code: func (d *Driver) CounterClockwise(val int) error {
  	d.cmdMutex.Lock()
  	defer d.cmdMutex.Unlock()
  
  	d.lx = float32(val) / 100.0 * -1
  	return nil
  }
docs: // CounterClockwise tells drone to rotate in a counter-clockwise direction.
  // Pass in an int from 0-100.