code: func (d *Driver) Throttle(speed float32) {
  	d.mutex.Lock()
  	defer d.mutex.Unlock()
  	d.cmd[2] = floatToCmdByte(speed, 0x7e, 0x7e)
  	d.cmd[10] = checksum(d.cmd)
  }
docs: // Throttle sends the drone up from a hover (or down if speed is negative)