Depending on your motor, this step may be either simple or very complicated. Generally, you need to make two or four holes at the edge of your frame. That or has a reason to exist.
Some market frames look like this:
These have all the necessary holes that you may need, assuming that your motor has normal dimensions. So, there is nothing more to do than taking a screwdriver and placing some screws over the four motors.
But if you try to mount your motors in wood, aluminium, or some other material that has no holes, you will have to do some more work. Almost all the motors have some specifications on the market from which you have bought them, as shown in the following figure:
So, hopefully, you can find the dimensions of the motors and the exact size and spacing of the holes needed. Either you can make some holes with appropriate tools or buy an external motor mount system, as shown in the following image. The motors usually...