ian.stewart
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| posted on 27/5/16 at 08:28 AM |
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Watts Linkage, Thoughts Please
Im still building my little special, and, because it is so little packaging of the rear suspension is being somewhat challenging, I need to locate
the rear suspension a bit better than the 1/4 eliptics offer.
Ideally I would put a watts linkage thru the centerline of the dif, but the fuel tank sits far to close to the axle to allow the link to fit, nor is
there space for a panhard link to work effectively without causing body jack. so, my thoughts have gone back to the watts linkage, but mounting it in
a different plain, If I mount the pivot pin on the bottom of the diff, and mount the rocker arm in a spherical bearing, so making the watts link run
under the diff, obviously all will fit within the scrub radius, and only protruding perhaps 30mm lower than the diff casing, I dont see this causing
any problems, and, might if im thinking correctly probably lowers the roll centre too?
Something different, Very different..............
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nick205
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| posted on 27/5/16 at 08:37 AM |
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I think I follow your description, but a sketch if you can may help others understand it and comment on it.
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Slimy38
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| posted on 27/5/16 at 08:41 AM |
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Do you mean something like this;
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ian.stewart
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| posted on 27/5/16 at 09:01 AM |
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quote:
Originally posted by Slimy38
Do you mean something like this;
Yep exactly like that  Obviously my brain is not as addled a I suspected
Something different, Very different..............
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nick205
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| posted on 27/5/16 at 09:15 AM |
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Yup, that's exactly what I meant and really helps illustrate what you have in mind.
Having something lower than the bottom of the diff runs a risk of being bashed, but TBH if you bash something like that you're likely to be off
road in it.
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sprintB+
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| posted on 27/5/16 at 10:32 AM |
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There is another linkage which some say is far superior to Watts, its called the Mumford set up, I have drawings and pictures but cant fathom how to
upload yet. I use it on my Dutton and it seems OK but have nothing to compare it with.
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johnH20
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| posted on 27/5/16 at 10:51 AM |
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The Mumford link was used on U2 Clubmans cars if I recall, supposedly to lower the roll centre compared with a conventional Watts linkage. I suspect
it would have the same package problems as the latter have for you.
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Sam_68
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| posted on 27/5/16 at 11:53 AM |
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quote:
Originally posted by sprintB+
There is another linkage which some say is far superior to Watts, its called the Mumford set up, I have drawings and pictures but cant fathom how to
upload yet. I use it on my Dutton and it seems OK but have nothing to compare it with.
Mumford link:
No good to the OP, though: the objective is to give a lower rear roll centre when used in the 'normal' orientation as shown. It
you're rotating it through 90 degrees to lay it flat, as suggested, then that becomes irrelevant, so it would simply be a more complicated
solution for no advantage.
Thinking out loud, but a WOBlink might be an interesting possibility: turned through 90 degrees to lay flat and pivot 'C' mounted to the
underside of the diff., it would give you the opportunity to mount both chassis pickups ahead of the axle and off to one side, making it easy to fix
them to the cockpit rear bulkhead with minimal chassis structure behind?:
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ian.stewart
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| posted on 27/5/16 at 12:24 PM |
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Ive seen the Mumford link before, certainly wont work on my application, another axle control is using a 2" ball race mounted on the back of
the diff in line with the pinion, as per watts link, this bearing runs in a vertical track/channel mounted from the chassis on the centerline of the
car, The axle is FIXED along its centreline, can rise up and down and pivot about the pinion axis, total control as the expense of being high
maintenance and NOISIER than a noisy thing
Something different, Very different..............
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sprintB+
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| posted on 27/5/16 at 01:48 PM |
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I've never seen that written up before, interesting. Would like to see that ball race idea, I to have space problems temporarily fixed with a
ball piened hammer on the fuel tank flange.
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Sam_68
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| posted on 27/5/16 at 02:24 PM |
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quote:
Originally posted by sprintB+
Would like to see that ball race idea...
It used to be quite a common solution with 1950's de Dion axled race cars. Some quite famous cars like the Mercedes Benz W125, BRM V16,
Maserati 250F, Aston Martin DBR2 and Lister Jaguar used it. It's usually called 'sliding block' location. This is the Lister Jag
(diagram from Costin and Phipps):
As Ian said, the dual problems were maintenance (wear) and noise. Even the slightest bit of play in the slide block would make it bang and clonk like
hell. Possibly you could improve it these days, by using DU bushes sliding on a hardened steel rod (as in a damper) and isolated by mounting them in a
metalastic or polybush, but it's a lot of trouble to go to for a suspension system that's never going to be as good as a properly designed
IRS.
The other problem is that you can have geometry conflicts with other links: for instance if your sliding block wants to travel up and down in a
perfectly straight line, but your trailing arms want to make it move in an arc.
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sprintB+
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| posted on 27/5/16 at 02:47 PM |
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thanks for that, interesting.
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ian.stewart
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| posted on 27/5/16 at 03:27 PM |
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quote:
Originally posted by Sam_68
quote:
Originally posted by sprintB+
Would like to see that ball race idea...
It used to be quite a common solution with 1950's de Dion axled race cars. Some quite famous cars like the Mercedes Benz W125, BRM V16,
Maserati 250F, Aston Martin DBR2 and Lister Jaguar used it. It's usually called 'sliding block' location. This is the Lister Jag
(diagram from Costin and Phipps):
As Ian said, the dual problems were maintenance (wear) and noise. Even the slightest bit of play in the slide block would make it bang and clonk like
hell. Possibly you could improve it these days, by using DU bushes sliding on a hardened steel rod (as in a damper) and isolated by mounting them in a
metalastic or polybush, but it's a lot of trouble to go to for a suspension system that's never going to be as good as a properly designed
IRS.
The other problem is that you can have geometry conflicts with other links: for instance if your sliding block wants to travel up and down in a
perfectly straight line, but your trailing arms want to make it move in an arc.
The arc in the travel can be somewhat eliminated by using a double row tapered roller bearing or a balll race with thrust ratings, then you can run
the race up and down in a T slot
Something different, Very different..............
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Sam_68
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| posted on 27/5/16 at 03:38 PM |
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Yes, absolutely - there are ways around it (another is to use a form of longitudinal location that doesn't move through conflicting arcs, such
as the wishbone arrangement on the Veritas), but it's always added complication that is difficult to justify when it gets to the point that a
well-designed IRS is both technically superior and cheaper.
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