The Rolling Stone
A Spherical Wheel Drive Mechanism
 

Project Overview

The Team

How it Works

Software, Control and Electronics

The Build
 -Structure
-Friction Drive
-Tension Wheel
-Electronics
-Assembly

Applications and Advantages

Materials

Obstacles and Challenges

Video

 

 

 

 

 

How it Works

Friction pressure between the polyurethane ball (2) and the rubber o-rings on the drive rollers (3) is provided by a third “tension” wheel (4) which simply consists of a ball bearing attached to a spring that pushes the spherical wheel into the drive rollers.  This is very similar to the tension wheel that can be found in a mouse ball. 

The three spherical caster “training wheels” (5) provide stability for the cart and can turn in any direction while the top spherical caster (6) makes sure the spherical wheel stays vertically aligned with the drive rollers.

The DSP circuit board (7) controls the relative speeds of the drive motors.  It takes user inputs from the RC controller and correspondingly drives the motors at the necessary speed to produce the desired direction of motion.  Encoders (8) relay information back about how fast the drive rollers are turning so that corrections can be made by the DSP in real-time. 

  • Conceptually similar to an inverted mouse ball

  • Rollers (1) placed at a right angle to each other drive the sphere (2), one for forwards, the other for sideways motion

  • Variation of the relative speed of the rollers through control of their 12V motors allows ball motion in any direction

  • Friction pressure between rubber o-rings (3) on rollers and the polyurethane ball is provided by a third “tension” wheel (4), similar to that in a mouse ball.  The third tension wheel consists of a metal ball bearing on the end of a spring-loaded plunger

  • Three spherical caster training wheels (5) provide stability for the system and can also move in any direction

  • The top spherical caster (6) makes sure the ball stays aligned vertically with the rollers and acts as the system’s load bearing

  • DSP circuit board (7) controls the relative speeds of the drive motors based on user inputs through an RC controller.  The software correspondingly drives the motors at the necessary speed to produce the desired direction of motion.

  • Encoders (8) relay information back to the DSP about how fast the drive rollers are turnings so that corrections can be made in real-time