Linear Drive Unit Introduction; Inspection; Dismantling - Raymarine Autohelm ST6000 Service Manual

1. Linear Drive Unit
The linear drive unit comprises a belt drive reduction stage from the motor, a single
epicyclic gearbox and a two start recirculating-ballscrew to provide linear motion. An
electromagnetic clutch locks the outer ring of the epicyclic gearbox when drive is
required. The drive is unique in providing efficient drive combined with very smooth
backdrive at extremely low loads.

2. Inspection

Before stripping down or testing the drive unit, a close visual inspection should be
made to establish if the cause of the problem is external.
Poor mechanical installation where the unit can foul obstructions, particularly at the
end of stroke, can distort the drive module and lead to rough operation and high
backdrive loads. The drive module is assembled at Nautech in a dirt free environment
to precise limits. If disturbed, rough operation and high backdrive loads will result.

3. Dismantling

After removing the unit from the boat and to gain access to drive motor, drive belt,
clutch rotor or drive module the following steps apply:
a) Unscrew and remove the two caphead screws which secure the plastic dust cover
to the main unit (use 'M3' alien key). Slide the dust cover off the girdle tube.
b) Unscrew and remove the four M6 caphead screws with washers and the two long
hexagonal studs at the centre-sides of the master plate. Separate the mounting cover
assembly from the master plate assembly, after feeding the cables through the
grommet.
c) If servicing the clutch rotor assembly, remove it from the mounting plate by
unscrewing the central caphead screw which secures the assembly to the casting.
Note that the assembly is sprung loaded and care should be taken when removing.
d) If replacing the drive belt, loosen the three M6 caphead screws with washers
which secure the motor to the masterplate. With the tension taken off the belt it can
be slipped off both pulleys.
e) If replacing the drive motor unscrew and remove the three M6 caphead screws as
above and take the weight of the motor as it is released. Note that the power cables
are extended and passed through grommets in the masterplate. Remove the drive
belt.
f) If servicing the drive module, follow steps a) b) d) and e) above. Then remove the
circlip at the front of the clutch plate/ring gear assembly and withdraw the assembly.
Locate the leadscrew journal and carrier on a firm block to prevent bending the
journal and drive out the roll pin securing the carrier to the leadscrew (general
assembly).
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