hello everyone. ive just recently started mountain biking so I purchased a 21 speed genesis terrain. I will say I don't have my experience on bike maintenance but I have about 200 miles on it so far and I was having trouble adjusting my rear derailleur so I purchased a new one. as I was attempting to adjust it I noticed my rear axle was bent so I purchased a new one as well. well I mounted and adjusted everything and took it for a ride today. but only after 2 miles my bike started making a lot of clacking noises. after looking at everything I noticed my axle was bent again. I did some research and from what I gathered was that a freewheel was prone to bending the axles very easily so it was suggested that I switch to a cassette. if I change to a cassette do I have to change anything else on my bike to accommodate this change?