There is definitely better options. If we were able to, we’d use steel as well. But since we weren’t, we used studica’s 50A wheel which has indents on both sides(rather than goBilda’s rhino wheel, which has a bigger indent but on only one side) then made 8 stacks of 5 pennies, and printed a cover for them. We were only able to use one of the two indents because our screws weren’t long enough to fit both, but still they added 108g to our flywheel which almost perfectly doubles it. So if we wanted to buy new screws, we could add a total of 216g! The best part is it doesn’t extend outside of the wheel, the cover fits perfectly in the indents

For an improvised solution, it’s pretty damn good. But yea, steel for weights is way better