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Dream Maker · 30-10-2023, 20:10

Question: I am trying to figure out if the autopilot RFU remote feedback unit (the little piece of plastic that looks like a tiny rudder) is FREQUENCY or RESISTANCE based. (Never thought I'd be asking that question. LOL

Background: Our Navman / Northstar autopilot display failed. It cannot be repaired or replaced due to its age and the manufacturer being bought out and the new company not supporting the products.

We are looking to purchase a new autopilot brain and display. This will connect to our existing autopilot pump and linear drive as they are fine.

Garmin says we need to know if the Navman RFU is frequency or resistance based to know if the existing RFU will work with the new system. That little piece of plastic costs $500.

Our Navman manual does not include any info on the RFU and I haven’t found anything online. The boat is in a different country so I can't pop down and see if it will work.

Any advice would be much appreciated

FlyingScot · 30-10-2023, 20:52

I don't know the answer, but RFU normally refers to Rudder Feedback Unit.

stormalong · 31-10-2023, 00:01

Test it with an ohms function of a multimeter.

Does it have three wires? Yes=Probably resistance. Check the resistance between any two wires.

If the resistance is constant without moving the tiller arm it is a resistance sensor. If the ohms scale shows an open circuit or changes in value over time it is capacitance based.

For a resistive sensor the resistance across two of the wires will be constant with the movement of the tiller arm while the third wire to one of the other wires will change resistance. This is a simple variable resistor or potentiometer.

I have never heard of a frequency based rudder feedback unit. All that I have seen are resistance.