Jon White Posted February 13, 2007 Share Posted February 13, 2007 IIRC watts linkage is supposedly very good for anti tramp, and hence is often seen on the back end of drag cars. The problem is that due to the nature of it the rods can only be fairly short due to the width between the chassis rails. Therefore suspension travel is limited, as the watts linkage works best when the top and bottom rods are parrallel to the ground. Under extreme travel there is even the possibility of it turning itself inside out! Disco 2 set up seems to work for speed events but I'm not so sure you'll get extreme travel out of one! A front end type set up on the back (ie radius arms and a panhard rod) supposedly works well for speed events (eg safari racing) but again limits the travel and is not as good for low speed work eg trialling. 3 link is effectively whats on the back of a coiler as standard, and we all know the improvements in travel that can be made to the front end by 3 linking it. 4 links I've only really come accross on drag cars again. By making them adjustable lengths you can adjust the torque angles (or whatever its called) so gaining you ultimate traction under load. However I cant see much benefit on a 4x4, as launch traction isnt an issue. I would have thought you'd still need a panhard rod or something as otherwise you'd have no sideways control of the axle. I'm no expert though - these are just my thoughts! Jon Quote Link to comment Share on other sites More sharing options...
dollythelw Posted February 13, 2007 Author Share Posted February 13, 2007 I think the Woblink isnt gonna hit the spot, subterrainian roll centres and off road might prove tricky to package interesting setup though for halfwits like me theres pretty pictures of setups HERE Quote Link to comment Share on other sites More sharing options...
SOA 93 Posted February 13, 2007 Share Posted February 13, 2007 I think the Woblink isnt gonna hit the spot, subterrainian roll centres and off road might prove tricky to package interesting setup though for halfwits like me theres pretty pictures of setups HERE Before ruling it out completely bear in mind the design as I said was used for lowering the role centre, however the very reason I mocked it up was to see if it run upside down, and it does, you can also mount the links to the chassis not the axle as in the pictures, you could then have your roll centre 4" above your axle if you wanted and the links would come from one side of the chassis and be up out of the way. Or look at the picture and try to imagine the point identified as the chassis point is actually the where the axle is connected. I'll post pics later.... a thousand words and all that. Andy Quote Link to comment Share on other sites More sharing options...
dollythelw Posted February 13, 2007 Author Share Posted February 13, 2007 Before ruling it out completely bear in mind the design as I said was used for lowering the role centre, however the very reason I mocked it up was to see if it run upside down, I can dig that look forward to the pics - cheers Andy Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted February 13, 2007 Share Posted February 13, 2007 If I might wade into this intellectual discussion unarmed, if you raise the roll centre too high, are you in danger of creating a less stable car that doesn't show body roll before it falls over? ie plenty of weight transfer without the alarming roll angle that tells you it's time to go home. Quote Link to comment Share on other sites More sharing options...
dollythelw Posted February 13, 2007 Author Share Posted February 13, 2007 It would save those worrying moments though - Im ok, Im ok, Im ok, BANG...oh well....... Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted February 13, 2007 Share Posted February 13, 2007 "For sale: Ninety seat cushion in original unclenched condition. Heavy roll forces sale." Quote Link to comment Share on other sites More sharing options...
SOA 93 Posted February 13, 2007 Share Posted February 13, 2007 Ok here are some pics off my mock up of a woblink. First is the standard woblink. Same but articulating. Now we have the same but inverted, the axle and the chassis swap roles( ), the links are now mounted to the chassis and the axle just has a single pivot. Its just a complicated panhard rod really, with no arc of movement, wherever you choose to mount the axle pivot is where your roll centre will be. Land Rovers roll centre is the is the ball joint on the rear axle and where the panhard rod crosses the centre of the vehicle on the front axle, if you raise your vehicle by fitting longer springs or spacers you raise the front roll center by half your lift automatically. Lastly, inverted but articulating, the links don't need to be parallel, you could have them parallel at say, full bump then they stay up out of the way in normal running. Disadvantage of this system is the amount of pivots, but no worse than a watts linkage. Rakeway are using some bushes/joints on there racer they are off a RR sport or D3, Lem Forder or something, very well sealed and about £25 each I believe. Quote Link to comment Share on other sites More sharing options...
