Muncaster's Grasshopper

[Jasonb]

Don't you hate it when he is always right   

Jo

Thanks for that Jo though I did not spot that the end pivot is cross braced

They are a lot clearer than the ones in the Westbury series too. The most useful part is having the dimensions of the "beam" which should make it easier to plot the correct geometry so the engine works without having to resort to putting a 6mm pin in a 7mm hole

If you do try and plot it out the side elevation also shows the vertical post 13/16" from cylinder ctr line which if using the 24mm/1" would be 19.5mm not 20mm as drawn

[Jasonb]

Peter have a look at this which gives more of Julius' drawings including some of his version assembled

http://modelengineeringwebsite.com/Muncaster_grasshopper.html

[Gas_mantle]

Peter have a look at this which gives more of Julius' drawings including some of his version assembled

http://modelengineeringwebsite.com/Muncaster_grasshopper.html

Thanks, I can see what you are talking about now 

[JULIUS]

Jo
Thank you for posting the additional drawings of the grasshopper.
The only drawing I had was the page with figure 1 and figure 2.
I might now revisit the grasshopper engine and produce a set of drawings with a split beam.
Again thank you.

Julius

[bruedney]

Hi Jo

Thanks for those scans of the 1934 article. Don't suppose you could add page 467 could you?

Cheers
Bruce

[Jo]

Julius: if you revisit it please do not delete your original design  that way builders can choose from building a single beam or dual beam version 

Don't suppose you could add page 467 could you?

Bruce, what was on it wasn't very useful 

Jo

[bruedney]

Thanks Jo 

[geoff5269]

When I was building my grasshopper I noticed that the links were half the length of the beam pivots and when the beam was level the piston rod and pivot ends and beam end all lined up, and this is what you had to aim for.
Geoff

[Jasonb]

There are a  few different options for the links on Grasshopper engines and they don't all have the link pivot on the cylinder ctr line. Provided all the parts are correctly sized they will work Ok, Elmers #37 grasshopper is just one example where the link is offset from the cylinder as we see in the Muncaster, actually quite a bit more offset.

[kvom]

This build will have a few challenges.  The cylinder bore is 130x45mm (~5x1.75"), so quite deep.  Milling the corresponding concave surface for the port block will take some care to get a good fit.  The top and bottom flanges will be turned separately since the collar that supporte the stationary vertical stays wraps. around the cylinder more than half way.

The flywheel is 9.5mm thick and 269 mm in diameter.  I'd like to find a casting, but one that thin is difficult.  It seems likely that I'd just buy one of Martin's 10.5" wheels.

[kvom]

As a Solidworks relative beginner I have to say that examining the parts Julius sent me is quite an education.  I learned several new things just from the bevel gear.

[Jasonb]

You might want to think about finding an off cut of hydraulic tube which will have a finished bore and use that for the cylinder. If not it shouldn't be too hard to turn I have done several cylinder liners that are longer than that and if you use cast iron you won't have to make the external shell and sleeve which will half the work, brass or bronze one piece would also be an option but a bit more costly.

I suppose you will do the curve using the CNC but it is also quite easy to do with a between ctrs boring bar in the lathe, this one is 80mm long and similar diameter

[Gerry]

Don't know if this is common knowledge or not, but I have attached a couple of pictures showing a method of working out the geometry of a grasshopper beam and the dimensions applied to JDWs drawings. This gives a straight line within ~ 0.05mm for the piston rod without excessive clearances.

Gerry

[JULIUS]

Modelers

After Jo placed the drawings of the Grasshopper on this site I had a look at the drawings and had a better understanding of the engine as shown on the drawings.
I have produced a set of drawings which reflects basically the engine as per drawings posted by Jo.
There are some differences and have tried to design it so that standard bar stock can be used and hopefully castings can be dispense with.
I hope the drawings are clear.

Julius

[kvom]

Can you email me the new set of solidworks files please?