'Steery Theory'

'Steery Theory' by Graham Swallow

So, you have completed your new pride and joy. Next comes the fun part, running it. Hang on a minute though, hadn't we better understand a little bit about how our new creation works before we let it off into the unknown.

Without a doubt the first question we get asked by the general public when they see our racing motorcycles is 'how does it stay up mister?' So here is my attempt to share with you my understanding of how these things work.

Straight Lines

For a two wheeled vehicle to move in a straight line requires very little technology. My first two wheeled 'toy' at age 9 or thereabouts was the famous Evil Knieval stunt cycle. (If you don't remember it ask a grown up). Basically you would wind up the little flywheel inside the bike and it would shoot off at great speed across the living room in a dead straight line. The beauty of it's straight line accuracy was that you could attempt such heroics as 'the coffee table canyon leap', though just like the the real Evil, it would usually end in tears... anyway, I digress. The point I am trying to make is that any well balanced bike with one wheel following the other will quite happily move in a straight line given a means of thrust. i.e. pedals, motor, hill etc. The clever bit is making it steer.

Steering Part 1

Ok, so this is where things get a little bit technical. To simplify matters we can break the steering process down into 3 elements:

	Lean into Corner
	Turn
	Lean out of Corner

Lean into corner
As I said, under power a 2 wheeled vehicle is naturally stable in a straight line. To make it turn, we must upset the balance. This is done by turning the handlebars. Now to lean any 2 wheeled vehicle to the left we must turn the bars to the right and vice versa. Sounds daft, but this is the same for all traditional two wheeled cycles (go try it if you don't believe me). This back to front effect is called counter-steering and is much talked about in full size motorcycling circles (excuse the pun). In our case counter-steering doesn't turn the bike, it merely shifts the weight over to one side or the other.

If counter-steering would turn the bike successfully alone, we would not need the soft sprung steering linkage attached to the servo arm, and this page would be much shorter. We can demonstrate counter-steering on a bicycle. If you counter-steer and keep the handlebars at the same angle you lean and lean and fall off the side of the tires and crash (don't say I didn't warn you!).

So why hasn't this happened to you up to now? What actually happens is that automatically, your brain tells you to stop counter-steering once the bike is leaned over, this allows the front wheel to follow the path of the corner by itself. This leads us nicely into section 2 of this steering tutorial ..... the turn.

Steering Part 2

The Turn
Once leaned over, the counter-steering stops, or else the bike will fall over as we have already described. The effect of the non-rigid sprung steering system on the model is to take the place of a rider on a real bike. The springing allows the bike to automatically override the servo steering inputs. The best way to demonstrate how the steering works mid corner is to use the example of riding a bicycle no handed. The front wheel finds it's own way round (the castor effect, as we'll call it) because of the shift in rider weight. You can see this effect on your model bike if you hold it upright on it's wheels and lean it over. The front tire will move in the direction of lean all on it's own, even if the steering servo is centered. The animation below shows the castor effect in action.

Steering Part 3

Lean out of Corner
The third element is identical to the first, but in the opposite direction. Remember the bike naturally wants to move in a straight line so less or even no counter-steering is needed to exit a corner than to enter it. The throttle control can be used to straighten up the bike. Remember the slower the bike is traveling, the more responsive it will be to steering inputs. Practice will show that you adjust the direction as much if not more with the throttle and brake than the steering control. Model car racers' usual reaction when 'driving' a bike for the first time is that it has no steering. Bikes are always less eager to change direction than cars, but this is half the appeal, it requires the user/driver/rider(?) to develop a little more finesse in order to be successful. Just for the record, my model bike is only 4 seconds per lap slower than the 1/5th scale 22cc radio controlled cars around my local track.

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