There are of course, three sides to every story, but that's for the OP to weigh in his own mind.
Josh - consider this advice. In every situation try to "think like your adversary." You can dwell on what you want and just spin your wheels, however, your problem solving skills will be greatly enhanced by trying to figure out what is motivating your mother and step father. "What's in it for them?" How are their lives enriched by me not being involved in this hobby?" "How do they think my life will be enriched by me not being in this hobby?' "What is their agenda?" "What are they trying to achieve?"
I've read some comments directed to you in this thread and your responses are emotional and abrupt "No! They HATE it!"
I read your quick dismissal of playing sports - "I can't play sports - I have flat feet."
This is Dustin Carter - a high school wrestler from Ohio. He has no legs, no hands, no forearms and he not only made his high school wrestling team but advanced to the second round of the state finals beating hundreds of other competitors.
This is Jim Abbot. He was born without a right hand. He played ten years in the major leagues and in 1993 pitched a no hitter while playing for the New York Yankees.
Point being, you can do pretty much anything you want to do.
You had an incident with your mother and step father and you came here to blow off steam and you want people to take your side because in the near term, that is going to make you feel better. While it's a quick fix, and you probably do feel better, it's not a long term solution.
Be honest with yourself. Is it possible your mother and step father are disapproving of your hobby because you neglect other aspects of your life, or certain responsibilities. Do you have chores they have to tell you to do ten times because you're always in the train space? Are you excelling in school, or lagging behind because you spend a lot of time on your hobby?
Whatever it is, they have an agenda. Whatever that agenda might be, it isn't for you to be unhappy. When your parents tell you they're doing something for your own good - if they're good parents - they really are doing it for your own good.
Generally, if there is one thing every parent wants, it is to steer their children away from making the same mistakes they did when they were the same age as their own child. Parents want children to be prepared for the world, to not squander opportunity or not realize their potential. Every parent failed to do something in their childhood which has impacted what they achieved in life. Those same parents want to keep their own children from making the same mistakes.
One thing about parents and adults in general, as much as you may hate to admit it - they're smarter than you. They know more and they have three or four times the life experience you have. This is a valuable exercise for learning to problem solve in life. Look at it with an open mind and figure it out. You'll be a better person with more opportunities for future success because of it.