Author Topic: Roy Ozouf's Coventry  (Read 20098 times)

Offline kvom

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Roy Ozouf's Coventry
« on: April 29, 2015, 06:18:59 PM »
I saw this engine running at NAMES, and was able to locate the source for plans.  It's a booklet that's sold on EBay titled "Three Elegant Oscillators", published by Cammelback Press.

Here's a video of it running:


The name Coventry relates to an Englishman, Don Coventry, who found a similar engine in a surplus store and published a picture in Model Engineer.  It's unusual for having the pivot at the bottom of the cylinder rather than at the center, as is the case with the McOnie.

Since NAMES, I received the booklet with the plans and have been modeling it in Solidworks for the past few weeks.  The parts are all numbered neatly and total 66 unique ones.  Obviously a few need multiples.  I found only one minor issue with the drawings, which are all in imperial dimensions.  The flywheel is 5.25" in diameter, to give an idea of its size.  The following are renderings which show how the engine is built:

I ordered a flywheel casting from Martin's Models, and the rest will be built from bar stock once time allows.

« Last Edit: April 29, 2015, 06:22:05 PM by kvom »

Offline sshire

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Re: Roy Ozouf's Coventry
« Reply #1 on: April 30, 2015, 11:45:05 AM »
OK. You're definitely ahead of me.  :ROFL:
I've been looking at the plans on and off and they are nicely done.
It will be next in line after the PMR horse vertical. I'm still kicking around the idea of modeling the frame, 3D printing it twice  and having Cattail do a set of castings.
Best,
Stan

Offline jeff l

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Re: Roy Ozouf's Coventry
« Reply #2 on: April 30, 2015, 01:54:50 PM »
I think that this engine was featured in MODELTECH  many years ago , Roy included his method on machining the frames from solid stock using a fixture plate on a rotary table .Jeff

Offline tvoght

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Re: Roy Ozouf's Coventry
« Reply #3 on: April 30, 2015, 02:10:55 PM »
I received the book yesterday. It appears the book is a reprint of the Modeltech article Jeff mentioned (and two others). It's a nice set of plans. The engine was high on my list, but while waiting for the book, a couple more engines have creeped onto the drawing board. Now the list is being reshuffled -again-. Sigh.

--Tim

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #4 on: April 30, 2015, 02:23:21 PM »
Since several have received the book, I'll mention the problem I found with the plans.

On the valve block, the exhaust channel passes too close to the bottom steam port.  Easiest solution is to make that port less wide and the exhaust port wider.

Solidworks says frame volume is 78.17 cubic centimeters.  STL loaded to Shapeways says 78.28.
« Last Edit: April 30, 2015, 02:39:17 PM by kvom »

Offline Jasonb

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Re: Roy Ozouf's Coventry
« Reply #5 on: May 01, 2015, 08:05:17 AM »
I'll be following this one along but wondered if as both of you are going for "mass" production of the frames either by CNC or casting that you may want to consider this :LittleDevil:



« Last Edit: May 01, 2015, 08:19:26 AM by Jasonb »

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #6 on: May 01, 2015, 01:00:46 PM »
Very cool.  Thanks for posting, Jason.

I am going to CNC the frames, but it's unlikely I'll do more than 2 of them.  :ShakeHead:

Offline sshire

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Re: Roy Ozouf's Coventry
« Reply #7 on: May 01, 2015, 05:36:18 PM »
That's great. Thanks, Jason.
It's not the frames. It's making 3X the number of parts.  :ROFL:
Best,
Stan

Offline Jasonb

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Re: Roy Ozouf's Coventry
« Reply #8 on: May 01, 2015, 07:54:25 PM »
Well you should get them right by the third time of trying :mischief:

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #9 on: May 08, 2015, 04:42:37 PM »
Some thinking about the valving led to the following reasoning:

1)  The pivot rod and crank are positioned vertically relative to each other, so that at TDC and BDC the cylinder will also be vertical.

2) The link needs to be 180 degrees out of phase so that when the piston is at the top the valve is at the bottom.  Therefore the eccentric needs to be placed on the crank with its throw opposite to the crank throw.

Then to verify the valve motion I drew up the attached in Draftsight using the eccentric throw of .109 and the two lever arm lengths of 1/2 and 11/16.  This shows that the valve will move .15" from its center position.  The length of the valve is .55, so that when it move .15" the edge of the valve exactly exposes the steam port.  QED.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #10 on: May 08, 2015, 04:49:55 PM »
And thinking about that triple cylinder version, it looks as if each cylinder must exhaust directly, with the pivot rod having only the air supply passage.

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #11 on: May 18, 2015, 09:25:30 PM »
I received the flywheel from Martin today.  Looks really nice.  Must leave it alone until the other engine parts are completed.  In any case I have a setup on the mill that I can't tear down yet.

Offline sshire

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Re: Roy Ozouf's Coventry
« Reply #12 on: May 18, 2015, 10:45:43 PM »
Big thumbs-up for Gary Martin's flywheels. They're cast very well and machine beautifully.
Best,
Stan

Offline kvom

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Re: Roy Ozouf's Coventry
« Reply #13 on: October 22, 2016, 12:05:57 AM »
Only 17 months since my last post, during which time Stan has already built his.  After a couple of months of doing nothing in the shop, I decided to actually make a start.  My first parts are the two crank shaft spacers and the crankshaft side shafts.  My veterans copy of Solidworks expired, and until I get the 2017 version I can't generate any DXFs from the model.  So mostly I'll be doing manual lathe parts for a while.

A friend of mine is building a large CNC plasma table, and as an experiment I'm going to cut the frames using it.  Supposedly it's accurate to a couple of thou, and the software takes into account the width of the kerf.  I'll probably draw it with 15 thou roughing clearance and finish machine on my mill. 

Offline philjoe5

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Re: Roy Ozouf's Coventry
« Reply #14 on: October 22, 2016, 04:11:44 AM »
Thanks for this link:

http://www.ebay.com/itm/Build-Roy-Ozoufs-classic-THREE-ELEGANT-OSCILLATORS-model-steam-or-air-engines-/6011011919

I will be following this build.    Definitely an engine on the bucket list.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain