Direct Drive Units

The Jefa direct drive is the strongest compact autopilot drive in the world. It's much stronger than a human being (the max. output torque of 375 KgM is equivalent to 375 Kg force on the end of a 1 meter steering tiller) and is build for 24 hours per day continuous operation with a total weight of only 19 Kgs. The combination of the specially designed electric motor with the ultra efficient 3 stage 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 45 to 55 foot equipped with a mechanical steering system that can be back driven.
The direct drive drives the rudder via a draglink and the existing tiller arm or quadrant or via an independent tiller arm. (see illustration)

Please click on the picture for a larger view.

Some mounting possibilities:

The left illustration shows the direct drive combined on the steering tiller lever. A long output lever is fitted to achieve the correct geometry. The right illustration shows a direct drive mounted on a separate lever independently from the steering system.

The three possible operation centres:

Direct drive operating centres in mm valid for 72° (2x36°) rudder travel.

The choice of multiple tiller centres is a great advantage over other drive units. Depending on the application, the appropriate centres can be chosen. When the direct drive operates on an independent lever, the small tiller centres are chosen. When the direct drive is combined with the steering on one lever, the 250 mm tiller centres are chosen. The 307 tiller centres are only chosen when there is no possibility to use the smaller tiller centres.

Main dimensions short version

The Jefa 375 KgM direct drive is very compact with a length of 304 mm, a width of 304 mm and a height of 252 mm. As space is always a problem on sailing yachts, the direct drive unit can be mounted as close as 250 mm from the rudderstock even upside down. The short version has an output lever centre of 130 mm to work with 200 mm tiller centres.

Main dimensions long version

The Jefa 375 KgM direct drive is very compact with a length of 304 mm, a width of 304 mm and a height of 252 mm. As space is always a problem on sailing yachts, the direct drive unit can be mounted as close as 250 mm from the rudderstock even upside down. The long version has an output lever centre of 165 and 200 mm to work with 250 and 307 mm tiller centres.

The construction

The above assembly drawing shows a cross section of the direct drive. The drive can be separated in 5 main parts: The electric motor (1 and 2), the three stage planetary gearbox (3) and the electro-magnetic clutch (4) and the 1:5 spur reduction gearbox (5). The Jefa direct 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 used in the Jefa drive units is not a standard industrial motor, but specially designed and produced for this application. This solution is more expensive but there are multiple advantages over standard industrial motors.

• The collector (1) is extremely big so a large contact surface of the coal brushes is achieved. The result of this is a very high efficiency under heavy load and a very small drop in speed at the maximum torque. (Only 25% loss of speed at full load compared to a stall situation (zero speed) with other brands of autopilot drives).
• The central motor shaft runs in ball bearings in stead of gliding bearings. This results in a higher efficiency, less noise and a much longer life time.
• A large flat wound rotor to achieve a high starting toque and an immediate response to the autopilot speed control signal.
• Specially produced magnets with an extremely long lifetime and field strength. (Normal magnets can loose up to 50% field strength over a couple of years).
• Exchangeable coal brushes to guarantee an infinite lifetime of the drive.
• Aluminium motor housing in stead of sheet steel plate to avoid corrosion.

Planetary gearbox: To achieve a correct rudder travel speed (hard over time) the electric motor has to be reduced in speed with a factor 486:1. Some autopilot drive producers use a worm reduction box, but the efficiency is extremely low as the gears rub each other. Some producers use a combination of a planetary gearbox with a 2 stage spur gear set (one small gear and one big gear), but this creates a much bigger unit with an offset to the centre and much heavier loaded gears. The best way to achieve this high reduction in combination with a high torque is a 3 stage planetary gearbox. It's also the most expensive way as every gear step has 4 gears in stead of 2 gears but the huge advantages overrule the higher price:

• 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 (4) and controlled automatically by the autopilot junction box. Jefa has developed a unique and patented engagement clutch. The solution is based on two electrically operated spring loaded clutch pins that engage and disengage the outer gear ring of last planetary gear step. This solution has multiple advantages over the existing friction plate clutches:

• Less friction to back drive the unit.
• Lower power consumption (1.3 Amp. at 12 Volt, 0.7 Amp at 24 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 equalise the forces so the the clutch can disengage, making the manual take over much safer. 