LR90 Posted February 13, 2007 Share Posted February 13, 2007 Those mock-ups are really good but I'm still not sure I follow it. Seems the roll centre is fixed (ish) on the last pic where the pivot mounts to the axle. But I say 'ish' as it would seem to move from side to side as the axle rises or falls (rather like a panhard rod setup I guess but looks much worse)? Quote Link to comment Share on other sites More sharing options...
dollythelw Posted February 14, 2007 Author Share Posted February 14, 2007 Ive got some cabinets that need knocking together Andy if you're interested? nice neat model looking at the pivot points Im wondering how strong I could make them without going truly mental? Many of the pivots would end up in single shear (which makes me nervy at the best of times) did your model give an indication how much vertical movement would be available or is that a product of the arc of the short "control" arm? Quote Link to comment Share on other sites More sharing options...
SOA 93 Posted February 14, 2007 Share Posted February 14, 2007 Ive got some cabinets that need knocking together Andy if you're interested? nice neat model looking at the pivot points Im wondering how strong I could make them without going truly mental? Many of the pivots would end up in single shear (which makes me nervy at the best of times) did your model give an indication how much vertical movement would be available or is that a product of the arc of the short "control" arm? If things get complicated or congested I find a modelling or templating it out of timber or MDF make it easier for me to understand or see if it fits Jez, I'm just a builder with an interest in suspension, I only suggested the woblink as an alternative to a watts, all the stuff I've read on watts suggest that the links should be parallel, which of course on the D2 they are not, I can't see why they need to be parallel, just equal in angle and length I would of thought. The inverted woblink does have some fabrication hurdles but I'm way out of my depth for those kind of questions. Regarding the watts linkage is there any reason it could not be mounted to the top of the axle so the pivot moved front to back rather than up and down, you'd get your roll centre above your axle again then. A couple more pictures of the inverted woblink with it at extended and compressed, the short link is 150mm long and gives about 200mm travel before it binds up on my model but I would think it would be better to say the travel is probably equal th the length of the short link. The floating link could be a lot shorter which would help with your strength issues, and of course the links could be made longer, as far as I know as long as you follow the formula in your posted picture you should be ok. By the way the picture you posted is scanned from ' Race and Rally car source book' by Alan Staniforth its where I got the idea from originally. Extended Compressed Quote Link to comment Share on other sites More sharing options...
dollythelw Posted February 14, 2007 Author Share Posted February 14, 2007 If things get complicated or congested I find a modelling or templating it out of timber or MDF make it easier for me to understand or see if it fits that works for me Andy - I tend to use card, Im sure wood hates me I would suspect that parallel control arms on Watts at rest would give equal movement of the bellcrank and of course if they were horizontal would give more vertical bang for your bellcrank rotational buck (in terms of distance the bellcrank would be required to move) as the arms cycle in their arc (thats such a carp explanation - hopefully if makes sense?) the control arms could be bought down pretty easily to get the horizontal and that would give the roll centre at the same height (or an inch or so lower) as a Rangie/defender "A" frame arrangement... hmmm theres still the voice in the back of my head saying 4 link is faster and more simple to build (for me simple is good - less stuff to break and service)... its a tough one this - but that just makes it more fun Quote Link to comment Share on other sites More sharing options...
missingsid Posted February 14, 2007 Share Posted February 14, 2007 OK it's thicko time again. Sorry. I understand Watts, and the Woblink (mostly) but I've only seen 4 link with either a Panard Rod or Watts. What type of 4 link are you looking at? Are you using outside links that are paralell to the chassis and 2 inside links that are at an angle to reduce sideways movement? as per old mark 3/4 cortinas I think? Cheers, Quote Link to comment Share on other sites More sharing options...
