direct drive unit type DD2


Jefa 3600 Nm (375 KgM) autopilot direct drive unit type DD2
The Jefa direct drive is one of the the strongest compact autopilot drives 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 40 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.

Output centre distance Offset distance Tiller centre distance
130 (standard lever) 106 200
165 (long lever, order special) 127 250
200 (extra long lever, order special) 162 307
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:

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 standard version has an output lever centre of 130 mm to work with 200 mm tiller centres. A long version of the output lever is available to work with 2500 and 307 mm centres (please specify on order).

 

The construction

 

The above assembly drawing shows a cross section of the direct drive. The drive can be separated in 4 main parts: The electric motor (1), the three stage planetary gearbox (2) and the electro-magnetic clutch (3) and the 1:5 spur reduction gearbox (4). 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.
  • 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).
  • 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 (1.4 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. 

DD2-12 volts performance table:
rudder torque
full rudder
(KgM)
rudder torque
midships
(KgM)
power
usage
(amps)
rudder rotation
per second
(degrees/sec.)
time for
72° rudder
(sec)
0 (no load) 0 0.5 6.7 11
120 60 6 4.9 15
180 90 9 4.4 17
300 150 15 3.2 23
360 180 18 2.6 28
480 240 24 1.3 55
DD2-24 volts performance table:
rudder torque
full rudder
(KgM)
rudder torque
midships
(KgM)
power
usage
(amps)
rudder rotation
per second
(degrees/sec.)
time for
72° rudder
(sec)
0 (no load) 0 0.2 5.2 14
180 90 4 4.7 15
360 180 8 4.1 18
480 240 11 3.7 20

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 DD2 direct drive in combination with various autopilot junction boxes.
Autopilot junction box 12 Volt version. Max. output (Amp.) Rudder torque midships (KgM) Rudder torque full rudder (KgM)
Garmin GHP12 sailboat APS (*1) 40 200 400
Simrad AC12 too small, don't use in combination with this drive
Simrad AC42 30 200 400
Raymarine ACU-200 (*2) too small, don't use in combination with this drive
Raymarine ACU-400 (*2) 30 200 400
NKE gyropilot 2 RVP (*3) 25 200 400
Furuno Navpilot not advisable due to lack in speed control and dynamic braking see this page
B&G H5000 Pilot (*4) 30 200 400
B&G Triton Pilot - High Current same as Simrad AC42 - see above
(*1) A special Garmin version of the direct drive is available under code number DU-DD2-12/GA. The Garmin rudder feedback unit is integrated and special Garmin cables and plugs are wired to the drive unit.
(*2) An internal rudder feedback unit is available for this pilot which saves installation time and a separate fundament for the external rudder feedback is not required. See below pricelist for the surcharge.
(*3) Please read the special installation instructions for the clutch available on our FTP server via this direct link.
(*4) From software release 1.1.84 onwards. Older H5000 pilots should be software upgraded. For a complete list of compatible B&G autopilots please follow this link.
Compatibility in 24 Volts.
Following table shows the maximum rudder torques at midships and full rudder that can be generated by the Jefa DD2 direct drive in combination with various autopilot junction boxes.
Autopilot junction box 24 Volt version. Max. output (Amp.) Rudder torque midships (KgM) Rudder torque full rudder (KgM)
Garmin GHP12 sailboat APS (*1) 40 200 400
Simrad AC12 12 200 400
Simrad AC42 30 200 400
Raymarine ACU-200 (*2) 15 200 400
Raymarine ACU-400 (*2) 30 200 400
Furuno Navpilot not advisable due to lack in speed control and dynamic braking see this page
B&G H5000 Pilot (*3) 30 200 400
B&G Triton Pilot - Low Current same as Simrad AC12 - see above
B&G Triton Pilot - High Current same as Simrad AC42 - see above
(*1) A special Garmin version of the direct drive is available under code number DU-DD2-24/GA. The Garmin rudder feedback unit is integrated and special Garmin cables and plugs are wired to the drive unit.
(*2) An internal rudder feedback unit is available for this pilot which saves installation time and a separate fundament for the external rudder feedback is not required. See below pricelist for the surcharge.
(*3) From software release 1.1.84 onwards. Older H5000 pilots should be software upgraded. For a complete list of compatible B&G autopilots please follow this link.

Pricing

Jefa direct drive units type 2

Part No.

Description

Price in Euro

DU-DD2-12

Direct drive 375 KgM type 2 12 Volts

€ 2.768

DU-DD2-12/GA

Direct drive 375 KgM type 2 12 Volts, incl. Garmin rudder feedback and cables

€ 2.999

DU-DD2-24

Direct drive 375 KgM type 2 24 Volts

€ 3.525

DU-DD2-24/GA

Direct drive 375 KgM type 2 24 Volts, incl. Garmin rudder feedback and cables

€ 3.759

DU-TS-RFB1

integrated rudder feedback unit for Garmin and NKE autopilots (10 kΩ)

€ 180

DU-TS-RFB2

integrated rudder feedback unit for Raymarine autopilots (5 kΩ)

€ 180

DU-TS-RFB3

integrated rudder feedback unit for B&G (NAC-2) autopilots (5 kΩ)

€ 180
The direct drive comes standard with the short output lever and should be completed with a draglink, a tiller pin and in some cases a tillerarm.

Service information:
Please click the left picture to open the DD2 folder on our ftp server for the explosion drawings and parts lists.