Nice piece on the difficultly of reprogramming your brain to steer in the opposite direction as normal
Jason Moore
kyle
Fascinating video - interesting how much quicker his son was. I've
driven on the left hand side of the road for over 100,000 miles in
Australia, New Zealand and England. It is easy to switch back and
forth. I wonder if he will be able to ride both kinds of bike as
easily?
Chet
Jason Moore
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andy ruina
Anthony Doyle
The question asked was what was the controlling variable when a human rides a bicycle? In the early eighties I researched into this question for my Phd. I am not saying that what I found is universal because I only used two subjects but for those two the following applied. First both were blindfold throughout the trial. I subsequently found that a dozen competent riders chosen at random had no difficulty riding on an open space without hazards with their eyes closed though some of them needed quite a bit of persuading to try because they believed it to be impossible. From this I concluded that although vision can play a part in bike control it is not necessary. Both trial members had little difficulty riding an approximately straight course and none at all in keeping control at a slow speed. At no time did either subject put a foot down or lose control during a trial run. The bike was modified to remove all stability, that is the steering shaft was vertical and there was a counter rotating front wheel to remove its gyroscopic effect. A highly sensitive accelerometer was mounted in the roll plane and this and the movement of the steering shaft were recorded. The subjects brief was simply to ride slowly without falling off. They were not required to ride in a straight line but they did. An analysis of the records showed that the correcting movement of the handle-bar was initiated when the roll acceleration reached a fairly constant threshold. Because of the physical properties of man and bike the roll acceleration keeps on increasing with angle of lean. The human vestibular system is very sensitive to accelerations but more or less blind to velocity as may be observed when travelling in a lift. This means that the human control system cannot be modified by adding in some velocity. Any attempt to keep moving the handle-bar till the acceleration stops leads to dramatic over-control as can be observed when watching someone trying to ride a bike for the very first time. The strategy that is adopted, one that can be found in the control of other extremely unstable systems such as helicopters, is to make a more or less standard ‘spike’ of acceleration, a quick twist of the bar in the relevant direction followed swiftly with a return to its previous position. This action injects a pulse of energy into the control system which either reduces or reverses the roll velocity. In most cases it reverses the roll velocity and the bike goes over the vertical and starts to fall in the opposite direction so that it proceeds in a series of oscillations in the vertical, something that could also be seen very clearly by examining the tyre tracks. The earlier the correction is applied the less it needs to be but it looks as though the pulse itself remains more or less standard. When more energy is required a second or third pulse is applied in quick succession. All this takes place at time intervals that are well below the human conscious threshold which is why you can’t learn to ride a bike by thinking about it.
Riding a bicycle very slowly is difficult because the automatic stability effect more or less disappears and the rider has to provide all the control. When there is strong front wheel stability, control is quite different. For example, for normal road control on a motor-bike, where the offset steering axis and high gyroscopic forces produce a very powerful correcting response to both acceleration and velocity in the rolling plane, the rider simply alters the ‘zero setting’ of the system by pushing the handle-bar on the side to which he desires to turn. The immediate response is a roll in the direction of push which then provokes a correcting response from the automatic stability. The rider keeps the push while allowing the bar to adjust is position under the influence of the three torque forces, fork geometry, gyroscopic precession and his push. In doing this he is applying a torque that is independent of the bar’s position. The stronger the push the steeper the resulting turn.
For all the details google A J R Doyle Bicycle Riding; the theses is on the net.
andy ruina
andy ruina
On May 10, 2015, at 4:57 AM, Anthony Doyle <yodel...@gmail.com> wrote:
