So for my FASBot, I decided to use this electric screwdriver with a nut driver attachment to performing my fastening. This is my machine's "spindle", though I've modified it in order to better fit into my machine. First, to reverse-engineer it!
The whole thing comes apart in four pieces. One piece, the black one to the left, contains the tool holder and a planetary gearbox. In the middle, an orange housing separates into two halves, which houses the drive motor, a triggering mechanism, and the detachable battery pack. Because my machine will have its own power, I can chuck the batteries, which eliminates the need for about half of the orange housing.
These pins press into the orange housing sides and force the two halves to mate.
A flexure provides the electrical contacts between the battery pack and the trigger mechanism on the rear side of the motor.
Flexures also keep the battery pack attached to the orange housing. Press both ends in, and the battery pack detaches. Push the battery pack back into the orange housing and it'll click into place.
The sun gear of the first stage in the planetary geartrain is attached to the motor shaft. You can see plenty of lubrication inside where the plastic gears live.
You can see here the U-shaped pin that passes through two holes that go through the black gear housing and the orange housing, to couple the two together.
This is the trigger mechanism in back of the motor. Push the trigger down, the motor spins one way. Push the trigger up and the motor spins the other. I looked into the mechanism and saw that there are flexural electrical contacts, one power, one ground, that the trigger interchangeably applies to the motor terminals to change the motor spin direction.
Very cool! I will design a custom piece that holds the motor and mates with the black gearbox housing.