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Suspension

The suspension of the car has a large influence on how well the car handles. Ideally the suspension of the car will keep the wheels pointed in the correct direction, allow the wheels to travel up and down as vertically as possible with as little wheel scuff as possible, absorb the forces generated by travelling over bumps or dips in the road and most importantly prevent the car from destroying itself as it drives over cattle grids.

No suspension system is perfect and the decisions you make must try to find a balance between these values. As this was our first ever suspension design experiment we probably could do better next time.

We chose double wishbone suspension because it is relatively light, well understood and easy to adjust the damping or the spring load.

Click on these diagrams to download the 3DMF models.

Mac users can view 3DMF in SimpleText or any QuickTime aware application, Windows users can download Apple's 3DMF viewer from

ftp://ftp.apple.com/developer/Quicktime/Windows_Tools/QD3D_Tools/QD3DViewer/QD3DViewer.zip

Eventually to test the design, a suspension mockup was created

The mockup pretty much proved what we suspected, that the wishbone arms were a bit too short. So we decided we'd expend the car out to 1900mm (extra 50mm on each side) and shrink the top of the frame by 20mm (the top wishbone mounts are 20mm closer in than the bottom ones). Actually, we haven't quite decided whether to make the frame sides not quite vertical or instead just bring top and bottom in 20mm and then retain the 25/45 top/bottom gap from the frame edge to the wishbone mount points.

Some simulations told us that the intended plan was going to work. We have built it and were relatively happy with it.

Our wishbone lengths are 215mm (bottom) and 180mm (top).

The steep angle of the caster does introduce some interesting side effects to the vehicle. The vehicle drives beautiful and straight. It also introduces a substantial lean to the car when you turn the vehicle. It would be nice to think this was leaning you into the corner but sadly it is not.

Our finished suspension on the car also required a stiffer shock absorber spring than we had initially guessed. This is largely due to the shock absorber being mounted on an angle and the group having no idea what was really an appropriate setting.