The original toy had 2 motors to control the gantry and a third to control the height of the grabbing claw. The gantry had limit switches on each of the sides. this was al controlled by three switches mounted on the front panel of the toy.
To interface the Raspberry Pi to this grabber machine, we need to control these three motors and use the 4 limit switches to move the gantry.WeI've used a L293 driver ic with 1 relay for each axis to switch over the limit switches for the gantry and a relay and transistor to control the grabber movement and direction. I could have used another L293 to do this, but I only had the one. The relays are all driven by transistors, some BC547s.
The limit switches were wired in series with the motors, these were swapped over by the relays depending on the direction of travel.