteners and adjusted a couple of items that didn't work out.  So I'm off to creating the first set of drawings.

From these drawings, I'll make the first one.  If all works out, I'll post the design.


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## johnmcc69 (May 17, 2020)

Will you have to make any provision to stop the piston rod from turning on its axis?

 John


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## vederstein (May 17, 2020)

Nope.  If there is an issue and the rod rotates, I can add a flange to the cam rollers.


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## Peter Twissell (May 18, 2020)

I can guarantee that the rod will rotate. Contact between the rollers and the cam is not normal to the rod axis (except at TDC/BDC), so it will exert a moment about that axis.


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## vederstein (Sep 13, 2020)

I've managed to get my inverted Coomber prototype running.  It's not particularly pretty, but it does run. Here's the final design.








First the design assembly files:


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## vederstein (Sep 13, 2020)

Now for the part drawings:


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## vederstein (Sep 13, 2020)

The 3D solid model and casting patterns for the Inverted Coomber engine:


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## ICEpeter (Sep 13, 2020)

vederstein said:


> I've managed to get my inverted Coomber prototype running.  It's not particularly pretty, but it does run. Here's the final design.
> 
> 
> 
> ...




Hello Vederstein,
What is that pretty antique car in the background of your photo? An Austin or MG or what else could it be?

Peter J.


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## vederstein (Sep 13, 2020)

1952 MG TD

Ive had it about three months now.  It's my "unicorn."


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## ICEpeter (Sep 13, 2020)

vederstein said:


> 1952 MG TD
> 
> Ive had it about three months now.  It's my "unicorn."



My first car was a 1958 MGA, a lovely car that  I drove for a number of years - never mind the leaks and draft through the soft top and inadequate side windows. Wish I still had it!

Peter J.


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## Anatol (Sep 14, 2020)

Peter Twissell said:


> I can guarantee that the rod will rotate. Contact between the rollers and the cam is not normal to the rod axis (except at TDC/BDC), so it will exert a moment about that axis.


surely, IIUC  the rotating piston rod and cylinder would be a feature not a bug - like precessing valves, preventing wear asymmetries in cylinder wall...?


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## Anatol (Sep 14, 2020)

vederstein said:


> I've managed to get my inverted Coomber prototype running.  It's not particularly pretty, but it does run. Here's the final design.



fascinating. The valve system remains a mystery, I'm assuming its a wobbler style, but rotary - very simple. How are you sealing ?
Also, is there a good reason for the overhung cam-rollers? A clevis style would be more balanced, no?


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## vederstein (Sep 14, 2020)

Sealing?!?!?!  This thing leaks all over the place.  It was more important to have it freewheeling than well sealed.  It doesn't have a lot of power, so it cannot have much drag.  I'm sure the design can be improved, but it's a first of its kind.


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## Anatol (Sep 14, 2020)

To be clear, I think its a really interesting topology especially because of the reduced moving parts count.
Are you saying that the mechanism, in your opinion, is a novelty that would be unlikely to have practical use?


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## LethalLeigh (Sep 14, 2020)

Beautiful MG Vederstein


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## vederstein (Sep 14, 2020)

In the 1800s the Coomber was a real engine, but there is a reason why it doesn't exist anymore.  So yeah, at this time it's a novelty.


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## Peter Twissell (Sep 15, 2020)

Anatol, rotating pistons and valves are fine for wear distribution, but this engine has a roller on each end of the rod which must remain aligned to the guide wheel.


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## davidyat (Oct 25, 2020)

*I finally finished my "problem child" Coomber. I followed Vederstein's plans. All through this build, I was encountering small "teething" problems, mostly because I didn't follow instructions!!! When I assembled all the finished parts, it would rotate very freely with no air. Introduce air and all kinds of binding problems. Got them fixed. Took it all apart, painted everything and reassembled. Again binding problems with air. Finally fixed it and finally got it to run under power. It's probably going to be the only time it runs under its own power as I'm not going through this again. Now it looks great on my bookcase shelf. I've included 2 videos, one running before painting and one after.
Grasshopper
*


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## vederstein (Oct 25, 2020)

Good job David!


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