Awesome, awesome project! Thank you for sharing this! The main arm can be printed on the Qidi X-One's 150x150mm build platform, if you angle it up and diagonally. Takes a massive amount of support structure, but I didn't get into this hobby because I'm a cheapskate. I used 4ndreas's Mantis Gripper (https://www.thingiverse.com/thing:1480408) so the kids could feel like they they had a massive claw to wield. This requires an adapter, already designed by Runkel (https://www.thingiverse.com/thing:2410200). This gripper is heavy, so the arm usually falls downward when I power this down. Otherwise it's great.
I had to design a power enclosure (https://www.thingiverse.com/thing:2615944) that fit the power supply I already had, which is massive overkill (MeanWell RS-50-5). And also held the Arduino Uno, power bus, and joysticks. I left room for the guts of a 9v wall wart to power the Arduino separately. I was getting a lot of wierdo jitters and oddness when powering it from the MeanWell.
Arduino code to make the joysticks control the servos was found/modified from here: https://forum.arduino.cc/index.php?topic=239959.15 It was originally created to run a backhoe, so you'll see some interesting variable names ;)
Mantis Gripper by 4ndreas: https://www.thingiverse.com/thing:1480408
Mantis Adapter by Runkel: https://www.thingiverse.com/thing:2410200
MeanWell RS-50-5 Enclosure, etc. by me: https://www.thingiverse.com/thing:2615944
Most parts 100% for rigidity, large parts 25%