Jefa Steering Autopilot Linear Drive - LD100, 100 KgM

Summary: The Jefa Linear Drive is lightweight, compact and has very low power consumption. Its 100 KgM output torque is good for boats from 20 feet up to 45 feet and weighs just 6,6kg. The Linear Drive can be used directly on the existing tiller arm, via the quadrant or and independent tiller arm. 

Available in 12V only.

The Jefa linear drive is a strong and compact autopilot drive and much more efficient than existing hydraulic and electro-mechanical linear autopilot drive units. With a thrust of 400 Kgs on 250 mm centers it's much stronger than a human being (the max. output torque of 100 KgM is equivalent to 100 Kg force on the end of a 1 meter steering tiller) and is built for 24 hours per day continuous operation with a total weight of only 6,6 Kgs.

The combination of the flat wound (pancake) electric motor with the ultra efficient planetary gearbox results in an extremely efficient drive unit to keep the battery charging time to the minimum. The drive can be used on boats from 20 to 45 foot l.o.a. (or up to 100 Kgm rudder torque) equipped with a mechanical steering system that can be back driven.

The linear drive drives the rudder via the existing tiller arm or quadrant or via an independent tiller arm. Due to the telescopic draglink, the overall dimensions are as small as possible and the drive can also be mounted upside down when the installation space requires this.

Components

The drive can be separated in 4 main parts: The electric motor, the two step planetary gearbox, the electro-magnetic clutch and the final spur reduction gearbox. The Jefa linear drive has multiple advantages over existing integrated drive units. These advantages will be explained per section of the drive:

Electric Motor: The flat wound electric motor (pancake motor) used in the Jefa drive units is carefully selected for this application. Pancake motors have multiple advantages over normal electric DC motors:

• A large flat wound rotor to achieve a high starting toque and an immediate response to the autopilot speed control signal.
• A motor efficiency of 72,5% to achieve a minimal power consumption and maximal mechanical power output (compared to max. 50% efficiency of a normal DC motor).
• Compact main dimensions compared to achievable output.

Planetary gearbox: To achieve a correct rudder travel speed (hard over time) the electric motor has to be highly reduced in speed. Some autopilot drive producers use a worm reduction box, but the efficiency is extremely low as the gears rub each other. The Jefa linear uses a planetary gearbox which has following advantages:

• The highest possible efficiency compared to any other gearbox.
• All forces are equally spread over 3 gear teeth in stead of one allowing a much compacter and stronger solution.
• The forces and torques from the motor to the output shaft remain in the centre line of the drive unit, resulting in a higher efficiency and extremely reduces the loads on the housing and other internal parts.

Electro magnetic clutch: On the moment the mechanical steering system on the yacht is manually operated, the autopilot drive has to be disconnected from the steering system. This is achieved with the electro-magnetic clutch and controlled automatically by the autopilot junction box. Jefa has developed a unique engagement clutch. The solution is based on a electrically operated spring loaded clutch pin that engage and disengage the outer gear ring of the planetary gear step. This solution has multiple advantages over the existing friction plate clutches:

• Less friction to back drive the unit.
• Lower power consumption (0.7 Amp. at 12 Volt). When the clutch isn't powered, it's disengaged and engaged when powered.
• The clutch doesn't wear in time.
• More compact than any friction clutch.

• When the autopilot is switched off, the helmsman isn't suddenly confronted with the full rudder torque, but has to put loading on the wheel to equalize the forces so the the clutch can disengage, making the manual take over much safer.