Author Topic: Muncaster's Grasshopper (Read 7092 times)

kvom · « **on:** March 21, 2018, 05:59:34 PM »

Recently Julius De Waal posted a set of plans for this engine, which to my mind would be an attractive project. Although the plans are metric, that poses no issues for CNC machines or manual machines with DROs. I would use imperial fasteners to the nearest size as I don't own metric taps and metric fasteners are less available here.

In that light, I spent the past two days starting to model the engine in Solidworks. I have encountered an issue that needs resolution before I commit to a build. The attached picture shows most of the structural components, and I am able to animate the model successfully. However the plans show a pair of swinging links connecting the end of the beam with the holes shown near the heads of the columns on the right. If i add these to the assembly, the mechanism locks into a single position. When removed and I move the crank to various positions the center distance between the two holes varies by a couple of mm out of a total length of the link of 106mm.

Some of the grasshoppers I've seen do not have the left link that attaches to the beam just to the right of the conrod. I am wondering if the two links are a variation of the Watts linkage on regular beam. That said, the Elmer grasshopper, the Eaton and Anderson, and The Potty do have both links, with both having the rocking link on the end of the much longer than on the Muncaster.

Any thoughts on the geometry issues would be appreciated.

crueby · « **Reply #1 on:** March 21, 2018, 08:03:53 PM »

I have a Stuart Turner grasshopper, the difference in the geometry between it and yours is that the link on the left has its upper pivot in the same plane as the piston rod, where yours is to the left of the rod. Try moving that over to line up with the piston.

Jasonb · « **Reply #2 on:** March 21, 2018, 08:06:01 PM »

I suppose this is the problem with third hand drawings of engines that have not been built.

Julius got them off the web and as far as I know none of his Muncaster engines have been built in metal only on the screen. Julius used the illustration from Westbury's 1957 series of articles which was only a general arrangement drawing with a few dimensions on it. Westbury based his GA on one that Muncaster did in 1934 which I have not seen and don't know if it had any more detail on it, but based on the others in Westbury's series and Muncasters original sketches in his book I doubt the 1934 one was fully detailed and may never have been built.

You can find the 1957 series on John Tom.

Jasonb · « **Reply #3 on:** March 21, 2018, 08:22:54 PM »

Might have found it.

Julius part Number, Julius dimension, Westbury dimension, julius /westbury

1-12, 90mm, 3.75", 24
2-06 102mm, 4.25, 24
2.08, 126mm, 5.125, 24.58

From this we can see that the first two links have been scaled by the same factor but the third has not. Working back using the 24 constant and westburys dimension gives the CtoC for part 2.08 of 103mm not 106mm.

Try that on your simulation and see what happens

kvom · « **Reply #4 on:** March 22, 2018, 12:25:08 AM »

I had a nice email from Julius where he explained that he's also using SW and had the same issue. His solution was to use a tangent mate between the end links with the hole a bit larger than the cross rod. So his automation worked, basically with a loose joint. He also offered to send me his SW part files, and that will save me a lot of work in recreating the entire model.

I'll give the other dimension a try tomorrow.

The fact that this engine has never been built is actually a good part of the challenge.

crueby · « **Reply #5 on:** March 22, 2018, 12:53:35 AM »

My old school double check would be a few sticks, screws, and mock it up.

JackPick · « **Reply #6 on:** March 22, 2018, 02:32:33 AM »

Quote from: Jasonb on March 21, 2018, 08:22:54 PM

Might have found it.

Julius part Number, Julius dimension, Westbury dimension, julius /westbury

1-12, 90mm, 3.75", 24
2-06 102mm, 4.25, 24
2.08, 126mm, 5.125, 24.58

From this we can see that the first two links have been scaled by the same factor but the third has not. Working back using the 24 constant and westburys dimension gives the CtoC for part 2.08 of 103mm not 106mm.

Try that on your simulation and see what happens

I think Jason meant 123mm

JULIUS · « **Reply #7 on:** March 22, 2018, 03:41:04 AM »

The calculation of JackPick is correct if you use the theory of Jason.

Julius

JULIUS · « **Reply #8 on:** March 22, 2018, 06:36:24 AM »

Grasshopper fans

I have done some more extensive calculations of the parts in question.
Part 2-08 : the center dimension will stay as 126 mm. Calculation turned out to be 125.93 mm
I have made 2 alterations.
1) Part 2-08 only one of the holes is enlarged to 7 mm round. This hole to be put onto shaft/axle/rod 2-10
2) Part 2-07.3 the hole in the bush is now reduced to reamed 6 mm round.
In my Solidworks animation this engine works fine.
I have attached the update drawing.

Julius

Jasonb · « **Reply #9 on:** March 22, 2018, 07:31:49 AM »

Won't oversize holes give a bad knock as the engine actually runs? You can't hear that on the screen

Yes meant to type 123mm which would be a constant 24mm to the inch scaling factor

You should have some sideways (arc actually) movement at the far end of the beam where you have not shown the link

Also if you want to keep it true to the Muncaster design then it should have a two part beam much like the Easton and Anderson that I built rather than a single one with it's unusual bushes that Julius has drawn.

kvom · « **Reply #10 on:** March 22, 2018, 03:46:51 PM »

From my understanding of the beam drawing in ME, Julius' model seems correct.

