I have a quad copter and I'm developing my own flight controller to run the code and testing it on the quad. As you all must be knowing, this means a lot of broken propellers. I thought of making a frame with prop protection but fabrication seemed difficult because 3d printing is proving expensive and cutting aluminum isn't that practical. Can you suggest a better way to fabricate?
It seems odd to me that cutting aluminum is cheaper than 3d printing plastic protections. As pointed out by @st2000, propeller protectors are available on the market, provided that you have a standard structure and propeller size.
Otherwise I would suggest that you look into polystyrene block to do your own propeller guard. This is a lightweight and cheap option.
Be aware that if you make your protection too big you will impact the aerodynamic of the airflow. This can be used as in ducted fan setups.