Add LDO-42sth60-2004AC

[diberben]

Please add LDO-42sth60-2004AC which is used on Mellow VzBot330 kits Z-Axis:

[motor_constants ldo-42sth60-2004ac]
resistance: 1.4
inductance: 0.003
holding_torque: 0.6
max_current: 2.0
steps_per_revolution: 400

Thanks