Rotation of the payload around its Z axis

This days I've been studying a little more in detail how to work on the rotation of the payload on itself, around the Z axis. The goal is to enable a rotation "in the air" in order to keep a steady heading (head lock).

Using Ardupilot Mega v2, it is possible to program a head lock using a software on the PC and using the mavlink protocol. So at this point, I am not too worried about programming a head lock.

The problem I was studying was rather : how to garanty that the servo is fast and robust enough to compensate a 60hz rotation during a 4 hours flight, while the payload is 2kg heavy.

The goal was to garanty that the servo wasn't the component undergoing the weight of the payload.

I came up with the idea of using a lazy susan that would be the connection between the balloon and and the payload (this is the piece thanks to which I have a free Z rotation non motorised)

Then, I need to have a rotation that can be controlled by the APMv2 board.

I found very interesting products on servocity. They have plenty of solutions for this kind of heavy duty activity. The schema below shows the whole mechanism.

Below is the a list of servos I am considering.

$60

$160

$60

All this equipments come from servocity. I still have to finalize my choice between the one that best fits my needs. 

I will be assembling it using the following lazy susan : 

It comes also from servocity (but can be found about anywhere on the web. At the time of writing, it's about $7