The point is, though, that to track a slow-moving target, the pod has a choice of using the outer, coarse gimbals, or the inner, fine gimbals or mirrors.
A sensible algorithm would use the outer gimbals to bring the target with a fine positioning window and then use the fine gimbals/mirrors to track it inside that window, and during that the outer gimbals would not move.
So an object moving slowly across the ATFLIR's vision would
a) initially be acquired by the outer gimbal,
b) then tracked by the inner gimbal/mirror to a set offset from the center,
c) re-centered via the outer gimbal,
d) tracked across by the inner gimbal/mirror to the set offset,
and so forth.
The fact that the inner gimbal/mirror exists means that the outer, coarse gimbal does NOT need to move continuously when tracking an object that exhibits "gentle motion" across the field of view.
I kind of agree with all your points from a) to d) there Mendel.
Though I think I disagree with what that means in reality.
I imagine ( again, no expert ) that the outer main gimbal would be in constant motion for all exercises except something which remained locked in one position. It must do.
If we are to imagine that the pod in mid field view has a window of , say 1 deg. ( I think someone, possibly Mick, has stated the deg field of view for this atflir, but let's imagine 1 deg.
The pod aims at that space in sky and then inner finer gimballed mirrors , which require minute movements within that window to track an object, take over.
These finer mirrors must be pointed at the correct part of sky to track, they are bound by the field of view.
In the gimbal footage the object tracks from 54 deg left and couple deg below, right across the nose. This is a massive amount of sky that it passes through which would require the gimbal to rotate very slow and steady constantly whilst the internal mirrors keep track within that field of view.
Mick, or anyone else can test this if they have a gimballed device, like the flir in Micks videos.
1) Attach device to chest ( or any motion less object ) with its base against chest so pointing out like an atflir.
2) Stick a laser pen on front lense to denote it's line of sight.
3) Moving the pod using it's bound 2 axis of rotate and pivot- track an imaginary line across a wall 54 deg left and a few deg below horizon.
It becomes immediately obvious that the pod must be constantly finely rotated with slight pitching all the way. Once it gets to centre, rather than a flipping of the pod, it merely must continue the rotation but apply an opposite, mirrored pivot to follow it the other side. It cannot do any other combination of movement and remain on track, it is bound to this motion if it wishes to remain on target path. It's also the easiest position to remain in against a target trying its best to evade. The on board algorithm would be designed so as to remain at certain angles at any given time whilst tracking an object - dependent on its current trajectory.
I believe that the 0 deg point of gimbal lock ( described as an undesirable state by Raytheon ) is not a set position in front of plane but a point in relation to trajectory of object which lies directly along its pivot axis.
If it allowed an object to track straight along this line whilst only pivoting, it could lose lock easiest if object suddenly banked. The pivot point would always be at , say 45 deg from the line of predicted trajectory so that any sudden change could easily be countered by slight rotation.
I will try and do some drawings to explain this better but if we imagine an object tracks straight and level left to right. If the pod followed it by having the pod merely pivot in line with object without any required rotation- this could lead to sudden loss of track if the object suddenly moved up or down. The pod would have to rotate a larger amount and pivot to regain. Whereas if it remained at 45 ish deg, any sudden change is covered by slight rotation. It has its bases covered so to speak.
Very difficult to explain so apologies if not clear. Will try and do a brief drawing when I have time to better explain my thought.