Answered: VEX U-Custom Internal Gears <R15iii>

Hey Karthik, is it legal to make custom internal gears for Vex U using the legal materials (3d printed plastic, aluminum/steel sheet, plastic sheet, plastic block)? Does this also extend to the replacement of the 11-48 and 12-49 gears accessable through the green back plate?

According to

from this Q&A, you may put “something else” in place of the standard gear
Q&A from Skyrise: https://vexforum.com/t/answered-vex-u-internal-motor-gearing/27350/1
from this Q&A, you may build off the motor housing as long as it’s solely a mechanical change
https://vexforum.com/t/answered-vex-u-removing-motors-from-housings/29776/1

if it is illegal to make custom internal gears, can you replace the green back plate of the motor and connect custom gears and mounts to the motor pinion?

Yes, this would be legal, provided that no other rules are violated in the process.