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Old 23-01-2011, 08:42   #1
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Raytheon ST500 SailPilot Linear Drive Not Moving

I did something to mess up the Raytheon ST500 autopilot. The SailPilot Linear Drive arm is not moving in/out. The unit is clean, no obstructions and I can manually move the arm in/out of the shaft. I can hear the servo motor power on/off. If I engage the autopilot, do +10 or -10, the servo motor winds up. If I manually turn the boat 10 degrees, the servo motor stops. If I oversteer, the servo motor starts back up. Clearly the electronics are signaling the servo motor properly. This tells me the electronics, compass, wiring are fine.

It appears that this is a mechanical problem with the rod inside the SailPilot Linear Drive unit. It is as if the threaded shaft disconnected from the gear. Is there a way to reset or reengage this? What could I have done to cause this? How do I go about fixing?

Thank you - I can't believe I could do something that would cause this to fail.....
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Old 23-01-2011, 11:40   #2
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The compass tells it where to steer, but the clutch must be engaged to actually engage the shaft. If you engage it via the autopilot control and it still doesn't move the shaft, I suspect the electric clutch is your problem. It's a relatively simple thing similar to a car's air conditioning clutch.
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Old 23-01-2011, 13:12   #3
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Steve - Thanks for the suggestion. When engaging the autopilot, the motor runs and responds properly to the change in heading. I tend to agree that it is probably the clutch. If I take off the black plastic housing, I would expect to see the motor, clutch and shaft and gear assembly. Any technical diagrams? Is it possible that the clutch got stuck open. How do I fix the clutch?
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Old 23-01-2011, 15:01   #4
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Several years and one boat ago, I repaired my old Autohelm 5000 linear drive and several various other autopilots of other cruisers while we were cruising.
I don't have your particular unit. Can you post a photo of the drive?
I suspect either the clutch isn't getting power to engage, or the coil is burned out.
I'll bet heavily on the former.
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Old 23-01-2011, 17:34   #5
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I found this on the Raymarine site. I'll be checking the clutch.

Quote:
The autopilot drive unit contains a DC motor that is simply reversed by the change in output polarity from the course computer, the drive unit also contains an electromagnetic clutch that is controlled by the STANDBY/AUTO buttons. AUTO engages the clutch, STANDBY disengages it.

The clutch is basically a coil, which when energised, (by 12v regardless of whether the system is 12 or 24v), locks the epicyclic gears and enables drive from the motor to the rudder.

Check that when AUTO is pressed, 12v is present at the clutch wires (the two thin ones) next to the drive unit. If it is, check the clutch coil has engaged - either a 'clunk' will be heard from the drive unit or the drive will appear to 'lock up'. Make sure that when the clutch is engaged, the voltage does not drop below 11v, if there are high resistance connections in the clutch wiring this may cause the voltage to drop and the clutch may than only partially engage.

If the clutch does not appear to engage, it could be electrical, check the resistance of the coil - if open circuit or short circuit the coil will need to be replaced,( this may have also damaged the course computer too). If the fault is mechanical, for example, the clutch may engage, but could be slipping, the drive unit will need to be serviced.

If 12 volts is not present on the clutch wires, check the clutch output of the course computer, if 12 volts is not present here either, the computer will need to be serviced.
If you are certain the clutch is operating correctly, the other possibility is that the motor brushes may be dirty, worn or sticking, however in this case, you should find the steering is 'locked' by the clutch when AUTO is selected.
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Old 25-01-2011, 18:16   #6
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This is really strange. Before checking voltages for linear drive and clutch, I tried the ST5000+ autohelm - it worked fine. I suspect that the clutch was stuck open. For whatever reason, it now works. I guess I'll be watching for this to happen again.
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Old 25-01-2011, 21:03   #7
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Check for loose, corroded connections and plugs.
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Old 25-01-2011, 21:10   #8
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Does the pushrod pull all the way out? Not sure of the ST500. But whatever Raymarine tillerpilot I had the pushrod would sometimes come unscrewed from the ballscrew actuator inside - falling to the deck. It can be threaded back on. I used a tiny bit of thread locker to keep it there. The design is very poor...almost like nobody at Raymarine owns a boat
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Old 25-01-2011, 21:13   #9
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The other day, when the clutch didn't engage, I did pull the shaft out and push back in. It did stop at the ends. I optimistically thought it had reengaged, but it was wishful thinking. I'll check if the rod is unscrewed.

Agree on loose or corroded connections - I think this will be the cause for lots of problems.
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Old 25-01-2011, 21:17   #10
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...also the cheap plastic spur gear press-fit onto the motor shaft finally spun. That and the fact that they screwed the aluminum pushrod directly to the bronze ballscrew nut.....sheesh.....had they not heard of corrosion?
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