Mumford link... how you do that?

I've been reading up on rear suspension design and I'm more than enamored by the Mumford Link. But I can't find anything that describes how you actually design it. I mean, how do you figure the lengths and pivot points? I can pretty well figure out how you want to place the two main sections to determine the roll center, but it seems like the rest is pretty critical to get exactly right or it will bind. Anyone have any info?

Thanks,

Ed

Is that like where you play the guitar and drum at the same time?

http://www.youtube.com/watch?v=lLJf9qJHR3E

Can't give you specifics except to say a lot of UK clubman racers (like the Mallock U2) use this system (typically with a Spridget-based rear axle). Maybe look up info on Mallock?

Here's SOME INFO

Amazing, I'd never seen one before

Didn't Andy have one on the second incarnation of the Fiat?

There are a lot of them out there. When I google, I find lots of info on how they work and loads of pictures of them, but nothing about how to actually design one. Weird.

looks like a very elegant design.

Anybody ever seen/felt on in use?

Ask, and locostusa.com shall provide:

http://www.locostusa.com/forums/viewtopic.php?t=77

In reply to RossD:

Ah, thanks. Good info there. The guy who built one seemed to confirm some things I assumed from looking at the pictures - the points being horizontal. So if you look at the two main arms, and extend them until they meet, that's kind of the constant length. Okay, you make one side shorter. Call the amount you made it shorter by "X". Make a link that is X long that rotates at it's center. Bingo- that center will give you the horizontal point for the other points. Then the middle link is just vertical, which determines where that center point actually lands. So the other sides main link is the same as the first side, and the points for the bell crank are all determined by points you've now found.

Well. I know what I meant. Not sure that made any sense.

I'm not sure how to turn that into math, but I could lay it out. I like the idea of doing it in cardboard and using tacks for the pivot points so you can move it. Would be neat to play with too.

Thanks!

In reply to mad_machine:

I have seen one, but not driven or ridden in a car that had one. I know a guy who I could pay to make it and he would do it like artwork. But my last welding project actually turned out okay and I'd really like to figure it out and build it for myself- or at least take a crack at it before I bring in the pros.

http://texaslocost.homestead.com/Mumforddrawing.html

Did you see this link at the end of the thread?

In reply to RossD:

Oh, will you look at that. I've seen what look like two types- the ones with a vertical middle link and what that drawing seems to come up with. Seems if you get a center section worked out you can just modify the two side links to position the roll center where you want it. So that could be the whole answer right there.

Thanks a ton!

Mumford... interesting... thanks OP for showing me something new.

it just seems like it could be a good alternative to the panhard rod that Fiat used on the 124

Question: why not put the mumford link's rods and pivot mounts up above the axle instead of hanging down below? Seems like you would get more ground clearance and I can't think of any disadvantage.

In reply to just_james:

The whole point of a Mumford Link or WOB link or any other panhard rod alternative is to get the naturally high roll center of a stick axle down lower. mounting the Mumford bits upside down would have the opposite effect.

Am I missing something, or does the mumford link pictured have no provisions for roll?

Maybe it's my mushy brain from too much studying.

This page has a cad sheet in pdf that shows how the roll center is calculated for a mumford.

http://www.lescanfield.info/rear_geometry.htm

Wow it's like two watt links conected. Strange!!!!! Wonder why it was developed? What was in the way that made it this way?

Well, I really had a thorn in my side about not really understanding it, so I threw together a model and took a video of it's motion. I figured I'd post it up for you guys. It helped me understand it, and it may help you too.

http://www.youtube.com/watch?v=zBapgVQlzLA

If the link doesn't work give it a minute, I just uploaded it.

Taiden wrote: Well, I really had a thorn in my side about not really understanding it, so I threw together a model and took a video of it's motion. I figured I'd post it up for you guys. It helped me understand it, and it may help you too. http://www.youtube.com/watch?v=zBapgVQlzLA If the link doesn't work give it a minute, I just uploaded it.

Very good! Thanks!

In reply to Taiden:

what did you model this in?

I emailed you back. Student version of solidworks. (Like killing a mosquito with a nuclear bomb) If you find anything free that is just a simple geometry program let me know!

I can barely understands a watts link, brain is now fried

Hmmm, you know, it's not so hard to mount a Watt's link with the bellcrank on the chassis and links out to the end of each axle.
Or, to lay it down horizontal instead of vertical.
Of course, like any suspension, you need to take care with the mounting points to preserve the geometry.
Take a good look sometime at the Watt's link used on rear of PT Cruiser.
The bellcrank is asymmetrical, and the links are different sizes.
But critical proportions are maintained, so it works (remember 'similar triangles' from High School Geometry?).