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B&G Pilot rudder position calibration

Discussion in 'Boat Electronics' started by Larry W4CSC, Apr 26, 2005.

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  1. Larry W4CSC

    Larry W4CSC Guest

    "Lionheart" has a B&G Pilot autopilot with electro-hydraulic (the blue one,
    RAM-T1-12V) ram directly on her rudder bellcrank. The rudder position
    sensor to feedback to the computer box is the Linear Feedback Unit strapped
    to the side of the ram cylinder.

    During the preflight checkout for our recent trip, I couldn't get the Pilot
    display to show the proper position of the rudder when I turned the wheel
    over by hand, stop to stop. After unloading the captain's stuff from over
    the rudder post, I noted the strap holding the linear actuator (crappy hose
    clamps) to the ram cylinder was loose and the mounting block that holds the
    linear feedback unit off the ram had moved. Simply tightening it back
    won't fix it. You need to do a cal on the linear feedback unit that's NOT
    in the manual or commissioning manual. A call to B&G's NEW Clearwater
    number (727) 540 0229 got great response and instructions I'd like to pass
    on here....

    To calibrate the linear feedback unit, tighten it back on so it can't move
    with the grease fitting so you can lube it. Make sure it will not be
    pulled too far out or in when the rudder moves to its stops, which will
    destroy it of course. Set the rudder so the linear feedback unit is fully
    compressed (in). Loosen the locknut holding the end of the moving actuator
    rod to the rudder drive unit. We're going to be TURNING this linear
    feedback unit actuator rod after we get its wires loose from the Advanced
    Control Unit (ACU). Isn't this fun?

    Open the ACU (the computer box) and note the colors of the wires coming
    from the linear feedback unit do NOT match the colors marked on the holes
    they go into. (Red wire to Red, Black wire to Blue, White wire to Green,
    shield wire to grey on the end even though it doesn't say.) After making a
    little drawing so you can get them back, remove them all and pull the cable
    out where you can get to the wires. Go get your digital multimeter.

    Connect one of the DMM probes to white, the other to black. Set the DMM to
    read OHMS. If it doesn't autorange, we're going to be looking for 250-350
    ohms so set the appropriate range manually. Now, while someone at the
    linear feedback unit ROTATES (not plunges) the rod of it around on its
    loosened nut, you read the meter and stop them when the resistance between
    the black and white wires reads 250-350 ohms....which is 300 ohms there in
    the middle. Tighten down the locking nuts so the linear feedback unit rod
    cannot rotate on its own as it slides in and out. Of course, if the body
    of the LFU rotates, like ours did, that screws up this setting, also.

    Reinstall the wiring from the linear feedback unit into the Advanced
    Control Unit, making sure the right wires are in the right holes. This
    completes the MECHANICAL calibration of the linear feedback unit.

    Follow the instructions in the Commissioning Manual and recommission your
    Pilot as to Rudder End Stops, Rudder Midship and let the computer run the
    Rudder Hard Over Time test it does. Make sure you step through ALL THE
    SETUP FOR ALONGSIDE COMMISSIONING even if you don't change other settings
    as it won't store the new settings if you don't on ours.

    Oh, it's SO nice to see that rudder position display now running perfectly,
    again. "The Ghost", as we call the totally silent B&G Pilot on Lionheart,
    is back in, ah, even if the crew blew out the headsail in
    heavy seas/winds...(c; The old headsail finally bit the dust, her
    stitching just pulled apart. The cautious engineer (me) talked the captain
    into turning us back to port as there were just the two of us handling the
    41' ketch in heavy no position to change the headsail at sea in
    these waves!....We motored safely home...

    I printed out these instructions and pasted them into the commissioning
    manual on Lionheart for future reference. It'll come loose
    just know it....
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