4-Wheel Pivot Drive

4-Wheel Independent Pivot-Wheel Drive describes a 4wd drive-train in which each of the (4) wheels are independently driven and may be independently pivoted for steering purposes. The design offers the potential for excellent drive-train performance and a solution to conventional (tank) drive-train design constraints. The design also brings some clear design and control challenges.

This arrangement provides the possibility to operate in several Drive/Control different modes:

1. Crab mode – pivots all wheels together and at common speed to steer the robot in any direction on the 2-d playing surface (true 2-d drive). The mode does not control chassis orientation.
2. Snake mode – pivots front and rear wheels in opposite directions to guide the robot through a turn
   1. X-bias – drive direction aligned with the long-axis of the robot
   2. Y-bias – drive direction aligned with the short-axis of the robot
3. Automobile mode – pivots front wheels only to guide robot through a turn
   1. X-bias
   2. Y-bias
4. Tank mode – Does not use pivots to steer (but can use pivots to change drive orientation ala Twitch). Steering accomplished by differential L & R drive speeds.
   1. X-bias
   2. Y-bias

Overview

Inventor view of VEX Pivot Prototype

A detailed Mathematical Analysis of the Pivot-Wheel System is available in pdf format.

During the Team 1640 2009 Summer Program, a Vex-scale 4-Wheel Pivot prototype was designed, built, programmed and tested. While Vex-scale, the prototype was equipped with an FRC cRIO controller. This provided realistic (FRC-like) control of the prototype, allowed an accurate assessment of control capabilities and problems, and also left us with transportable code and useful programming experience.

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