Wednesday 11 May 2011

Let's analyze the suspension a bit.


OK, lets get down to details a little bit. Sorry for the huge images, but it's the only convenient way to show-and-tell. I'll refer to the top picture as p1 (the old design) and the bottom as p2, obviously. (which is the new design)

Right. Now, the first problem I had was the shock transmitter, as I call it. It is the triangle between the shock absorber and the rod that connected to the bottom wishbone. It's purpose is to transmit the shock energy to the damper by rotating about the axis (the red line without arrow). As you can see the transmitter is mounted on a single axis that is extruded from the chassis. This creates a problem: when the lower wishbone is raised, it creates a force on the point of the rotation, that goes upwards. Because the pivot point is welded to the chassis, it creates a moment; it wants to rotate in the direction of the shorter arrow. This creates the first problem - lack of rigidity and increased chance of mechanical failure.

The second problem is marked with blue arrows. It's the design of the transmitter itself. I did some testing with Autodesk Inventor, and the results were shocking (well, not really, but to increase the drama, let's say it was shocking): the structure would bend in an arc. (as noted by the blue line)

Now these problems were fixed in the new design, the p2 image. As the double-transmitter design is now being used, it eliminates the need of the rotation about the axis. It still has some force going in line to the rod (wishbone to transmitter) that wants to bend the pipe of the chassis, but it is being supported by the horizontal beams going across the chassis.

Image No 2:
Here you can see the common error of the transmitters.  Transmitting the shock 1:1 ratio to the damper (it should work as if the shock absorber was mounted instead of the rod). The mounting points should have the same radius relative to the center of the red circle. Which the old design didn't have.

If you are going to use this type of suspension design,  remember that the transmitter rotates about an axis. It won't move forwards and backwards in line with the shock absorber. It will rotate. The bigger the diameter of the transmitter is, the smaller arc of rotation you will get. That is good, that means that the shock wont move around a lot. Though it will move a little bit, that is why I have introduced an angle between the shock absorber and the chassis pipe, so It will have some space for that little bit of rotation.

The small circle in the a1 represents a very high friction force because it has to withstand the rapid smacking from the bottom. The a2 has an ability to cope with this much better.

Well, that's pretty much it. Sorry for the plain information. It might have been a bit boring for a normal person to read this..

Hope this was any help to You.

No comments:

Post a Comment