I've. Build a watts link which is a strong piece i was wondering if anyone has information on properly setting one up . Does the dogbone center backet have to be at 90 degree at ride height or does that eve matter
The center piece doesn't move much at all from off the ground to fully compressing the suspension. When I built mine I did install the dog bone vertical.
I believe the bars should be parallel to each other. And that the pivot not bind at either full bump or droop, or be able to somehow reverse direction and jamb up the works entirely. Hopefully someone can confirm / correct that. Having the pivot point at axle height sounds like a good idea, too, but perhaps it wouldn't matter all that much? Gary
it does not matter where your center pivot point is in relation to the axle center... the most important thing is that, at ride height, both links are parallel to the ground and each other
The purpose of a Watts link is to center the frame over the rear axle through the suspension's full range of movement. To do so, the pivot must be centered between both wheels and both arms must be the same length. At static ride height it is best to have the pivot straight up and both arms parallel to the ground.
All you need to know and some animation too. http://en.wikipedia.org/wiki/Watt's_linkage Sent from my mobile Google link.
The pivot point height/location determines roll center. It's not a random, any place will do location. It does much more than locate the rear end. Google watts link and read up.
I disagree. It is the height of the center point above the ground that determines the rear roll center which in turn determines the rear roll axis. The roll axis is important in cornering as it affects body roll and tire loading. Not enough time here to go in depth - Google it or buy a chassis set-up book.
This link might be of interest, found it a while back, lots of good info on rear suspension, I hope it works, Murch. http://www.popularhotrodding.com/tech/0604_rear_suspension_guide/viewall.html Posted using the Full Custom H.A.M.B. App!
Wiki say.... Automobile suspension Watt's linkage as part of an automobile suspension Watt's linkage used in a 1998 Ford Ranger EV The above image with the linkage movement animated Watt's linkage is used in the rear axle of some car suspensions as an improvement over the Panhard rod, which was designed in the early twentieth century. Both methods intend to prevent relative sideways motion between the axle and body of the car. Watt’s linkage approximates a vertical straight line motion more closely, and does so while locating the centre of the axle rather than toward one side of the vehicle, as more commonly used when fitting a long Panhard rod.<sup id="cite_ref-7" class="reference">[7]</sup> It consists of two horizontal rods of equal length mounted at each side of the chassis. In between these two rods, a short vertical bar is connected. The center of this short vertical rod – the point which is constrained in a straight line motion - is mounted to the center of the axle. All pivoting points are free to rotate in a vertical plane. In a way, Watt’s linkage can be seen as two Panhard rods mounted opposite each other. In Watt’s arrangement, however, the opposing curved movements introduced by the pivoting Panhard rods are compensated by the short vertical rotating bar. The linkage can be inverted, in which case the centre P is attached to the body, and L1 and L3 mount to the axle. This reduces the unsprung mass and changes the kinematics slightly. This is used on Australian V8 Supercars. Watt's linkage can also be used to prevent axle movement in the longitudinal direction of the car; however, this is more common in racing suspension systems. This application usually involves two Watt's linkages on each side of the axle, mounted parallel to the driving direction. Herb Adams book 'Chassis Engineering' is the bible....
In your drawing it would be better to keep the horizontal bars as level as possible, or you are going to introduce sideways motion into the axle. Make a scale model out of cardboard or thin wood and cycle it through the travel and plot the movement.
I pinched that drawing but yeah, you mean like this diagram from above, if you turn your head to the side (to save me from building a scale model)? Dang, I have perfect mounting points on my housing already for the inverted link setup. So how short can the middle link be, for say a 4" suspension travel?
I played around with this a little. Using 20" bars and a 4" center link and compared a vertical (at ride height) center link to one angled 15 degrees (at ride height). With 6" of travel (3" up, 3" down), the vertical bar had .00195" of lateral movement at each extreme and the 15 degree center link had .007" of lateral movement at each extreme. It appears a vertical center link is better but the lateral movement of the axle either way is pretty minimal (at least with the dimensions I used).
As drawn, this is technically not correct. If the links are the same length and centered, the end link mounts should be the same vertical distance apart as the mounting holes on the rocker arm (dogbone). The links do not have to be horizontal or parallel at ride height, but they should become horizontal and parallel at some point in the suspension travel.
i would think a panhard bar would work fine on the street. i guess most of my cars had very little suspension travel to worry about.
DO NOT BUILD IT LIKE THIS ABOVE!!! [ It will move to the right on compression ] Watts Links are very simple and forgiving but there are a couple of basic rules to follow. The 2 links need to be equal so the arc they travel cancels each other out. And most importantly [ for a straight vertical path of travel ] When measuring the distance of the LH and RH mounting points from the ground, the difference in the heights must be exactly the same as the diameter [ I'll use the term diameter here to explain easier] of the bell-crank. If the bell-crank is 6" across [ 3" radius ] The left arm can be either mounted 6" higher [or lower] than the right side mounting point. When the watts goes through it's full range of movement , at one point both arms should be horizontal together The Watts doesn't need to be parallel or even in the centre of the car. I have seen them work quite successfully mounted horizontally under a diff-head [ with one link in front and one link behind ]
Yes, they can be offset for packaging if the ratio of link length to rocker arm length is maintained. Have a look under a first generation RX-7.
Yeah I totally forgot about that! On some oval cars Ive seen the Watts on the LH side of the rear-end in a car with a lot of LH weight bias [ trying to get the roll-axis inline with the CG Axis ] Ive also seen the Watts [and the front end geometry] used to shift the roll axis to the RH side to help create a more dynamic LH weight bias. Both cars worked OK once they sorted out all the corner springs.[ roll couple ] The problem with both of these cars was they tried to out-trick themselves by reinventing basic physics and engineering. They would got the same results by choosing the correct spring [ roll stiffness ] for the particular CGH over RCH application [ weight transfer thru overturning moment ] General consensus on oval cars is a Jake on the RH side is better for side bite [ on dirt with high amounts of body-roll ] When I first saw a horizontal Watts [ on an RX7 road racer ] they welded a giant bolt on the underside of the diff-housing to locate the centre bearing of the bell-crank. They had 2 nuts to adjust up and down the height of the roll centre.
The Jalopy Journal
