Electronic – Powering Two Motors through a Three Conductor Cable

One important factor when working with stepper motors is hold torque. You can do some simple calculations based on your camera weight and platform radius to determine the torque due to gravity, and your hold torque should be a fair about larger than that or the motor will slip. You'll also need stepper motor drivers in order to control the motors and provide enough current as well as the proper signal to control the motor. I've had experience with the Pololu A4988 I'm conjunction with Arduino; it's simple to use and only used 2 digital IO pins (at minimum). You can also spare more pins and control things like the driver enable, etc. As for actually choosing a motor, that can be tough. I'd pick a price range and form factor that you'd like to be within and use that to narrow it down. I'd also stay away from the spark fun motors as they are usually on the more expensive end and not the best bang for the buck.

You are comparing potatoes and apples. The limits of stepper motors are known, while you are comparing servo motors, which indeed are RC servos, not the PMSM or BLD servos. In the link you can see BLDC motors. Now it is up to you to choose a BLDC or PMSM motor and driver. The you' ll need a master controller, which will send position setpoint with known speed, acceleration - aka trajectory generator. Each driver has to correct the actual position vs. setpoint position with the use of cascaded control loops - position, velocity, current loops.

This cascaded controll loop has also feedforward paths, like setpoint velocity from trajectory planer is fed forward to the velocity loop, regardeless what is the position error. In the same manner you have a torque/current feedforward path, derived from velocity setpoint. The required feedforward torque is: \$ T= J\cdot\alpha\$, where \$J\$ is the moment of inertia of the system: motor's rotor inertia + transformed inertia of the load. \$\alpha\$ is the angular acceleration \$\alpha=\dfrac{d\Omega}{dt}\$, where \$\Omega\$ is the velocity setpoint. A high end servo is updating the current controller at aprox. 50 micro seconds, the velocity controller at 100 micro seconds, and the position controller at 500 micro seconds or more, it depends on the trajectroy planner.