diff-steer

Provides a simple interface to a differential steering algorithm to control two motors from one two-axis joystick.

Installation

npm i diff-steer --save

Usage

diff-steer accepts two inputs, a x-axis value and a y-axis value from a two-axis joystick. The first argument is the x-axis (from -1 to 1) and the second argument is the y-axis (-1 to 1):

var diffSteer = require('diff-steer');
diffSteer(0, -1); // UP
// > [255, 255]
diffSteer(0, 1); // DOWN
// > [-255, -255]
diffSteer(-1, 0); // LEFT
// > [-255, 255]
diffSteer(1, 0); // RIGHT
// > [255, -255]
diffSteer(0.8, -0.74); // UPPER RIGHT
// > [255, -5.100000000000005]

The return value is an array of motor speeds for each motor ranging from 255 to -255. A positive number is "forward", and a negative number is "backward". You can then use those values however you need to.

It is configured out of the box to work with USB gamepads. For more information on interfacing with USB gamepads, checkout gamepad or node-gamepad.

Additional Configuration

Axis Input values

If your device does not return values between -1 and 1 for each axis, you can configure diff-steer:

diffSteer.maxAxis = 1023;
diffSteer.minAxis = 0;

UP/DOWN values

USB gamepads return a negative number of UP and a positive number for DOWN. If your device does not follow this pattern (or you'd prefer a different control scheme), you can flip the axis:

diffSteer.maxAxis = 1023;
diffSteer.minAxis = 0;

Johnny-Five

If you are using Johnny-Five, you can pass your five.Motors collection to the motor_control module and diff-steer will handle driving your motors for you:

var steerMotors = require('diff-steer/motor_control');
// Refer to J5 docs for more info on motor shield configs
var config = five.Motor.SHIELD_CONFIGS.ADAFRUIT_V1;
var wheels = new five.Motors([config.M1, config.M2]);
// ...
gamepad.on('move', function(id, axis, value) {
  if(axis == 0 || axis == 1) {
    var device = gamepad.deviceAtIndex(id);
    steerMotors(wheels, device.axisStates[0], device.axisStates[1]);
  }
});

If you'd rather control the motors yourself, motor_control also returns an array of motor commands:

var motorCmds = steerMotors(null, device.axisStates[0], device.axisStates[1]);
console.info(motorCmds);
// [
//   {
//     direction: 'fwd',
//     speed: 255
//   },
//   {
//     direction: 'rev',
//     speed: -255
//   }
// ];