Putting my Segbot into standby mode

Other Hardware Motors, Mechanics, Power and CNC
1

project: Segbot; using a MPU-6050 IMU, Atmega328P-AU, and a SAbertooth 2x25 controller
It's working great! However, when no one is on it, it will self balance okay in a perfect environment, but just a little bump will start it oscillating. The motor speed maxes out at 100% at about 30 degrees tilt, which is just about perfect for riding. With no load (person), and I set the motor speed to be 50% at 30 degrees, it sets by itself very nicely, and can not be made to oscillate.
So I need to detect when it is not being ridden, and change the motor mapping to standbyMapping, rather than RidingMapping.
What sounds like a workable solution is this: If the motorVal goes Negative (reverse) more than once a second, put it in StandbyMode. Longer than 1 second since the last Negative value, go back to ridingMode. It sounds easy, but I'm struggling with it. It's more than just reading a negative value, but reading a "change to negative from positive". Any help would be greatly appreciated.
See lines 11 & 12 of my motor code here. I need to do one or the other, depending on standby mode or riding mode:

void update_motor(){  // Update the motors
  static unsigned long prevTime;
  int motor1, motor2;
  if (millis() - prevTime < 30) return; //only do this every 30 ms
  prevTime = millis(); //update the time stamp
  maxPitch = 1500; //value from the MPU-6050, this makes 30 degrees the max tilt for 100% speed
  maxSpeed = 64;
  standbySpeed = 32;
  if (pitch < -3000) crash(); //we probably crashed
  if (pitch > 3000) crash(); //we probably crashed
  motor_speed = map(pitch, -maxPitch, maxPitch, -standbySpeed, standbySpeed); //standby mode
  motor_speed = map(pitch, -maxPitch, maxPitch, -maxSpeed, maxSpeed); // map the angle to the sabertooth controller range 1-64  
  if (motor_speed > 64) motor_speed = 64; //that's the maximum speed

  if (motor_speed > 0)  motor_speed = fscale( 1, 64, 1, 64, motor_speed, -1.4); //scale it to change slightly at low numbers
  if (motor_speed < 0)  motor_speed = fscale( -64,-1, -64,-1,motor_speed, 2); //scale it to change slightly at low numbers
  motor1 = motor_speed + get_Steering();  //add steering bias to motor 1
  motor2 = motor_speed - get_Steering();  //add steering bias to motor 2
  // assign final motor output values
  motor1 = 65 + motor1;                //64 is neutral for motor 1
  motor2 = 192 + motor2;               //192 is neutral for motor 2
  motor1 = constrain(motor1, 1, 127);  //constrain the value to it's min/max
  motor2 = constrain(motor2, 128, 255);//constrain the value to it's min/max
  if (!debugMode) Segway.write(motor1); //Send motor 1 speed over serial
  delay(1);  //sabertooth can only receive commands at 2000/second
  if (!debugMode) Segway.write(motor2);  //Send motor 2 speed over serial
   if (!debugMode) {
      Serial.print("Pitch: ");
      Serial.print(pitch); 
      Serial.print("\tMotorSpeed1: ");
      Serial.print(motor1);
      Serial.print("\tMotorSpeed2: ");
      Serial.println(motor2);
    }
}
2

You refer to motorVal in your problem description, but not in your code. So it is not clear what your proposed fix actually is.

You need to have a variable whose state indicates which of the two operating modes you are in. You need to have some logic which detects the criterion you propose, to switch from one mode to the other. And obviously, the two lines where you calculate motor_speed, need to be done separately for each mode.

3

For motorVal, I meant motor_speed.

Yes, I've figured out that the two lines mentioned will be the result of which state the machine is in.
If in standby mode:

  motor_speed = map(pitch, -maxPitch, maxPitch, -standbySpeed, standbySpeed); //standby mode

And if it's in riding mode:

  motor_speed = map(pitch, -maxPitch, maxPitch, -maxSpeed, maxSpeed); // map the angle to the sabertooth controller range 1-64

But the logic of keeping up with when the last time motor_speed went negative, if it does it more often than once per second. This is what I need help with.

4

You will need some code that looks something like this. You probably already realise this, but one can
never be too sure of that.

if ( mode == 1 )
{
     motor_speed = ......  ;    //  map() function for regular mode
}
else
{
    motor_speed = ....... ;    //  map()  function for standby mode
}
5

Well, you need to keep track of each transition between positive motor_speed and negative motor_speed.

The easiest way to do this, is to check when it goes from positive to negative, and remember that time, using the millis() function. If the time since the last such transition is in the range that you observe for this unwanted oscillating behaviour, then you switch to the standby mode. But if the time is shorter or longer than that, you don't. If the motor speed is trending downwards with values like.. 10, 8, 6, 7, 4, 2, -1, 1, -2, -4, -7

then, it has gone from +ve to -ve twice, in a very short space of time, but you may want to disregard that change because it is just "noise" in the trend.

Some code might look like this.