The performance

This performance table shows the relation between the consumed power and the output power. The red line shows the output torque against the needed amperage for the 12 volt unit and the green line for the 24 volt unit. The blue line shows the hard over time (time to travel 72° of rudder travel) of the drive relative to the output torque. Also visible is the strength of the drive unit related to man power. The unit is much stronger than a human being and can last much longer but one should note that when the unit is operated in the red zone, something is wrong with the trim of the boats and the sails should be adjusted to achieve lower rudder torques. The above table shows that the Jefa direct drive will steer the yacht even in the worst possible conditions. As the drive will mostly operate in the left green zone and will not continuously rotate, the average power consumption on 12 volts is 4 amps and on 24 volts 2 amps.

Connections:

This illustration shows the minimal components for a working autopilot configuration. Jefa autopilot drives work together with all mayor autopilot electronics. The connection of the Jefa autopilot drive to the autopilot junction box is quite simple. The two 1.5 mm² red and black wires have to be connected to the plus and minus of the autopilot clutch line. This will make sure that when the autopilot user engages the autopilot on the control screen, the clutch will engage and allow the autopilot motor to drive the rudder. The two 4 mm² red and black wires have to be connected to the autopilot drive output connection. Now the Jefa autopilot drive is integrated into the system.

Compatibility in 12 Volts.

Following table shows the maximum rudder torques at midships and full rudder that can be generated by the Jefa 375 Kgm direct drive in combination with various autopilot junction boxes. The hard over time (HO-time) states the time it takes the drive to travel the full 72 degrees of rudder travel when the speed control of the pilot is set to maximum speed.

Compatibility in 24 Volts.

Following table shows the maximum rudder torques at midships and full rudder that can be generated by the Jefa 375 Kgm direct drive in combination with various autopilot junction boxes. The hard over time (HO-time) states the time it takes the drive to travel the full 72 degrees of rudder travel when the speed control of the pilot is set to maximum speed.

Jefa direct drive units type 2

Part No.

Description

DU-DD2-12

Direct drive 375 KgM type 2 12 Volts

DU-DD2-24

Direct drive 375 KgM type 2 24 Volts

The Jefa 525 KgM is the big brother of the 375 Kgm version. The electric motor is the same, but the reduction gearbox is bigger. This results in a higher torque with a lower hard over time. This drive is suitable for boats from 50 to 70 foot length were the hard over time of 13 to 17 seconds is more appropriate. The drive can be used on boats equipped with a mechanical steering system that can be back driven.
The direct drive drives the rudder via a draglink and the existing tiller arm or quadrant or via an independent tiller arm.

Please click on the picture for a larger view.

Main dimensions:

The Jefa 525 KgM direct drive is very compact compared to it's strength with a length of 385 mm, a width of 385 mm and a height of 252 mm. As space is always a problem on sailing yachts, the direct drive unit can be mounted as close as 300 mm from the rudderstock even upside down. The tiller corresponding tiller centres are 250 and 307 mm.

The performance

This performance table shows the relation between the consumed power and the output power. The red line shows the output torque against the needed amperage for the 12 volt unit and the green line for the 24 volt unit. The blue line shows the hard over time (time to travel 72° of rudder travel) of the drive relative to the output torque. Also visible is the strength of the drive unit related to man power. The unit is much stronger than a human being and can last much longer but one should note that when the unit is operated in the red zone, something is wrong with the trim of the boats and the sails should be adjusted to achieve lower rudder torques. The above table shows that the Jefa direct drive will steer the yacht even in the worst possible conditions. As the drive will mostly operate in the left green zone and will not continuously rotate, the average power consumption on 12 volts is 4 amps and on 24 volts 2 amps.

Compatibility in 12 Volts.

Following table shows the maximum rudder torques at midships and full rudder that can be generated by the Jefa 525 Kgm direct drive in combination with various autopilot junction boxes. The hard over time (HO-time) states the time it takes the drive to travel the full 72 degrees of rudder travel when the speed control of the pilot is set to maximum speed.

Compatibility in 24 Volts.

Following table shows the maximum rudder torques at midships and full rudder that can be generated by the Jefa 525 Kgm direct drive in combination with various autopilot junction boxes. The hard over time (HO-time) states the time it takes the drive to travel the full 72 degrees of rudder travel when the speed control of the pilot is set to maximum speed.

Jefa direct drive units type 3

Part No.

Description

DU-DD3-12

Direct drive 525 KgM type 3 12 Volts

DU-DD3-24

Direct drive 525 KgM type 3  24 Volts