Subscribe to download
RotorAlign

for tunnel-boring trucks, etc.
basically keeps a rotor or hinge aligned so a remote control on the joint will have no roll, faces upright.
The PB with the script should be on the arm to be aligned, along with the remote, both on the rotor-part ('top') grid, so the rotor/hinge/advancedrotor itself should be on the parent grid, everything else on the child grid. Running the script manually will toggle its on/off state, so you can bind "run" with empty argument to the G toolbar to easily turn it on and off; just disabling the PB will leave rotor with whatever velocity script last instructed it to have, so is not a clean recommended way to turn off the aligning, so don't simply turn the PB off!
Multiple arms can be controlled separately, even in a chain, at risk of invoking Clang's wrath, but each joint of the arm currently requires its own script and blocks.
New feature:
If set remote's CustomData to "waypoint", will use direction to the remote's currently *active* named waypoint target instead of gravity up direction for alignment
new feature: if set remote's CustomData to a GPS location string of format "XXX:YYY:ZZZ" will do similar but for a custom target
example1
example2