steering

two approaches: cart-type steering where the entire front axle pivots to steer wheels (as in traditional soapbox racers), and kingpin based car type steering.

Cart type has the advantage of simplicity. The axle is controlled by cables attached outboard and either to a pulley and wheel control for driver or just 2 cables with handles (see soapbox derby construction manual). Two main disadvantages: the wheels will scrub more the tighter the corner turned. Maybe its not a big negative on the Canary Derby course, I think the tire scrub is really only a factor in turns less than 180′ radius (that radius comes straight out of my butt, can’t reference it). But the other negative is the effect that applying front brakes (if used) would have on steering. Most likely the brakes would not apply perfectly evenly to both wheels at the same time, resulting in a steering effect. This would be a problem if you had to brake suddenly. Similarly bumps on the road can have the same effect. A lesser disadvantage is that cart type steering does not provide any steering “feel” or self-centering.

Kingpin type steering has geometry that if set up correctly, provides steering “feel”, self centering, no bump or brake steer, and little if no tire scrub on corners. Its the type of steering used in cars. The kingpins are connected by a cunning arrangement of pivots and connecting rods, either to a steering box (rack and pinion often) or to steering “levers”. This type of steering is more complicated to construct and its debatable if it really has a big advantage over axle steering on the Canary course. Some cars last year did have it, looking totally cool and got a lot of compliments, two bonuses in my book. Have a look at the steering links on the side, and also Google for “Ackermann steering” for more info.

And a couple more points…

If you decide on the cart type steering, remember to install some sort of limit to the amount of travel the axle can make. Otherwise there is a possibility of major over steer (again, see soapbox derby construction manual).

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