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obrien979

MechjJeb Rendezvous Issues

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So I updated to the new MechJeb (2.7.0) and I am seeing an issue with trying to conduct Rendezvous activities.  The initial burn towards target, once on orbit, starts off fine but then as the velocity meter starts to near the bottom and I get closer to the target the maneuver node on the navball goes nuts and just bouncing all over the place causing my craft to do the same. As a result I am have to use more RCS to try and stablize but the problem is reoccuring each time.  I have tried on several different ships and I am getting the same result.  

 

I am trying to use the mechjeb to have a manned capsule Rendezvous with my space station.

 

Any ideas on the cause and a fix?

 

Thank You

Edited by obrien979

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On 1/12/2018 at 1:50 PM, obrien979 said:

So I updated to the new MechJeb (2.7.0) and I am seeing an issue with trying to conduct Rendezvous activities.  The initial burn towards target, once on orbit, starts off fine but then as the velocity meter starts to near the bottom and I get closer to the target the maneuver node on the navball goes nuts and just bouncing all over the place causing my craft to do the same. {...}  I have tried on several different ships and I am getting the same result. 

No solution, same problem.  Perhaps also related, MechJeb seemingly always wants to do a victory cartwheel when he's gotten something out of the atmosphere, then has trouble reorienting for the circularization burn (if you wouldn't spend so much time torquing yourself 120deg off the flight path, you'd be in the right orientation for that next maneuver node, you mechanical numbnuts!)

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Turn off RCS when that happens. It will do the same but, once it reaches the Maneuver node, it finishes (usually around 0.2 m/s burn left). Granted, your vessel probably has to do a 180° turn. So you gotta need reaction wheels for that.

Mechjeb's RCS loves to go nuts when your maneuver node is near perfect. Because MechJeb has preferably "zero" tolerance.

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I've noticed that MJ is being more aggressive, but it's not usually a problem for me:

  • I design my ships to be undercontrolled--I typically don't use anything to turn in space other than the pod's reaction wheel and/or the engine-gimbal. It just means I have to plan ahead a bit more. I don't add reaction wheels to anything that has a crew pod until I hit 50-100 tons.
  • If your craft is well-balanced/symmetrical, turn the engine gimbal way down, turn off or turn down reaction wheels, and turn down or off the thrust on your RCS.
  • You can also set the maneuver node tolerance in MJ to 0.2m/s, instead of 0.1m/s. That's usually fine and close enough. I do that for larger craft that get a bit floppy.
  • If your craft is a bit floppy, it helps to have the controlling part near the center of mass. Otherwise you can start some bad oscillations trying to correct a control vector that different from what the center of mass is pointed at..

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Is this specifically using the rendezvous autopilot?   I tend to use Maneuver Planner to do the three steps individually (Hohmann transfer, fine tune approach, and then match velocities) and haven't noticed behavior like that.

Edited by MaxwellsDemon

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On 1/25/2018 at 3:27 AM, FleshJeb said:

You can also set the maneuver node tolerance in MJ to 0.2m/s, instead of 0.1m/s. That's usually fine and close enough. I do that for larger craft that get a bit floppy.

This is helping quite a bit. I'll play with the other suggestions as well.

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