Steady-State Turn Experiments, The Torque Wrench Bike
An interesting experiment at the University of Illinois focused on using an instrumented bike to ride in steady circular fashion. The objective was to clarify the matters of how much lean and in what direction is needed, as well as what magnitude of handlebar applied torque is required. The bicycle was instrumented, and was ridden on a special marked riding surface so as to be able to measure five important variables
The bicycle’s forward speed was measured with a standard bicycle computer.Steer torque was measured by the rider by use of a standard mechanic’s torque wrench affixed to the head of the handlebar stem.
Rider’s lean angle relative to the frame was measured using a pivoted rod connected to the back of the rider (in a position along the rider’s spinal cord); and this angle was measured by a voltmeter as the base of the rod was connected to a rotary potentiometer at the rod’s pivot point just beneath and behind the bicycle seat. The potentiometer was energized being connected to a conventional DC battery source (9 volt transistor battery). The voltage proportional to upper torso lean angle was displayed on a standard analog voltmeter affixed to the handlebars in view of the rider. The voltmeter was calibrated to indicate lean angle of the rider’s upper torso relative to the bicycle’s frame.
Lastly, the riding surface was marked with chalk in circles of known radii. This permitted the rider to maintain circular paths of known radii as desired.
Angle of turn was measured by the rider noting the angle of turn (of the handlebars) by observing a wire’s position affixed to the front fork relative to a common protractor attached to the frame adjacent to the steering head.
|The gist of the first experiment was to ride circularly at a given forward speed, and then hold the steer torque at a zero value (thus nulled about the zero value with fine adjustments) while using upper body lean articulation as the primary biasing steering control input. This experiment was repeated for a variety of bicycle velocities and radii. The object was to determine by measurement whether the rider leaned into or out of a turn and how much, as measured relative to the bicycle’s frame. The bicycle’s forward speeds and radii influenced how much and in what direction the rider had to lean.
|The second variation on the experiment was to essentially repeat the above experiments except that the rider’s upper torso was maintained in the plane of the frame of the bicycle. The rider applied a steer torque using the torque wrench affixed to the front fork steering head. As the bicycle was ridden in a steady state or continuous circle, the rider observed the indicators of the forward velocity, the angle of steer, and the rider applied torque on the handlebars. At UIUC we performed these experiments almost twenty years ago, and subject to minimal budgets. Hence, fancy computers and data logging devices were not employed, but instead we relied upon the rider observing key variables as measured by eye during riding, and orally shouting out values which were then recorded using a pencil and notebook by an assistant standing by.
|The results of the UIUC Torque Wrench Bike experiments were of considerable significance. In order to do justice to the discussion of the results, it now becomes necessary to introduce the concept of critical velocity of a bicycle.