0.21 SAS Test

[Sardonyx]

I did a couple tests of SAS in 0.21 to see how it performs during rocket launch. Here's my results with videos.

Test 1: Normal launch of the craft. SAS is enabled from launch. There are 6 reaction wheels, one at the top of each booster under the nose cones. In this test SAS is able to keep the craft on course. I keep the last set of boosters in place to destabilize the craft somewhat in the roll dimension. There is no input from me other than the gravity turn. Note that SAS is using some Roll correction to keep the craft stable.

http://youtu.be/JXINZ7P6W6k

Test 2: This didn't go as intended. It's similar to Test 1 except the booster separation stage goes poorly. When the second stage of boosters disconnects, it damages a remaining booster sending the craft into a spin and ultimately causing it to break up. I let the flight continue to see if SAS would correct the spin. Initially it does. However after the spin is damped, it continues to applies a massive over correction reversing the spin. I've developed simulators similar to this (ground vehicles) before, also using PID controllers to control HPR. I'm wondering if the game tracks rotation beyond 360 degrees or 2pi and is actually trying to unwind the craft through all the rotations that have occurred?

http://youtu.be/eYFKu1xVdxk

Test 3: This is very similar to Test 2 except I intentionally transfer fuel to a burned out booster to introduce spin. Again the SAS does correct the rotation initially, but continues full force over correction after the spin is damped. Toward the end I use RCS to stabilize the craft with SAS still enabled. Again I'm wondering if it's trying to unwind all the rotations that have occurred instead of moding the crafts HPR angle by 360 or 2pi.

http://youtu.be/A-Nrt8zka0A

The spin is introduced at 2:50.

Edited July 25, 2013 by Sardonyx

[wudupdogz]

With regard to test 3, tap "f" after desired attitude is attained.

[TheHengeProphet]

Tapping any control direction is roughly equivalent to tapping F now, as it deactivates SAS when under manual imput...

[Nodrak]

You are just noticing how drag affects things. Spin in space if you want to see how it works when momentum, torque, thrust, and drag arn't all fighting.

[FITorion]

Tapping any control direction is roughly equivalent to tapping F now, as it deactivates SAS when under manual imput...

not exactly. Yes but only for the axis of input. F disengages all axis.

[Tobyz28]

Here are my thoughts, I'll need to do more testing on my own but so far things appear normal to me...

For the rotation part: Your two engines are deflecting from their mount point outward in opposite directions causing the ship to spin. The SAS is not strong enough to correct.

For the spin portion: Similar to the first, there's too much mass/momentum for the SAS to correct from that large of a spin. The spin is also amplified by drag from the air given your still in atmosphere (30km is still significant)

I'll be testing if reaction wheel location has an effect on the type of spins or if it just acts on the COM (would love some Dev input to save me the time )

Edited July 25, 2013 by Tobyz28

[Sardonyx]

For the rotation part: Your two engines are deflecting from their mount point outward in opposite directions causing the ship to spin. The SAS is not strong enough to correct.

For the spin portion: Similar to the first, there's too much mass/momentum for the SAS to correct from that large of a spin. The spin is also amplified by drag from the air given your still in atmosphere (30km is still significant)

First let me say, I don't think the new SAS is bad nor do I dislike it. I'm just doing some testing here. The old SAS will hold this ship almost perfectly steady in launch. I disagree that the RCS/Reaction Wheels are not strong enough. If controlled manually there is plenty of force to cancel the rotation. The new SAS undershoots the force necessary though. I think there's a happy medium where it can hold the ship in place by applying a little more force, but not just going between 0 and 100. It really is probably tuning a constant on the feedback controller. That said, all in all it's not bad and certainly better than the old one blowing through a ton of RCS fuel whilst shaking a ship to pieces

[Sardonyx]

Added another test:

Test 4 - This is a small craft with 2 Reaction Wheels. One at the top near the capsule, one at the bottom near the engine. There's some slight roll at the gravity turn, but overall it's relatively stable.

[Nodrak]

Been flying some larger ships now (to get more inertia), and there seems to some sort of bug.

1) Take a ship in a stable orbit facing a certain direction. (0 heading for example)

2) With SAS on, apply full force and turn towards another direction (90 heading for example)

3) Stop applying force halfway there (45 heading)

4) Wait until SAS gets a heading

My final heading in my new station was ~270. You can tell this was where the SAS wanted to be, because of how it was managing the control forces.

This issue may extend to the 'off center' mass balancing which could explain some of the 'my ships wont stop rotating' issue. As the SAS unit will generate continuous force by setting its target in the wrong direction.

Edited July 25, 2013 by Nodrak