Replacing the Rudder Reference Unit (RRU)
For years, my B&G ACP2 autopilot had a difficult time holding a straight heading. The autopilot "brain" has a couple of parameters you can "tune" to get the autopilot to change its course smoothly and without overshooting. Over the course of countless hours playing with it, I explored the entire 2-D parameter space, yet the best I could get is a course that weaved through 6-8 degrees, over 10-12 seconds.
I was finally able to track the problem to a faulty linear Rudder Reference Unit (RRU). This is a long tube that is mounted above the T2 autopilot ram, and is used to indicate the rudder position. Mine had a big flat spot. The rudder could change a couple of degrees, yet the RRU would indicate ... nothing. No wonder it weaved!
I bought a new RRU from Wheelhouse Marketing (954-229-2460), a B&G representative located in Florida, and got it a few days later.
Unfortunately, it was considerably different from my old unit: more slender, and much longer.
Here's what it looked like when I was done.
The T-2 ram with the new linear Rudder Reference Unit on top. A piece of HDPE holds the body of the RRU, and a small piece of stainless holds the slider.
Detail showing the HDPE that holds the body of the RRU. There's a slight gap (barely visible in the picture) that closes up when you tighten the bolts, firmly holding the RRU.
Detail of the piece of stainless that holds the slider.
Unfortunately, when I put everything back in the boat, I kept getting a "Fault 111." According to the manual, this error means
The current limit circuit for the drive motor (25 amps) or the clutch (2 amps) has tripped.
I measured the current for each circuit. The current flowing through the "clutch" (it's actually a solenoid that bypasses the hydraulic circuit) looked normal (about an amp), but the motor showed spikes well over 20+ amps. My theory was that taking out the ram shook some carbon lose from the brushes, causing it to short out the motor's commutator.
Taking one of these things apart turns out to be surprisingly easy.
To get at the electric motor inside the ram, undo the two bolts on the end cap.
Slide the motor casing off the ram, then tap off the end cap using a drift punch.
The motor casing with the end cap removed.
Taking off the motor casing reveals the electric motor inside. It's in surprisingly good shape, with very little evidence of corrosion.
Once apart, there was a lot of dust inside the motor, so it's not surprising there could have been a short. Using a utility knife I cleaned the gaps between the segments of the commutator. I also cleaned the windings and inside of the case using compressed air and rags.
Don't forget to put the compression spring in before putting the end cap back on!
I put everything back together, then reinstalled the ram. To my amazement, it worked. It's rare for a boat project to go so well!
The autopilot ram, back in its natural habitat.