diff_steer.c

// Differential Steering Joystick Algorithm
// ========================================
//   by Calvin Hass
//   https://www.impulseadventure.com/elec/robot-differential-steering.html
//   https://github.com/ImpulseAdventure/
//
// Converts a single dual-axis joystick into a differential
// drive motor control, with support for both drive, turn
// and pivot operations.
//

// INPUTS
int     nJoyX;              // Joystick X input                     (-128..+127)
int     nJoyY;              // Joystick Y input                     (-128..+127)

// OUTPUTS
int     nMotMixL;           // Motor (left)  mixed output           (-128..+127)
int     nMotMixR;           // Motor (right) mixed output           (-128..+127)

// CONFIG
// - fPivYLimt  : The threshold at which the pivot action starts
//                This threshold is measured in units on the Y-axis
//                away from the X-axis (Y=0). A greater value will assign
//                more of the joystick's range to pivot actions.
//                Allowable range: (0..+127)
float fPivYLimit = 32.0;
			
// TEMP VARIABLES
float   nMotPremixL;    // Motor (left)  premixed output        (-128..+127)
float   nMotPremixR;    // Motor (right) premixed output        (-128..+127)
int     nPivSpeed;      // Pivot Speed                          (-128..+127)
float   fPivScale;      // Balance scale b/w drive and pivot    (   0..1   )


// Calculate Drive Turn output due to Joystick X input
if (nJoyY >= 0) {
  // Forward
  nMotPremixL = (nJoyX>=0)? 127.0 : (127.0 + nJoyX);
  nMotPremixR = (nJoyX>=0)? (127.0 - nJoyX) : 127.0;
} else {
  // Reverse
  nMotPremixL = (nJoyX>=0)? (127.0 - nJoyX) : 127.0;
  nMotPremixR = (nJoyX>=0)? 127.0 : (127.0 + nJoyX);
}

// Scale Drive output due to Joystick Y input (throttle)
nMotPremixL = nMotPremixL * nJoyY/128.0;
nMotPremixR = nMotPremixR * nJoyY/128.0;

// Now calculate pivot amount
// - Strength of pivot (nPivSpeed) based on Joystick X input
// - Blending of pivot vs drive (fPivScale) based on Joystick Y input
nPivSpeed = nJoyX;
fPivScale = (abs(nJoyY)>fPivYLimit)? 0.0 : (1.0 - abs(nJoyY)/fPivYLimit);

// Calculate final mix of Drive and Pivot
nMotMixL = (1.0-fPivScale)*nMotPremixL + fPivScale*( nPivSpeed);
nMotMixR = (1.0-fPivScale)*nMotPremixR + fPivScale*(-nPivSpeed);

// Convert to Motor PWM range
// ...