Jasonb · « **Reply #11 on:** March 22, 2018, 04:10:05 PM »

The reasons I said it is a twin beam are as follows.

The ME elevation which does not show anything sectioned has the top of the conrod and top of the pistion rod obscured by "the beam" which means they must both be behind it. The only way that would be true is if the beam or cylinder were offset from the engine ctr line which they are not. You can see the pump rod is infront of the beam but that is correct as the plan view shows the pumps ram offset from the engines ctr line.

The other give away are the three other unused "bosses" shown on the beam, these are the bosses for the spacers that keep the two beams apart.

You can also see that the rods all have split bearings with a means of adjustment for wear as they would on full size, pressed in bearings in the beam would never have been used on a model let alone full size. Same goes for the big end which is shown in ME as being of the marine type and totally prototypical unlike the simple pressed in bearing on Julius' version and this is the joint that has the most rotation.

kvom · « **Reply #12 on:** March 22, 2018, 04:39:43 PM »

That makes a lot of sense.

Gas_mantle · « **Reply #13 on:** March 22, 2018, 04:44:22 PM »

Is there a way I can see the fully assembled Grasshopper as I'm struggling to visualise what the extra link is that people refer to ?

Cheers

Jo · « **Reply #14 on:** March 22, 2018, 05:02:35 PM »

Don't you hate it when he is always right

Jo

Jasonb · « **Reply #15 on:** March 22, 2018, 05:12:04 PM »

Quote from: Jo on March 22, 2018, 05:02:35 PM

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 · « **Reply #16 on:** March 22, 2018, 05:12:58 PM »

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 · « **Reply #17 on:** March 22, 2018, 05:51:46 PM »

Quote from: Jasonb on March 22, 2018, 05:12:58 PM

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 · « **Reply #18 on:** March 22, 2018, 08:32:00 PM »

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 · « **Reply #19 on:** March 22, 2018, 09:29:29 PM »

Hi Jo

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

Cheers
Bruce

Jo · « **Reply #20 on:** March 23, 2018, 06:44:13 AM »

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

Quote from: bruedney on March 22, 2018, 09:29:29 PM

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

Bruce, what was on it wasn't very useful

Jo

bruedney · « **Reply #21 on:** March 23, 2018, 07:24:51 AM »

Thanks Jo

geoff5269 · « **Reply #22 on:** March 23, 2018, 12:09:37 PM »

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 · « **Reply #23 on:** March 23, 2018, 01:10:24 PM »

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 · « **Reply #24 on:** March 23, 2018, 10:46:46 PM »

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 · « **Reply #25 on:** March 24, 2018, 01:49:47 AM »

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 · « **Reply #26 on:** March 24, 2018, 07:56:18 AM »

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 · « **Reply #27 on:** April 02, 2018, 10:55:00 AM »

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 · « **Reply #28 on:** April 18, 2018, 10:50:23 PM »

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 · « **Reply #29 on:** April 18, 2018, 11:11:22 PM »

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

bruedney · « **Reply #30 on:** April 19, 2018, 05:04:09 AM »

Thanks Julius

Jasonb · « **Reply #31 on:** April 19, 2018, 07:04:50 AM »

Thanks Julius, I do think it looks nicer with the twin beam and the slim rods between rather than the forked ends.

kvom · « **Reply #32 on:** April 24, 2018, 03:22:28 PM »

In examining the Solidworks parts I noticed that the cylinder is larger on the new version than the old. I emailed Julius about this, and he replied that the split beam version is 1.5x larger than the previous. That means that the cylinder is 218mm or 8.5" long. I think building to this size would be a challenge for most. My plan is to build the engine, but I believe I'll use the V1 model plus the V2 beam that I'll scale back.

The V1 cylinder is 130mm or 5.11", still a challenge. If I can find appropriate size hydraulic cylinder tube with a honed ID I'll use that. Bore is 45mm (1.75"), but I suspect that's larger than is really needed.

Jasonb · « **Reply #33 on:** April 24, 2018, 04:18:31 PM »

Or you could convert the metric into imperial using 1mm = 1/32" which will bring the sizes down closer to the original. Scale the cad drawing by 0.79365 to get the same result

kvom · « **Reply #34 on:** April 24, 2018, 05:50:12 PM »

Both my CNC mill and th manual machine DROs support metric measurements, so I'm going to try to stick to metric dimensions except for fasteners and their holes.

bruedney · « **Reply #35 on:** April 25, 2018, 01:14:31 AM »

Hi

Just started redrawing using Julius' latest version but, like kvom, I am scaling it down by half where I can

Julius, I have found a few issues so far with some things missing as below.
1. There is no end part for the base that is under 1-01.4.
2. There is also no holes for fastening said piece to 1-01.1

These are not critical - Just thought you would want to know

Thanks again for these awesome works of art

Cheers
Bruce

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Author Topic: Muncaster's Grasshopper (Read 7092 times)