What is presented is a mechanical arm assembly with a novel roller thrust bearing. The mechanical arm assembly comprises a first arm having a first end and a second end. A first roller thrust bearing is mounted to the first end and to a ceiling. A second roller thrust bearing mounted to the second end. Each roller thrust bearing comprises a first bearing body and a second bearing body able to rotate relative to each other. Each roller thrust bearing has a solenoid powered brake comprising two brake shoes each with a high friction brake pad mounted to a hinge body affixed to the first bearing body, a brake drum mounted to the second bearing body, a tension spring pushing the brake shoes against the brake drum, and a mechanism for disengaging the brake shoes from the brake drum. The mechanism comprises a slider body with space for two pins, two ball bearings, and a plunger with sloped surfaces on one end and a mounting provision on the other. A solenoid is attached to the mounting provision. The sloped surface is shaped such that when the solenoid is activated and the solenoid moves the plunger, the sloped surface pushes the ball bearings apart which pushes against the pins apart which in turn pushes against the brake shoes thereby disengaging the brake shoes from the brake drum and permitting the first bearing body to rotate relative to the second bearing body.