I think most people use a Bronze bushing, or spherical bearing,for the middle pivot. Rod ends are typically used on the ends of the round links. You might be able to scale some dimensions from a decent pic.
the longer you can make it the better , space restrictions dictate the lenght most of the time along with the amount of travel needed. you don't want it to over center. the upper and lower bars should be parallel and have the same center to center measurement from each side of the frame.most of the center piviots i've seen were on a 3 to 4 '' radius mounted at a 30 to 45 deg. angle
A Mumford Link might be a lot easier. http://www.not2fast.com/chassis/mumford.shtml Should be able to mount it upside down,compared to the pics.
I have a lot of experience working with watts links. I have seen the bell crank mounted to the back of the rear end housing, the bottom of the rear end housing, around the pinion yoke, mounted to the frame behind the rear end, mounted to the frame under the rear end, mounted off to one side on the axle housing (1st gen RX7). I have worked with road race cars (trans-am, IMSA GTO/GTS1) that had the bell cranks as small as 4 inches link to link and circle track late models that were as much as 10 inches link to link. The first thing to remember is that the center of the bell crank establishes the roll center. The second thing to remember is that the links must be parallel at some point of the travel, preferably at ride height, and that when the links are parallel they are 90 degrees to the bell crank. Coming up with the actual dimensions is a matter of how much room do you have to work with and making sure that all of the components/mounting points will stand up to the forces that the components will bear, as well as making sure nothing will ever go into bind. If I recall correctly there is a very good explanation of watts links in the Carrol Smith book "Engineer to Win". For that matter you may want to get all of the Carrol Smith books, Tune to win, Drive to Win, Prepare to Win, and Nuts Bolts and Fasteners. Yes all of those books are directed at racing, yet almost all of it translates to hot rods. That and reading any of Carrol's books is like listening to him talk. The man was a genius with a very dry sense of humor.
Carol Smith was the KING! The "To Win" series is a definite must read for any prospective car builder.
Can't hurt, but is more of a factor in a standard panhard bar, where only two pivots are involved. I'd think as long as the watts link is setup up properly, you can get away with a relatively compact apparatus, but this is just my own brain telling me this, I'm NO engineer.... The Mumford is cool, I'm going to make a model of that to see it work. Plus it's always cool to say "Mumford".
I have worked on very fast, very hard cornering cars that were designed by people WAY smarter than me, that had watts links that the bell crank was no more that 4 inches link to link and the links were no more than 10 inches long. So yes, you can get away with a very compact watts link. Keep in mind the smaller the bell crank and the shorter the links. the less movement it will take before you run out of travel and everything goes into bind and eventually bang. On the other end of the scale, if you go large with the bell crank and long on the links the more likely you are to run into interference with the rest of the chassis, not to mention the added weight.
How much suspension travel on these race cars ? Longer links allow more travel,like on the street with air bags.
Not a lot, considering that the rear ride height on the cars with the compact watts links was set at 3 inches at the frame rail just in front of the rear tire. and they had even less body roll. That was the point I was trying to make, I guess I didn't do a very good job of it. The more travel you have the more span that the bell crank is going to have to have, and that you have to be careful in the design so that nothing goes into bind. My gut is the bell crank span should be at least as much as the suspension travel that you expect to have. One good way to figure it out is to build a scale model and run it through its expected travel. I have used that method with paper cut outs, tooth picks and graph paper.
This as a nice link to some explanations of different set-ups as well as working models to look at. Pretty good info. I also found out that nissan uses a Scott Russel link on some of it's new cars. http://www.brockeng.com/mechanism/index.htm
hey thanks for all the info guys its all helping out alot. any more pictures would be great. i have design in my head but its always nice to see what other come up with first.
I am using a watts link on an air bagged truck with truck arm suspension it has about 12" of travel,the links are 22.5 ,the bell crank is 12" but it is not at 90* to the links at ride ht it is about 15* from verticle. I have it mocked up and it seems to work fine. I am still wondering what to use for the center bearing how strong does this have to be? I will try and put up a pic in the morning
I would rather use an a-arm on top. The center point could attach onto the bridge for the bags. Brace the bridge to the frame,so it can't rack back and forth. Pic came from an old post by DollaBill,I think he used stock S-10 bushings for the ends.
Here is the wishbone that I built for an air ride equipped '55 Chevy truck. It locates the rear end side to side and controls axle wrap. It works awesome:
ian the pivot will have a poly bushing with a steel sleeve. the way i have it now its just to get the geometry set. i also have polys where it connects to the frame to cut down on noise and give at a bit of cush. the that rear set up that drive em posted is very nice. for my own car im a fan of complexity. not by choice.
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