My autopilot is a windscreen wiper!

[Tim Good]

Ok so I finally managed to extract my faulty autopilot from my pedestal. It is enclosed within so getting at it is tricky. Now I've finally done it I was shocked how small it was. On googling the part number printed on it, it appears to be a German made windscreen wiper motor. This one:

http://www.smolka-berlin.de/onlines...EC_ITT_403.929_gear_motor_12_V_TYP:_SW2K/4921

Is this normal or has the previous owner thought he'd save a bob or two? Note that it is on a 43ft, 20t boat!

 

[William_H]

I would not find that surprising that the original maufacturer of the a/p found that they could get a suitable motor and gear box from an auto parts supplier. Cheaper and better than making his own. Presumably the power from the wiper motor was adequate. If the motor has gone bad then you may be able to find a repalcement cheaply. good luck olewill

 

[Norman_E]

With torque of only 2 newton metres (just under 1.5 foot pounds force) it does seem a bit low powered for an autopilot drive on a 20 to boat unless it is further geared down. Has the autopilot performed OK in the past or did it regularly fail to have enough grunt? If the latter you should consider what current the course computer can handle, and choose a more powerful drive if possible. A few years ago a lot of autopilots were a bit low powered by current standards, for example my Simrad AP11 with the 3000 course computer can only handle a drive unit drawing less that 10 amps maximum, and the actual electro mechanical linear drive is actually rated at 5 amps, though it may peak close to 10 when at its limit. If I don't balance the sail trim reasonably well it can let me know by giving up and sounding the drive failure alarm.

EDIT. I am a bit surprised that a 20 ton boat has a drive working in the steering pedestal. A linear drive acting directly on the steering quadrant is more usual on such a boat, and probably a better arrangement.

 

[elton]

I would expect them to source the motor from an off-the-shelf source, rather than having one custom made. They can achieve remarkably high torque and low speed, without reduction gearing, by driving a small motor with pulsed current, (ie a 12V square wave) which is just what's needed in an autopilot.

 

[Tim Good]

With torque of only 2 newton metres (just under 1.5 foot pounds force) it does seem a bit low powered for an autopilot drive on a 20 to boat unless it is further geared down.

It is geared down via in a couple of places within the pedestal but I'd have though all chain drive systems would be surely?

I am a bit surprised that a 20 ton boat has a drive working in the steering pedestal. A linear drive acting directly on the steering quadrant is more usual on such a boat, and probably a better arrangement.

Yes I agree. There is a arrangement for doing that on my boat as there was once an old hydraulic linear drive from an old Wind Hunter System. Providing the Autohelm computer outputs the right voltage and signal it might be an easy swap.

They can achieve remarkably high torque and low speed, without reduction gearing, by driving a small motor with pulsed current, (ie a 12V square wave) which is just what's needed in an autopilot.

When I took a multimeter to the output of the AutoHelm computer it was giving 7V +/- outputs. Does that sound right? The drive unit is definitely rated at 12v.

 

[elton]

When I took a multimeter to the output of the AutoHelm computer it was giving 7V +/- outputs. Does that sound right? The drive unit is definitely rated at 12v.

An oscilloscope would yield a lot more information about it than a multimeter, such as the pulse width, pulse frequency, mark-to-space ratio, as well as the pulse voltage. Depending on what type of multimeter, it will probably show the averaged voltage over 10s or 100s of milliseconds, and 7V is a typical voltage, though it may be greater or less, dependent upon load and required course correction.

 

[Norman_E]

Is it actually a pulsed output? My Simrad Robertson course computer simply delivers a bi-directional 12 volt supply so that the linear drive can push the quadrant to right or left as needed. The rudder feedback device tells it when to stop. The obvious question is, does the OP's boat have a rudder angle feedback device connected electrically to the course computer?

 

[Tim Good]

Is it actually a pulsed output? My Simrad Robertson course computer simply delivers a bi-directional 12 volt supply so that the linear drive can push the quadrant to right or left as needed. The rudder feedback device tells it when to stop. The obvious question is, does the OP's boat have a rudder angle feedback device connected electrically to the course computer?

Yes there is a rudder reference device. See the diagram below. Click for larger image.

I understood it would be bidirectional 12V also. I.e. the motor is either turning one way, not turning or turning the other way. That's all. Or at least thats what I thought the course computer would be doing.

Bigger picture: