DC Motor Control via PS2 Controller - need help adding a dead zone.

mattbutsko

Hey everybody, I need help adding a dead zone to spin code that was provided to me to control some DC motors wirelessly over Xbees. Sometimes the analog sticks on a PS2 controller don't go exactly back to zero, which causes slight movement from the motors even when you're not doing anything.

I've been working on this for a week now, and since I'm not a spin professional, I just can't crack it. Any help would be greatly appreciated. I believe something could be added to either "Xbee to Control Board 1.26.11" or "Servos_PEKIT", but I'm not one hundred percent sure. I've attached the files in a zip, there's five total. It should be pretty easy to understand for someone who knows what they're looking at.

Basically, I was thinking of somehow specifying a small range inside each axis' 0 to 255 such as 118 to 138, and the motors would only get the pulses if the axis is outside of that range, but if anyone has any better ideas, I'd love to hear them.

Thanks for looking.

JasonDorie

That's pretty much what the hardware vendors suggest you do (I've worked on PS2 games). I don't remember what the suggested dead zone is, but that's about right.

An "easy" way would be something like this:

  DeadZone := 20  'using your value, but this way it can be tweaked easily
  value := PS2.GetXAxis
  value -= 128  'make the value from -128 to +127
  if( abs(value) > DeadZone )   'is the value far enough from center?
    if( value < 0 )
      SetMotorSpeed( value + DeadZone )  'Value is neg, so add DeadZone to it to make the motor start at -1, decreasing
    elseif( value > 0 )
      SetMotorSpeed( value - DeadZone )  'Value is pos, subtract DeadZone to make the motor start at +1, increasing
    else
      SetMotorSpeed( 0 )

JonnyMac

Here's what I'm doing with small, somewhat-less-than-precise joysticks: on start-up I read the X and Y positions assuming this is the idle position when the joystick is released (of course, it will never go back to the exact spot, so a small dead zone is useful). With the neutral positions in hand I call the following method during the program to "fix" the reading (must be called for each axis).

pub calibrate(in, idle) 

'' Calibrate joystick input based on starting position
'' --   in: uncalibrated input
'' -- idle: startup (idle) reading

  if (in =< idle)                                               ' at/below idle point                              
    result := JOY_MID * in / idle                                  
  else                                                          ' above idle point          
    result := JOY_MID * (in-idle) / (JOY_MAX-idle) + JOY_MID

JOY_MID and JOY_MAX are program constants based on your joystick/adc.

Apply the dead zone after running this method and you should get better results.