def on_velocity_change(obj=nil, &block)
      @on_velocity_change_obj = obj
      @on_velocity_change = Proc.new { |device, obj_ptr, index, velocity|
        yield self, @steppers[index], velocity, object_for(obj_ptr)
      }
      Klass.set_OnVelocityChange_Handler(@handle, @on_velocity_change, pointer_for(obj))
    end
def on_velocity_change(obj=nil, &block)
      @on_velocity_change_obj = obj
      @on_velocity_change = Proc.new { |device, obj_ptr, index, velocity|
        yield self, @steppers[index], velocity, object_for(obj_ptr)
      }
      Klass.set_OnVelocityChange_Handler(@handle, @on_velocity_change, pointer_for(obj))
    end
Sets a velocity change handler callback function. This is called when a stepper velocity changes.

 @param [String] obj Object to pass to the callback function. This is optional.
 @param [Proc] Block When the callback is executed, the device and object are yielded to this block.
 @example
     st.on_velocity_change do |device, stepper, velocity, obj|
       puts "Stepper #{stepper.index}'s velocity has changed to #{velocity}"
     end
 As this runs in it's own thread, be sure that all errors are properly handled or the thread will halt and not fire any more.
 @return [Boolean] returns true or raises an error