Monitor, A Half Trunk Vibrating Lever Back Acting Engine

[Captain Jerry]

Well I haven't cut any metal on this project yet but I have burned some midnight oil and I am getting close to a build project.  I have hesitated to talk about it because the are a few  similar builds underway and I am not going to build according to the same plans.  The plans provided by Julius De Waal are excellent, well produced, and well detailed and the many excellent models built from them are testament to their attraction.

My first introduction to the Monitor engine was Rich Carlstadt's authentic reproduction of the original engine, designed, built and installed in the USS Monitor ironclad of Civil War fame,  by John Ericsson in 1862.  To get a glimpse of what attracted me, look at :

http://www.stationarysteam.com/

I certainly don't think that I can come close to producing anything to compare with excellent example of the master model builders skill and devotion to detail.   I just want to build something that makes use of some of the unique design elements of the Erricsson engine, and is true to the design constraints of the original. 

The most obvious design factor is the twin vibrating, back-acting linkage that produced a powerful engine within the width of the Monitor's hull.   This may not have been the earliest use of this type of linkage but is certainly an advanced refinement of it.  And as far as being an eye-catching mechanism, there aren't many more attractive.

The other design feature is an Ericsson adaptation of a previous design.  The "trunk engine" was one of several designs, intended to do away with the need for a cross head guide assembly.  Rather than having a piston rod that connected to a cross head outside of the cylinder and then via a connecting rod to the crank, the trunk engine does away with the piston rod and has the connecting rod attached to the center of the piston.  The piston rod acts within a cylindrical trunk that separates the steam spaces within the cylinder from the mechanical linkage and also provides the alignment function of the cross head guides.

Ericsson's adaptation was to replace the trunk, which penetrated the cylinder heads at both ends of the engine, with a half-trunk that penetrates only the rod end cylinder head.  This allowed him to place two cylinders together, end to end, so closely that they could actually share a common head between them and be installed within the same cylinder casting.  A very short coupling that contributed to the overall width of the installation.

A third feature that is unique to this engine is a base that is painted a very nice Robin's Egg Blue, a feature that I hope to duplicate faithfully.  Here is the state of my design so far.   Note that the is nothing set in stone except the base color.

[Dave Otto]

Hi Jerry

While I have been enjoying all the Monitor projects I think this one would also be interesting to follow along with. Please continue!

Dave

[crueby]

Looks to be an interesting build! I had noticed the trunk design on the model that Carlstadt built (incredible work), and will be interested to see how you do it. Will be following along, going to need more popcorn...!

One thing on your design start - dont think the crankshaft you show will work as is, doesn't it need to be able to rotate the crank 360? The one side's connection will hit the shaft. Unless you are going to do another linkage farther back to a full crank?

What size are you thinking of for the engine?

 

[b.lindsey]

Go for it Jerry. I am sure lots of us will be following!!

Bill

[zeeprogrammer]

Oh yes I'll be watching. 

[bruedney]

I like it

I have seen pictures of the one you mentioned and thought "wow".

What drawing program are you using?

I am certainly following this build!!!

Bruce

[Captain Jerry]

Chris, thanks for taking a close look at the design.  I don't know what you may have spotted that you see as and obstruction but there may well be something out of place.  So far, there are 35 separate parts and sub-assemblies included with nearly 100 assembly constraints.  I usually don't have a problem with the first instance of a part addition, editing and fine tuning the position for best fit and smooth operation sometimes leaves a part free to move in an unexpected manner.  I was fitting the eccentrics last night and while editing their timing angle, I left the crank shaft free longitudinally.  Take a look at the .jpeg at the end of this post and see if that was the problem.

The trunk piston design has been kicking around in my head for a few years.  It represents some challenges as you can see.  My approach to a new project is to look for the one feature that I think will be the most difficult and if I cant see a way to do it, that project goes to the bottom of the list.  The trunk is that feature on this project.  My design requires a polished thin wall tube (.010") with a .400" OD x .380" ID.  Not off the shelf stuff so I have a plan.  If the plan works out, the project will begin.  If not, I'll listen to alternate plans.

Bruce, I am using an older and no longer supported version of Alibre' (V11).  Untill it craps out or I do, no need to upgrade.

Chris, Bill, Dave, Zee, and Bruce, as being the first five to respond, your front row seats are reserved.



As for size, the cylinder will be 2" OD by 3.25" long.  This is based on some material that I have on hand.  The overall width (athwart ship) will be about 8"

[vcutajar]

Nice.  Will be following along from the second row.

Vince

[Steamer5]

 

 

Jerry,
 Can I book a second row seat please? This looks like it's going to be fun to watch!

Cheers Kerrin

[bruedney]

Thanks Capt

I think I see the same issue as Chris in your first PDF

The crankshaft wouldn't turn 360 deg in that but it would in your second pic.

Thanks for the front row seat
 
Bruce

[crueby]

Yup, second pic looks fine, in the first one the crank web was between the two con rods.

Thanks for the froint row seat, looks to be a great show!

[Captain Jerry]

I went back and fixed the PDF and inserted it in the first post.  Down load the file again here if you want it.

[crueby]

One thing that I saw in Rich's engine, was that there appear to be two sets of valve eccentrics per cylinder. I've never seen that before - do you know why there are two? Is one for forward running, the other for reverse, so they did not need a stephenson link? Possible, but I dont get how the plumbing of that would work.   

Any insight on that? 

[techonehundred]

One thing that I saw in Rich's engine, was that there appear to be two sets of valve eccentrics per cylinder. I've never seen that before - do you know why there are two? Is one for forward running, the other for reverse, so they did not need a stephenson link? Possible, but I dont get how the plumbing of that would work.   

Any insight on that?

Talking to Rich Carlstadt, the second set of valves control the early steam cutoff.  As for reverse, there is an adjustable gear that reverses the direction.  You will see a handwheel on the front that controls that.   See this video @ 1:06 to see the reversal gears.
https://www.youtube.com/watch?v=VWn8gQ9Ykpk

[crueby]

Neat! I had missed that part before. Very clever linkage. Is there a name for that kind of reverse gear?