How not to Die

Since the beginning of the Kornguth Derby there have been strict rules against both killing other racers (and/or spectators) and against dying. Despite the strict enforcement of these rules I and a few other racers have almost violated them.

So what happened? I decided that to go fast I needed a heavy car and I also wanted my weight over the wheel with the least rolling resistance. So I built a 3 wheeled car with a piece of railroad track as the main structural piece. I used a motorcycle wheel as the rear wheel with a seat mounted behind it so my weight would be further back. In front I had the front axle and steering mechanism from a old go cart which I had used in a previous race. Despite the length and weight of the railroad track I needed even more weight up front to keep the front end on the ground since my weight behind the rear wheels tended to make the front end lift off the ground. So I started digging through the scrap metal pile for heavy pieces I could weld on the front to act as a counter balance. I found a few pieces of 1” plate steel and a broken axle from a dump truck that was around 2” in diameter. I added a hand brake for safety’s sake and took it for a short test drive down the road. I was ready to go race. I had a car with tested steering, brakes and the weight to propel me to victory.

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Race Day, I load my 300lb car in my truck and drive it up to the top of the race course. My heat of the race starts and we are off down the hill. I get a bit of a slow start but quickly gain speed. I start to notice that my car has a tendency to wander back and forth as it picks up speed. I am catching the car that barely beat me last year so I don’t really want to slow down. As I get to the steepest portion of the course my car gets increasingly harder to control. I finally decide I need to slow down, but slowing down means taking a hand off the steering wheel to use the hand brake. I really want two hands on the wheel to steer but I desperately want to slow down. I grab the hand brake to slow down, as soon as I take my hand off the wheel, my car starts swerving back and forth as I try to steer with one hand and brake with the other. Thankfully I had installed a cross bar near the rear wheel so if the car tipped that bar would drag on the pavement and keep me from going all the way over. I am not sure which slowed me down more, my hand brake or the anti roll bar dragging on the pavement. I managed to get my car back under control and cross the finish line. I am not sure what would have happened to a spectator’s legs if I had crashed my 300lb car into them going ~40 mph but it wouldn’t have been pretty.

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What when wrong? First my brake required me to take a hand off of my steering wheel to slow down. Second I mounted my front axle tipped slightly so it would attach better to the railroad track.

Fixing the brake issue is easy. All I needed was a foot brake that I could use without taking a hand off of my steering. If I had handlebars and hand brake mounted to them would have also worked, as long as I could use it without letting to of the bars.

The steering is a harder issue to fix, first of all I discovered that having steering that is a little bit wrong is way worse than a lot wrong. If it is a lot wrong you crash at the top of the hill before you get up much speed and before there are many spectators. If it is a little bit wrong you get going way faster before you crash and there are more people and things to hit.

The thing that everyone gets wrong is the amount of trail or caster in their steering system. The basic rule is you need to have the axis of your steering a head of where your wheels contact the road. This will make your steering wheels want to align with the direction you are going, which is good. If you have the axis of your steering behind the contact point of the wheels they will want to flip around and go the other way, which is bad. Think of pushing a shopping cart, when you go forward the wheels in front follow nicely along but as soon as you backup the flip around and face the other way. The same thing happens with bicycle steering. If you hold a bike by it’s seat you can push it forward without touching the handlebars, if you try to back up the front wheel will turn and the bike will fall over.

If this sounds like a bunch of gibberish you can test your car by pushing it and seeing if it goes generally in a straight line without any steering input. You should not have to have your hands on the steering to go straight. Of course you can also go for a slow but cool looking car if you really are unsure about steering and you should have brakes to slow down in case things do start to go sideways.