This part holds the motors and the flywheels in place to make sure that it fires correctly and allows anyone to make a flywheel without expensive Motors.
DC Hobby Motor Type 130 Micro Motor:
https://www.amazon.ca/Gikfun-1V-6V-Hobby-Arduino-EK1894C/dp/B07BKXJM71?source=ps-sl-shoppingads-lpcontext&ref_=fplfs&psc=1&smid=A34K5WF5Z9R33P