Reverse Crank/Over Crank Engine

[sbwhart]

Some time ago I spotted an interesting engine at Quarry Bank Mill Style, I didn't recognise the type but after asking around I found out it was an Reverse Crank or Over Crank engine, this particular was quite small no bigger than a suite case, mounted vertically from a beam and was being used to power a small workshop. Here's a few pics of the particular engine.





The cold weather we've bin having in the UK has driven me out of the shop, so I've bin keeping myself warm in doors on domestic duties and to keep me sane I've started drawing up the engine 1/3 scale as a project to start as soon as things warm up.

I've attached some of the drawing as PDF files to give you an idea of the design, my plan is to make the engine from bar stock with the exception of the fly wheel which will be cast iron you can get these quite easily from trade, for the cylinder I'm going to fabricate this up from brass.

If things work out OK I'm planning to fit a governor to the engine, and mount it vertically on a board (painted to look like brick) with some line shafting on the back that the engine will drive, but we'll see how things work out first.

Any comment you guys have will be much appreciated.

Stew

[Rob.Wilson]

Hi Stew


Looks a great project     ,,, sure is a very interesting design   ,,,,, the cross head setup is very unusual   



When are going to start making swarf 

Rob

[sbwhart]

Hi Stew


Looks a great project     ,,, sure is a very interesting design   ,,,,, the cross head setup is very unusual   



When are going to start making swarf 

Rob

When the therms go above zero 

Stew

[Rob.Wilson]

Hi Stew


Looks a great project     ,,, sure is a very interesting design   ,,,,, the cross head setup is very unusual   



When are going to start making swarf 

Rob

When the therms go above zero 

Stew

Southern softy 



Rob 

[sbwhart]

Hi Stew


Looks a great project     ,,, sure is a very interesting design   ,,,,, the cross head setup is very unusual   



When are going to start making swarf 

Rob

When the therms go above zero 

Stew

Southern softy 



Rob 

Sorry Rob I've No Geordy Blood in me.
 


Stew

[Stilldrillin]

By 'ek Stew! 

That's a bit different....... 

Looks/ sounds a great project. Good luck, I'll be watching! 

David D

[dsquire]

Watching you lads carry on is more fun than reading the funny pages. Keep carrying on.   

Cheers 

Don

[arnoldb]

Nice going Stew; your drawings look good so far  ; I'm looking forward to the rest!

  - Arnold

  I won't mention the weather here in Windhoek...

[Rob.Wilson]

  I won't mention the weather here in Windhoek...

Yes we don't need to here how horrible the humidity is down there Arnold   ( a TRUE southern softy  )  ,,,,,,,,,,,, we have humidity too ,,, its just frozen at the moment    


Rob


Sorry for the    Stew

[sbwhart]

  I won't mention the weather here in Windhoek...

Yes we don't need to here how horrible the humidity is down there Arnold   ( a TRUE southern softy  )  ,,,,,,,,,,,, we have humidity too ,,, its just frozen at the moment    


Rob


Sorry for the    Stew

Thats no problem Rob you can't beat a good bit of blether  

I nearly posted "we bit crack" but you know how the lads across the pond can get hold of the wrong end of the stick (drug) not understanding the lingo.

 

Stew

[sbwhart]

Well more or less completed the drawings, nothing much to do but put them to the test and build the engine, I'm sure there will be mistakes in their someware I'll revise the drawing when i get the engine done. I've a few other shop type maintenace job to do first when I eventualy get into the shop.

I'm planning on fitting a governor to the engine so I've skeemed out a design for a governor to allow adjustment of the spring tension so you can vary the speed the engine runs at.

Comming to which how do you adjust the speed a governor controls an engine.

Thinks I can think of:-

Adjust the weight of the balls

Adjust the weight of the spring

Vary the ratio of drive pullies to the governor

Can you guys suggest any more ?.

I've attached a full set of drawing.

I'd welcome some cometns from you chaps

Stew

[cidrontmg]

Changing (=increasing) the weight of governor balls will not make them hang at a lower angle. In a carousel, with seats on chains, empty and occupied seats hang at the same angle. Adjusting spring tension works, so will adjusting the rotation speed.
Thanks for the plans, much appreciated!
 

[Gerhard Olivier]

That is one interesting engine  Stew

Looking forward to the rest


Gerhard

[Rob.Wilson]

Hi Stew

Looking great 

On the governor how it the pin held in place that applies pressure to the spring ?

