VEX Robotics Wiki

Take Back Half is essentially an Integrator (the I portion of a PID Controller), but every time that the error crosses zero, the output is cut. This makes it a good option for use in velocity control, and it gained popularity in the 2015-16 Nothing But Net season of VRC.

A more in depth look at Take Back Half can be found in this forum thread: Flywheel Velocity Control

• Only one gain constant to tune - easier than PID
• Fast Response Time
• Decent stability except with exceedingly high gain

• Can only be used in velocity control applications

After initializing the tbh, initial output, and gain parameters:

error = goal - currentSpeed;                // calculate the error;
output += gain * error;                     // integrate the output;
if (signbit(error)!= signbit(prev_error)) { // if zero crossing,
  output = 0.5 * (output + tbh);            // then Take Back Half
  tbh = output;                             // update Take Back Half variable
  prev_error = error;                       // and save the previous error
}

RobotC Example