'Spin axis forward at given speed (0-255)
If no speed is specified then a value must have been previously set with axisClass.setSpeed()'

def forward(self, speed=None):

    if (speed == None):
        speed = self.speed
        if (speed == None):
            raise _RepRapError('Axis    speed    not    set')
    if ((speed >= 0) and (speed <= 255)):
        p = snap.Packet(self.address, snap.localAddress, 0, 1, [CMD_FORWARD, int(speed)])
        p.send()
    else:
        raise _RepRapError('Invalid    speed    value')
