Everyone thinks that the traditional "single pivot axle with rope" steering will work. Everyone is wrong.
Rope and plank? just gonnae no...
A good example of pitman arm type steering, although the steering ratio looks quite low. The single tie rod between the steering arms means steering ratio can be adjusted without affecting wheel alignment.
Oh dear lord no. This is a crash waiting to happen.
Soapbox Steering Dos and Don'ts
Although it is fine for relatively low speeds, it becomes unstable as speed picks up because it is extremely sensitive and has no tendency to self centre. Watch the videos on the right for a example of the dreaded "speed wobble" and the inevitable result...
The most common form of steering currently in use is simple "gokart" or "pitman arm" steering. Steering racks salvaged from small cars are sometimes used.Here are some pointers on making your steering work.
- Don't go mad trying to make your cartie turn on a sixpence. It almost certainly won't need to be that manoeuvreable, and you probably only need to be able to turn your wheels through about 10 or 15 degrees.
- Don't have a direct link between your hands and the steering. Given that very small movements of the front axle are required to turn the cartie, you'll need to find some way to "gear down" your steering input so that relatively large hand movements only move the axle a small amount. This is called the steering ratio. A steering ratio of 2:1 is absolute minimum, and even that is going to be very twitchy. Anything approaching 1:1 is going to be very twitchy, and lesss than 1:1 is going to be uncontrollable and might not even be allowed in some cartie races.
- Stiffen up the steering. Make it relatively hard to move by fitting (e.g.) a motorcycle steering damper, which can be very effective at making steering more manageable and can be readily picked up quite cheaply from online auction web sites.
There are some great explanations of how to get the right steering geometry on the web sites shown below. Most of these sites are to do with the building of recumbent bikes and GreenPower racers, but the principles are exactly the same for gravity powered vehicles.
|A good explanation of Ackermann steering geometry, camber, caster, and centerpoint steering, and some really handy spreadsheets too. |
|Similar stuff to Peter Eland's pages, but with some good clear pictures showing all the angles.|
|A great way to make kingpins, using either bike steering tubes or from scratch using bushings and bolts.|
|Steering geometry for Gokarts - similar in many ways to the problems that need to be solved for a soapbox cartie.|
|More notes on caster, camber and toe. This is from the perspective of race car design, but it still contains some useful background information.|