cmd_vel linear and angular relationship

cmd_vel

asked 2014-11-17 15:28:10 -0500

MarkyMark2012
1834 ●94 ●110 ●138

Hi All,

I'm using rqt robot steering to output cmd_vel message which I subscribe to and they control the power of the motors.

Linear is fine and +/-100% is controlling the motors fed and reverse okay. How should I combine that with the rotational input such that the effect is to increase or decrease the rate of turn? Just something simple is fine, this is a 2 wheeled robot.

The examples I keep finding on the internet seem to be simple key based designs. i.e. F=Fwd/L=Left etc...

Many Thanks

Mark

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answered 2014-11-17 19:32:43 -0500

kramer
1470 ●3 ●14 ●23

updated 2014-11-18 01:53:23 -0500

I think the following is what you're looking for. I'm not familiar with rqt's robot steering, so I'm assuming you're using geometry_msgs/Twist messages. If so, and assuming a differential drive robot, the usual method requires knowledge of the wheel separation (i.e., axle length) and wheel diameters.

void twistCb(geometry_msgs::TwistConstPtr &msg) {
  transVelocity = msg->linear.x;
  rotVelocity = msg->angular.z;
  double velDiff = (wheelSep * rotVelocity) / 2.0;
  double leftPower = (transVelocity + velDiff) / wheelRadius;
  double rightPower = (transVelocity - velDiff) / wheelRadius;
}