Sex and the Autopilot

[Joe Okros]

Got your attention!! I guess sex does sell, but seriously this is about mating autopilot bits, so it’s slightly relevant. And to be blunt they are both f!@#ed so I guess at some stage it must have been relevant

I have an old Cetec Benmar autopilot with the Cetec hydraulic pump, about 4 years ago it stopped working (went around in circles). I couldn’t find spares or much info about it, so I bought the Simrad wheel pilot which was pretty new at the time. This AP has steered the boat all the way from the Caribbean to New Zealand – not bad for a cheapie in my books. It has however in the process managed to chew through a few belts as well as the housing containing the belts and in now no longer operational.

Cut to the here and now. I have functional control unit, albeit for a wheel pilot and a functional hydraulic pump without a control unit. Now being in the land of the no8 wire, I am contemplating mating these two to get a functional unit. Has anyone done something similar? I know the main obstacle is probably the current draw of the pump (which I have not measured yet), but my poppa taught me it’s always better to learn from someone else’s mistakes. So if anyone has done something like this please let me know.

[44'cruisingcat]

It should work as long as it's a reversable pump, not a constant running one.

It's really a question of whether the control unit can provide enough amps to run the pump at full power. So it's possible it will be fine when things are smooth, but will lack grunt when it's required to do more. I'd try it.

[John A]

Borrowing from the second subject of your post, you may get unpredictable results. It has something to do with the number of chromosomes of the two units.
Please let us know so that we can see if your poppa was right.

[Sailmonkey]

even if the pump draws more amps than the wheel pilot can deliver, this can still work. Just buy a few of those 30amp relays (hella, radio shack...etc.) and use them to deliver the current to the pump. The voltage from the wp will control the relays.

[Joe Okros]

I'm not on the boat at the moment. How would I know whether the pump is reversing or continuous when I look at it---Amazing the response you get when you stick SEX in a post.

[Sailmonkey]

a constant running pump with a valve block will have more wires running to it. 2 wires to run the pump, and usually a minimum of three wires to direct the oil. 5 in total at a minimum. A reversible pump will have just the two wires. reverse the polarity and the oil moves the other direction. Either way I'm confident that if you can find all the needed wires to control this you can hook it up to the wheel pilot.......should be interesting.

[DeepFrz]

Instead of relays I would suggest a solid state drive unit between the controller and the pump. Many autopilot companies make these things. Check with the locals for a locally made autopilot and find out what they have.

[NoTies]

Short answer.Yes (assuming the pump is a reversible polarity type). Relays will prevent the control unit sensing helm load and response so don't use them. Simply wire the wheel drive wires to the pump. Don't use relays as they will prevent the control unit sensing helm load etc. I went through this exercise converting a Raymairine ST3000 wheel pilot to Octopus hydraulic drive. Raymarine said it couldn't be done so, being a Kiwi, I went and did it anyway. Electrical load (start up & running current) were less than the wheel drive. Best response pilot I have ever had.

[Joe Okros]

Took a look at the pump yesterday. It consists of a separate electric motor driving a pump by what I assume to be a belt - cant see as its enclosed. It has 12 volts wired to a box that appears to be a control unit mounted on the pump unit as well as a cable containing multiple wires going into this control unit. This is labled PHC and I assume it comes from the autopilot controller. The pump has three hydraulic lines coming from it, so I assume its reversible. I will have to open up the control unit on the the pump to see what it does and trace the wiring back to the autopilot controller unit. I suspect attaching the wires from the wheelpilot that turned the wheelpilot motor to the appropriate places on this pump control panel will make it work. I am a bit concerned that it has 12V permanently wired to it, as that would indicate more "brainpower" in the pump control unit than I would have presumed. I will know more when I open that pump unit control located on the pump. Does anyone have any experience with these BENMAR hydraulic pumps?

[sandy daugherty]

So now you know the downside of combining sex with an autopilot: interest expires soon after a brief flurry of activity.

[Joe Okros]

yeah well, a little bit is better than nothing at all, or so my "shorter" friends tell me.

[Stein]

Ha ha!

I've never tried anything similar to this mating of different AP systems, but my guess is that if you can make it so that the Simrad "brain" does all of the "thinking", and let it get direct access to the motor control, this should work. I would guess the electric motor running a smooth geared down hydraulic pump, will draw quite a bit less current than the wheel drive unit.

I've witnessed a number of wheel and tiller pilots give up way before they should. Controlling multis by belts and servos is apparently no good idea. The present hydraulic AP has way more grunt, makes way less noise, never fails (several years of heavy usage) and loads the batteries about half as much. But also costs WAY more. Seems like the high purcase of the hydraulic system makes it operate entirely in its low load region.

Stein

[John A]

The main problem of two dissimiler units is the timing and sigmal strength between the control unit and the "brains" or computer. On most things computer driven, even the length of the cable/wire can influnce the amount of time taken for an electric impluse to travel between two units. If the expected cycle of electricity is late, the computer goes crazy.

.

[Joe Okros]

Well, I eventually got rid of enough other jobs to do this one. I connected the wires of my reversing pump to the wires that drive the wheelpilot motor. It would seem the wheelpilot is a stepper motor that obviates the need for a rudder sensor. Unfortunately it overdrives my reversing pump causing it to make such big course changes that no amount of playing with gain and seastate settings make much difference. The only way this can be overcome in my opinion is with a Rudder position sensor connected to the Wheelpilot. Unfortunately I have no idea whether connecting a new Simrad RPS to the Simrad WP32 will work and am loath to spend the money,---any ideas?

[goboatingnow]

Originally Posted by Joe Okros

Well, I eventually got rid of enough other jobs to do this one. I connected the wires of my reversing pump to the wires that drive the wheelpilot motor. It would seem the wheelpilot is a stepper motor that obviates the need for a rudder sensor. Unfortunately it overdrives my reversing pump causing it to make such big course changes that no amount of playing with gain and seastate settings make much difference. The only way this can be overcome in my opinion is with a Rudder position sensor connected to the Wheelpilot. Unfortunately I have no idea whether connecting a new Simrad RPS to the Simrad WP32 will work and am loath to spend the money,---any ideas?

I was about to post this, you have a problem, most modern wheel pilots don't have facilities for external rudder feedback, hence you have a fundamental problem of how to close the feed back loop. If its a stepper motor drive then it's will not drive a conventional permanent magnet drive motor properly at all.

Forget it.

Dave