Reducers are a key component of the RR1 robot arm. I use my own custom built 3D-printed planetary gearboxes. The following video shows assembly of the gearbox for the upper joint (elbow join) for the second prototype of RR1 ("rev.2"). There are a total of 6 similar gearboxes of various sizes across the robot.

As the gearboxes in RR1 use herringbone gears for smoother rotation, the assembly must be carried out exactly as shown in the video. All gears must be meshed together well so that there is not much friction and not much backlash at the same time which is especially difficult to achieve with herringbone gears. The video shows that the assembled gearbox rotates smoothly and has no detectable backlash. Such an achievement requires lot of experience and a very good 3D printer (I use Prusa i3 MK3S+).

And as you can see "rev. 2" will be orange.