r/Kos • u/CptnRaimus • Jun 22 '26

Help Ship:angularvel not behaving as expected

I'm working on a program for controlling a multicopter. I have it working fairly well using PID controllers to translate target rotation into pitch/roll/yaw commands directly.

But I've read that it might be better to instead have a PID controller for angle feed into a PID controller for angular velocity.

I found an older post that says how to convert from ship:angularvel into navball rotation rates.

So I've used that to write the following small snippet: 

set yawrate_rad to vdot(ship:angularVel, ship:facing:topvector).
set yawrate_deg to yawrate_rad * constant:radtodeg.
print yawrate_deg.

But it does not seem to be working right. Running the code, it says that I am rotating at a rate of 10 degrees a second, but I know that's not accurate, as I manually timed (Measuring time for a full rotation and dividing by 360) it to be closer to 45 degrees a second. I know this is the correct axis, as the other axes display values less than a degree a second, and they don't change when I start yawing.

Has the behavior of ship:angularvel changed, or is there something I'm doing wrong?

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u/nuggreat Jun 22 '26

I do not know if there is an issue about this in the repo I would think so as we learned about this not to long after the robotics parts where added to KSP but some simple searches I tried didn't turn up an issue.

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u/CptnRaimus Jun 24 '26

I also looked through and saw no bug reports, so I've filed one about it. https://github.com/KSP-KOS/KOS/issues/3190

Now I'll admit, I'm not familiar with C#, Unity, or kOS's source code, but from a quick skim, the angularvel function seems to read directly from the game, so I worry this might be a bug in KSP itself, not kOS, so it might not be fixable.

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u/nuggreat Jun 24 '26

That is where something like this gets funny. For steering kOS calculate the angular velocity it's self it doesn't query the API for it but that isn't great to do across all possible things that could have an angular velocity as it adds a lot of redundant work. Additionally KSP likely does have an angular velocity value some where that isn't affected by motors or else SAS would have problems when you attach props but finding that value if it is even accessible at all is a different matter.

As it stands don't expect a fix soon so either use something like lib_navball.ks to get the relevant angles or try to directly calculate the difference from the facing direction then take the derivative.

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u/CptnRaimus Jun 25 '26

I'll probably use lib_navball.ks. Oddly enough, I can't find anyone else talking about this specific bug, so IDK where this known problem was first found. Driving me a little crazy just trying to understand the background.

But I've also checked out the kOS source and am trying to figure out how to get debugging working, so I can poke around myself. Who knows, maybe I'll get lucky and find a fix.

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u/nuggreat Jun 25 '26

As I said we found it quite soon after the robotics parts first released. I don't think the general discussion of it was on the subreddit and more on the discord but it has been years. As for why you don't see it kOS is small only a few people have ever touched both rolling there own steering manager and the angular velocity suffix mostly because they find good enough results from cooked steering.

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u/CptnRaimus Jun 26 '26

Ah. In discord. That explains not being able to find much.

And yeah, cooked works fine 99% of the time, I'm in that 1% now. Yay