Why does MechJeb....?

[tg626]

Keep shutting off RCS thrust?

I have a "shuttle-esque" asymmetrical lifter and as it nears burn out it needs thrust from the RCS (vernors) to stay true. I *think* it would be fine if MechJeb didn't keep shutting off the RCS thrust only to reactivate it at full force to try and recover from the inevitable spin.

If I manually goose the attitude controls on the way up it seems to help, but I don't understand why MJ seems to "reset" application of corrective RCS thrust on a semi-regular basis.

Edited April 5, 2015 by tg626

[Guest]

It isn't possible to code an autopilot to handle every specific situation that every user throws at it. You are most likely experiencing a specific situation that for one reason or another, mechjeb wasn't designed to handle. Mechjeb is like a screwdriver set with multiple driver bits. The autopilot is trying to figure out which bit to use on a screw it hasn't seen before. You are going to have to figure out which bit works best for special case situations. That is just a quick and dirty answer based on the info you have given. You are going to have to supply much more info to properly diagnose the situation.

[sarbian]

What Otis said.

[tg626]

Well I was going to make a video showing the behavior but I couldn't resist tinkering before I did and if course it flew fine.

It boils down to how mj behaves with a craft that lacks pitch authority. It does the same thing with planes as well. But I guess in the end what it is really showing is a design flaw. In the craft that is. I still wonder tho what in the logic makes it give up and start over when it can't attain the desired pitch/ flight path.

[moogoob]

That's odd - MJ's always allowed me to toggle RCS manually. Ascent, landings, whatever. What autopilot module are you trying to use? Maybe there's an advanced option somewhere you clicked? (for example, one optional thing MJ does is use any rearward-facing RCS nozzles as engines if you either have no engines or have run out of fuel)

[Guest]

Well, it might be easier to upload the craft file, post the link, and provide a few steps on how to reproduce the error. A short explanation of the intended goal, like reach orbit or orbit the mun or whatever, so that we can try to reproduce. Recording video, editing, and uploading is time consuming, I know. Uploading a craft file takes about 1 second.

[sarbian]

I would like to point to a recent post in the MJ thread that show exactly how I like bug to be reported >>>here<<<

I was able to find the origin of the bug ans fix it in less than 15 minutes. The bug was far from new but I never had a clean explanation and it made it hard to track down. With a save and simple steps to duplicate it was easy.