Nisso-Denko (Window) Motor Locking Pins

From DEW Robotics
Jump to: navigation, search

Team 1640's 2010 BREAKAWAY robot, DEWBOT VI is equipped with a novel, award-winning multi-mode, 4-wheel independent pivot drive-train. Kit-of-Parts Nippon-Denso Window Motors were selected as steering motors for the four (4) pivots. These steering motors are driven by tan Jaguar motor controllers.

1640 has experienced on-going, intermittent lock-up of the steering motors during practice and competition. Symptoms are:

  • One pivot suddenly ceases to respond to control, becoming locked at current angle
  • Wheel drive (CIM) continues to operate. So do the other pivots' steering
  • Motor at low temperature when lock-up occurs, but rapidly becomes too hot to touch.
  • Jaguar LED indicates that full power is being provided to the locked motor.
  • Voltmeter confirms that full power (12 V) is being provided to the locked motor.
  • Either unplugging the Jaguar PWM cable, or "rebooting" the robot corrects the lock-up.
  • Lock-up has been experienced with all wheels, although it appears to occur more frequently with some (wheels 1 & 4) than others (2 & 3).
  • Locked-up motors are not mechanically constrained from turning.
  • Anecdotally, lock-ups may be associated with aggressive steering maneuvers.

The problem was noted at both PARC and Monty Madness. It has been experiences as well during driver practice and at demonstrations.

Mentor Gary Deaver, following a thread on Chief Delphi cited incompatibility between Jaguars and Window Motors. The problem encountered by other teams appears to be the same as the one we encountered (intermittent lock-up). Many responses indicated that switching to Victors solved the problem. One indicated that the new Black Jaguars avoided this problem. Others cited the motor's internal positive temperature coefficient (PTC) resistor as the problem's source.

Replacing tan Jaguars with Black Jaguars did not solve the lock-up problem.

Drilling templates were prepared for switching to Victors, but before we executed on the Victor change, Gary Deaver cited the existence of locking pins within the Window Motor drive. These locking pins lock the drive coupling in one direction in response to excessive torque.

A spare motor was first disassembled. Pins located and removed. Then reassembled and tested.

This process was then repeated for the robot's four (4) installed steering motors.

Initial testing of the drive is promising. No lock-ups (yet). More testing is needed to know whether we've solved the problem.