Bush65 Posted February 15, 2007 Share Posted February 15, 2007 OK it's thicko time again. Sorry.I understand Watts, and the Woblink (mostly) but I've only seen 4 link with either a Panard Rod or Watts. What type of 4 link are you looking at? Are you using outside links that are paralell to the chassis and 2 inside links that are at an angle to reduce sideways movement? as per old mark 3/4 cortinas I think? Cheers, The triangulated 4 link allows good control of the numbers for instantaineous centre, decreasing antisquat with axle droop, roll axis slope, roll center, roll/bump steer and articulation without binding. In practice, some compromises are necessary because something gets in the way of the links or mounts. The usual geometry for triangulated 4 link is: Looking from above, the lower links attach to the outer ends of the axle tubes and angle in to the chassis mounts. Parallel lower links give roll/bump steer, but triangulating them can reduce it to zero. Still looking from above, the upper links are widely spaced at the chassis mounts and they angle in to converge near the axle. This triangulation, if sufficient, will not have any problem handling the transverse forces on the axle/tyres. Looking form the side, the lower links angle up to the chassis and the angle between the upper and lower links converge somewhere forward of the chassis mounts. The location of the point where they converge is important for antisquat. In the side view, draw a line from where the upper links converge in the plan view and the point where the lower links converge in the plan view. This line is the roll axis. The upper links are made shorter than the lower links. This will reduce the antisquat as the axle droops. This is important when climbing on surfaces with good traction. A high roll centre is a big advantage on cross slopes. On a cross slope the centre of gravity leans over toward the low side. The body tilts about the roll centre, and if it is low, this shifts the centre of gravity even further. The result can be a roll over. If the roll centre is the same height as the centre of gravity the body will not roll at all. But roll centres this high are a disadvantage on fast uphill tracks, because the dynamics stiffen up the articulation. Quote Link to comment Share on other sites More sharing options...
missingsid Posted February 15, 2007 Share Posted February 15, 2007 Blimey Thanks for that I got about half of that first time of reading but should get better reading it again Dumb question time again. I may have seen this in a previous topic, does this mean that the RRC/LR rear setup with a A frame is 3 3/4 but not a full 4 link then? by sacrificing locational rgidity for lateral articulation? Quote Link to comment Share on other sites More sharing options...
Bush65 Posted February 16, 2007 Share Posted February 16, 2007 Blimey Thanks for that I got about half of that first time of reading but should get better reading it again Dumb question time again. I may have seen this in a previous topic, does this mean that the RRC/LR rear setup with a A frame is 3 3/4 but not a full 4 link then? by sacrificing locational rgidity for lateral articulation? By definition, a link can only provide axial restraint. An A-frame is not a link and it is not possible to have a 3/4 or 1-3/4 link. In practice, over a restricted range of motion, the rangie A-frame performs similar to triangulated upper links in a 4 link system. But because of the orientation of the bushes at the chassis end of the A-frame, and the ball joint at the axle end, the A-frame will bind at some stage during articulation or droop if considerably longer shocks than stock are used. The A-frame resists the transverse load, the same as triangulated upper links converging at the axle end. Because rangie lower links are parallel, when viewed from above, they suffer from roll/bump steer. But this is mainly an issue with raised suspension and a good amount of articulation. It may not be such an issue when you don't have good traction (eg mud). To understand how this works look what happens when the left wheel is pushed up toward the bump stop and the right is at maximum droop. Because the axle end of the lower links travel through an arc, the left wheel moves further back and the right moves further forward, thus steering the rear axle. Some times this will help, but at other times it will not (possibly steering into ruts that you want to avoid). No roll/bump steer is best. Quote Link to comment Share on other sites More sharing options...
callum Posted February 24, 2007 Share Posted February 24, 2007 perhaps misse dthe baot on this lot and i wouldn't profess to really understand but i saw this and thought of you as it were. http://www.rovertym.com/watts.htm seems some d2 owners may have issues. not sure how much help that is, if any. Quote Link to comment Share on other sites More sharing options...
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