M1A2 SEP lead acting up randomly.

[Assassin 7]

So I did some tests while on the move, randomly shots are extremely off. I also noticed that when you stop just after a lase you shot will miss. This happens between 2 to 3 seconds which i havent move my control handles and the gun should stay alined with the LOS of the sight almost instantly unless a fast Turret slew is happening. Its not many rounds doing this but there are some, I had 5 do it during this test session.

 

 

[Assassin 7]

Here is the scenario: 

 

 

M1a2 Lead test.sce

[Ssnake]

Okay, so just that we're on the same page. Fire Control Systems may sometimes behave slightly unexpected in certain extreme cases.

 

The way I understand it, the M1 does not make a distinction whether the turret's turn rate is caused by the own platform's movement, or the target's movement, or both. They get conflated into a single lead angle. (Contrast this with the Leopard 2's concept of the Backsteering/negative feedback to compensate for the own platform's lateral movement, or the fact that you're supposed to press dynamic lead only if the target is, in fact, moving (otherwise: Leave it off)).

So, if there is a rapid change in the tank's own movement and if that rapid change happens in a shorter duration than the moving average of the turret's turn rate sampling there could be deviations that result in a miss. Not saying that this is exactly what happens here, but I'd like to rule it out before sending the programmers on a wild goose chase.

 

Another question would be how long, exactly, the sample for the moving average calculations really is in the M1A2 - 1.5 seconds? two? 2.5?

Our sample rate is higher (=every frame, I believe) which should actually result in a better quality overall, so we need to make sure that the sample duration is correct. Even then, if the tank comes to a full stop in a second and if the sample duration is 1.5 seconds, you'd still have a third of the sample with the tank moving at full speed, and two thirds of the sample with the tank moving at half speed, and only the newest samples will have "zero" as the own platform's movement rate.

 

So this is what we need to disseminate before we can decide that something's really wrong, and if so, what needs to be done to fix it. If you could help us with that, that would be super.

[Assassin 7]

16 minutes ago, Ssnake said:

Okay, so just that we're on the same page. Fire Control Systems may sometimes behave slightly unexpected in certain extreme cases.

 

The way I understand it, the M1 does not make a distinction whether the turret's turn rate is cased by the own platform's movement, or the target's movement, or both. They get conflated into a single lead angle. (Contrast this with the Leopard 2's concept of the Backsteering/negative feedback to compensate for the own platform's lateral movement, or the fact that you're supposed to press dynamic lead only if the target is, in fact, moving (otherwise: Leave it off)).

So, if there is a rapid change in the tank's own movement and if that rapid change happens in a shorter duration than the moving average of the turret's turn rate sampling there could be deviations that result in a miss. Not saying that this is exactly what happens here, but I'd like to rule it out before sending the programmers on a wild goose chase.

 

Another question would be how long, exactly, the sample for the moving average calculations really is in the M1A2 - 1.5 seconds? two? 2.5?

Our sample rate is higher (=every frame, I believe) which should actually result in a better quality overall, so we need to make sure that the sample duration is correct. Even then, if the tank comes to a full stop in a second and if the sample duration is 1.5 seconds, you still have a third of the sample with the tank moving at full speed, and two thirds of the sample with the tank moving at half speed, and only the newest samples will have "zero" as the own platform's movement rate.

 

So this is what we need to disseminate before we can decide that something's really wrong, and if so, what needs to be done to fix it. If you could help us with that, that would be super.

Sure, will contact you soon by email. 

[Ssnake]

Yes...

[Ssnake]

From what I'm seeing in the video, the lead isn't technically "acting up" but behaving as designed; maybe that design is slightly wrong if the M1A2 SEP received a fire control system upgrade to include the equivalent of backsteering (as your email suggests), but given a 1.5 seconds sampling duration, stopping the vehicle from full speed within that sample duration must deliver the kind of deviations observed (except maybe that one freak shot in the middle of the video). Say you have a sample rate of 5Hz, a sample duration of 1.5 seconds, you'll get 8 samples where the own vehicle speed enters the ballistic computations like this (I'm going by reducing energy from the moving vehicle at a constant rate, not velocity),

 

Sample 1: 40.0 kph

Sample 2: 37.4 kph

Sample 3: 34.6 kph

Sample 4: 31.6 kph

Sample 5: 28.3 kph

Sample 6: 24.4 kph

Sample 7: 20.0 kph

Sample 8: 14.1 kph

Sample 9:   0.0 kph

 

Average of samples 1...8 = 230.4 : 8 = 28.8 kph. This assumes the own platform comes to a full stop just before the 9th sample displaces Sample 1 in the calculation of the moving average) when you fire. Even with backsteering added to increase overall precision, as long as you build a moving average of 1.5 seconds there will always be a 1.5 seconds delay before the moving average is clear of non-zero velocity movement (and thus of turret angular motion to compensate for it since, technically, we're measuring samples of the turret turn rate here; I used velocities for simplicity, just to illustrate the principle).

With samples 10+ all being zero, of course the calculated average quickly drops off to 23.8 kph, 19.1, 14.8, 10.9, 7.3, 4.3, 1.8, 0, 0, 0, ...

 

Now, if the sample duration were not to be 1.5 seconds, or if the vehicle velocity isn't part of a moving average calculation, the picture changes of course. That's why I'm asking for such details.

[Ssnake]

Okay, I took what I could from what you sent and made that report #8074.

[Assassin 7]

Thank you sir