The robotic monowheel: Gyrover.

The little robotic monowheel that could-Gyrover 2

Via: The Robotics Institute

"Consider a bicycle or motorcycle which has two wheels in the fore-aft (tandem) configuration. Such a vehicle is statically unstable in the roll direction, but achieves dynamic stability at moderate speed through appropriate steering geometry and gyroscopic action of the steered front wheel. Steering stability generally increases with speed, due gyroscopic effects. Dynamic forces at the wheel-ground contact point act on or near the vehicle centerline, and thus produce minimal roll disturbances. Additionally, the bicycle can remain upright when traveling on side slopes. Thus, sacrificing static roll stability enhances the dynamic roll stability and permits the vehicle to automatically adjust to side slopes.

As a logical extension of this argument, consider a single wheel rolling down an incline. Under the influence of gravity, gyroscopic action causes the wheel to precess (the axis of wheel rotation turns) about the vertical axis--rather than simply falling sideways as it does when not rolling--and the wheel steers in the direction it is leaning. The resulting curved path of motion of the wheel on the ground produces radial ("centrifugal") forces at the wheel-ground contact point, tending to right the wheel. Dynamic disturbances due to surface irregularities act through or near the wheel's center of mass, producing minimal torques in roll, pitch and yaw. The angular momentum of the wheel, in addition to providing the natural gyroscopic steering mechanism, tends to stabilize the wheel with respect to roll and yaw. In terms of attitude control, the wheel is practically insensitive to fore/aft and side slopes. The result is a highly stable rolling motion with minimal attitude disturbances and tolerance to fore/aft and vertical disturbances. One can readily observe this behavior by rolling an automobile tire down a bumpy hillside.

"Gyrover" is a novel, single-wheel, gyroscopically stabilized robot concept. The behavior of Gyrover is based on the principle of gyroscopic precession, as exhibited in the stability of a rolling wheel. Gyrover supplements this basic concept with the addition of an internal gyroscope nominally aligned with the wheel and spinning in the direction of forward motion. The gyro's angular momentum produces lateral stability when the wheel is stopped or moving slowly. A tilt mechanism enables tilting the gyro's axis about the fore/aft (roll) axis with respect to the wheel. Because the gyro acts as an inertial reference in attitude, the principal effect of the tilt action is to cause the wheel to lean left or right, which in turn causes the wheel to steer (precess) in the direction of leaning. Torques generated by a drive motor--reacting against the internal mechanism which hangs as a pendulum from the wheel's axle--produce thrust for acceleration and braking.

During a year of preliminary work, Gyrover has grown from an improbable yet intriguing concept for mobility, to the reality of working vehicles. We have studied the feasibility through basic analysis and simple experiments, and designed and built two, radio- controlled (RC) working models. These have proven the concept workable, and have verified many of the expected advantages"