We still have the original little banebots motor driving the arm of our 2007 robot. It's a long arm on that robot, too. We used a gas spring.
This year we're using a single window motor to raise the arm...it's also a long arm.
Here's the lower attaching point for our passive assistance--easy to adjust, just push it up or down the pole, it stays where you put it, because of the magic of friction and leverage.
Great post JVN! as usual