Continuous Rotation Movement Panel

How to use the Continuous Rotation Movement Panel robot skill

Turns two continuous rotation servos (or two RC electronic speed controllers, which take the same PWM signal) into the robot's drive system.

This is a movement panel: once it is in the project, everything in ARCx that moves the robot - the Movement Joystick, the Wiimote, Movement.Forward() in a script, the Autonomous AI skill, a ROS /cmd_vel binding - drives these two wheels. Only one Movement Panel can be in a project at a time.

Requirements

• A connected EZB.
• Two continuous rotation servos, or two ESCs, one per side.
• Both wheels driven by servo ports (they can be on different boards).

Adding it to a project

1. Connect to the EZB.
2. Add the skill (Movement Panels category).
3. Open the configuration. For each wheel choose the servo port, then set its Max Speed Forward Value, Stop Value and Max Speed Reverse Value.
4. Save and press the arrow buttons in the skill's window.

Opening the configuration stops the robot first.

Setting the three values per wheel

A continuous rotation servo does not take a position, it takes a speed: one end of the servo range is full speed one way, the middle is stop, the other end is full speed the other way.

Because the two wheels face opposite directions on the robot, their forward values are at opposite ends of the range. That is why the defaults are:

To calibrate:

1. Set both wheels' values to the defaults and press Forward.
2. If a wheel turns the wrong way, swap that wheel's forward and reverse values.
3. If a wheel creeps when stopped, adjust that wheel's Stop Value a little either side of centre until it is still. Many continuous rotation servos need this trim.

The window

• Movement buttons - forward, reverse, left, right and stop.
• Left Speed and Right Speed - the current speed for each side, 0-255. These are ARCx's global movement speeds, so changing them here changes what every other skill commands as well.

How speed works

The speed, 0-255, is scaled between the wheel's Stop Value and its forward or reverse value. Speed 255 sends the full forward (or reverse) value; half speed sends halfway between stop and that value. Each wheel uses its own speed, so a script can set the two sides differently to drive in an arc.

Turning is done by driving one wheel forward and the other in reverse (a spin turn):

Configuration

The Window tab sets the robot skill's window title, its size on the workspace and notes about what it does in this project.

Troubleshooting

See also

• Movement Joystick - an on-screen pad that drives this panel
• Wiimote - a Wii Remote that drives this panel
• Auto Position (movement panel) - the alternative panel for legged robots

Control Commands for the Continuous Rotation Movement Panel robot skill

There are Control Commands available for this robot skill which allows the skill to be controlled programmatically from scripts or other robot skills. These commands enable you to automate actions, respond to sensor inputs, and integrate the robot skill with other systems or custom interfaces. If you're new to the concept of Control Commands, we have a comprehensive manual available here that explains how to use them, provides examples to get you started and make the most of this powerful feature.

This skill has no control commands of its own.

It is a movement panel. It is driven through ARCx's movement system, which means the Movement object in a script, not a ControlCommand() call.

Driving from a script

Examples

Drive a square:

Movement.SetSpeed(180);

for (var i = 0; i < 4; i++) {

  Movement.Forward(180, 2000);
  Movement.Right(180, 800);
}

Movement.Stop();

Drive in an ARC by giving each wheel its own speed:

Movement.SetSpeed(200, 120);
Movement.Forward();
sleep(3000);
Movement.Stop();

Moving the wheel servos directly

The wheels are ordinary servo ports, so Servo.SetPosition(port, value) will move them - but doing that behind the movement panel's back leaves ARCx thinking the robot is stopped. Use Movement unless you have a reason not to.