Robotics, Automation & Control

A spherical induction motor (SIM) eliminates the robot's mechanical drive system.

SIMbot is an updated version of the ballbot, an elegantly simple robot whose tall, thin body moves on top of a sphere slightly smaller than a bowling ball. SIMbot features a motor with just one moving part: the ball. The other active moving part of the robot is the body itself.

The spherical induction motor (SIM) eliminates the robot's mechanical drive system.

The spherical induction motor (SIM) eliminates the mechanical drive systems used on previous ballbots. This means SIMbot requires less routine maintenance, and is less likely to suffer mechanical failures. The motor can move the ball in any direction using only electronic controls. These movements keep SIMbot's body balanced atop the ball. SIMbot is capable of a speed of 1.9 meters per second, or the equivalent of a very fast walk.

Induction motors use magnetic fields to induce electric current in the motor's rotor, rather than through an electrical connection. What is new here is that the rotor is spherical and can move in any combination of three axes, giving it omnidirectional capability. The SIM enables the ball to turn all the way around, not just move back and forth a few degrees.

Since SIMbot's body dynamically balances atop the motor's ball, a ballbot can be as tall as a person, but remain thin enough to move through doorways and in between furniture. This type of robot is inherently compliant, so people can simply push it out of the way when necessary. Ballbots also can perform tasks such as helping a person out of a chair, helping to carry parcels, and physically guiding a person.

The SIM rotor is a machined hollow iron ball with a copper shell. Current is induced in the ball with six laminated steel stators, each with three-phase wire windings. The stators are positioned just next to the ball, and are oriented slightly off vertical. The six stators generate traveling magnetic waves in the ball, causing the ball to move in the direction of the wave. The direction of the magnetic waves can be steered by altering the currents in the stators.

Eliminating the mechanical drive decreases the friction of previous ballbots, but virtually all friction could be eliminated by eventually installing an air bearing. The robot body would then be separated from the motor ball with a cushion of air, rather than passive rollers.

For more information, contact Byron Spice at This email address is being protected from spambots. You need JavaScript enabled to view it.; 412-268-9068.

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