You got any more views of the governor done   


Rob

[sbwhart]

Hi Rob

Its one of those things that I'll just have to suck it and see I may just make it a nice push fit and hope it stays put, I can always give it a dab of suppergue.

Stew

[arnoldb]

Great stuff Stew - nice set of plans  - Thank you!

I think I'll try this one scaled down to about 2/3 of your plan size - due to limited material especially for the cylinder block.  Or I might go for a fabricated block... 

Do you have a sheet with the valve chest and cylinder heads ? - not a biggy as I think I can suss it out 

 , Arnold

[sbwhart]

Hi Arnold

Thanks for your interest

Whoops I thought I'd posted the steam chest but I can see now that I havn't this should put it right

I've also attached the drawings on how I plan to fabricate the cylinder.

Just a warning if you are planning on following these drawings I had to go round the boy quite a few times to get everything fitting in place and chase the changes through, I may well have missed some, so as you build just check through that everything will fit, I was planning on revising the drawings after i do my build to get rid of any mistakes.

Cheers

Stew

[arnoldb]

Thanks Stew - much appreciated!

I'll first go through all the plans and machine each piece of the engine in my head to get a feel for it - so don't hold your breath on a quick start 

 , Arnold

[NickG]

Stew, sorry I missed this until now. Very exciting project, would love to be able to do something like what you are. I think you were spot on with all the criteria affecting governor, the only other thing I can think of is the distance between the top pin and bottom pin on arms I.e the amount of leverage the balls provide against spring. Altering this will also alter travel though.
Can't wait to see more, I've been surprised in workshop this winter, haven't felt the cold much. As Rob said, southern softie  unless it is the Geordie in us!
Nick

[sbwhart]

Thanks for you comment Nick your correct about the distance of the arm, a search of the net came up with a paper by James Clark Maxwell (a scot) written in the late 1800 its still regarded as the definitive paper on governors not an easy read, the language is a bit strange, when you get into the equations try not to understanding the maths, (I soon got lost) but concentrate on the factors  you get to understand what criteria has an effect.
 
http://en.wikipedia.org/wiki/File:On_Governors.pdf

Started doing a bit in the shop a bit of tidying and tool storage building, one or two little jobs to do that will take a week or two then I'll start on this.

But with all you guys building flame gulpers as given me    I've got a design buzzing around my head for one that I can't shake off its got a valve worked by a locomotive type linkage similar to a Walshart. 

I'm going to try a mock up of it, if its looks a goer I just may have a go at building the engine

Stew

[NickG]

Thanks Stew, will have a read of that. Your idea about the walshart type valve linkage for a flame gulper sounds intriguing too - will definitely be watching for further developments on these two.

Nick

[madjackghengis]

Changing (=increasing) the weight of governor balls will not make them hang at a lower angle. In a carousel, with seats on chains, empty and occupied seats hang at the same angle. Adjusting spring tension works, so will adjusting the rotation speed.
Thanks for the plans, much appreciated!
 

Hi Oli, I believe you are looking at it from a static perspective, when turning, the greater the mass the higher the rotational velocity necessary to reach the same height, and the spring pressure works in inverse proportion.  Once the carousel starts rotating the empty swings achieve higher heights, and thus greater distance from the rotating center and higher velocity due to the increase in radius, so the velocity difference calculated from the differing total circumferance of the path, squared, times the mass of the empty swing, will equal the lower height of the swing with a person, and thus the smaller circumferance of the circle traced, thus the lower velocity squared, times the greater mass, will equal the empty seat.  With the governor, the critical issue is to have both ends of the engine speed keeping the flyweights of the governor in the middle third of the spring pressure as that is the most linear part of the spring pressure curve, and the weight/height curve of the flyweights is a logrythmic curve, with the balls moving the most vertically relative to rotating velocity at the higher speed of the engine.  Weight of the balls must be balanced against the dynamic forces of both the spring chosen, and with consideration of the different curves as the lift of the balls is a constantly changing curve, while the spring force is close to a straight line in the midsection of it's curve, but alters substatially at either end.  In reducing the size of the engine, both an increase in natural running rpm must be accounted for, and the mass and spring factors must take into account the non-linearity of the respective curves so the governor can't be reduced by simply sizing it according to the scaling down.  I would strongly recommend some research on Kozo Hiraoka and his tables on springs and such, as he has probably the best set of tables for such I know of in the modelling world.  If I'm not mistaken, he has taken on this subject exactly in at least one of his steam locomotive books, and deals with setting up model engine governors and their weights and springs. mad jack