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Need help, my construct rolls when I try to yaw.


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I have a medium hauler (500 - 1000 tons, S construct) running the DU-Orbital-Hud script from Dimencia and Archeogeo. When I am hovering, with brakes on, and I want to orient my ship with a yaw, I get a lot of roll. I have tried several things to eliminate the unwanted roll.

 

* The construct is symmetric about the x axis.

* Moved all hovers and vertical boosters to the outside edge of the grid for more stability. This seems to do nothing, so I suspect they always provide thrust through the center of gravity.

* Placed adjustors so that they should not produce mixed modes of rotation.

* As best as I can tell, my CM (center-of-mass) is at x, y, z = 0, -18.5, 42 (there should really be a readout of this value somewhere)

    * Adjustors are placed back-to-back where possible, usually with a gap, so they are symmetric about the CM.

    * Pitch adjustors are aligned in the z direction, in the YZ  (x = 0) plane through the CM.

    * Roll adjusters are aligned in the z direction located in the  XZ (y = -18.5) plane through the CM.

    * Yaw adjusters are aligned in the x direction,  located in the XY (z = 42) plane through the CM.

    * The yaw, roll and pitch torques are 3.52, 3.47, 3.5 MN.m

 

The yaw adjusters seem to work fine (no roll) when I am flying, I assume that has to do with the stabilizers in the back.

When I yaw, the roll adjusters are also firing, which makes no sense to me.

 

Originally I also pitched during the yaw, but after much playing with adjustors that went away, and the pitch adjusters no longer fire during the yaw.

 

This may be unrelated, but there seems to be some control bugs, W is pitch down, and S is pitch up, A/D is yaw left/right, and Q/E is roll left/right. This is different then how it is set in my Controls section.

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After I made the post above, I decided to make a simple test construct from an old hauler I was taking apart. I kept only the seat, landing gear, and adjustors. the seat was already using an older version of DU-Orbital-Hud. With no extraneous elements, I was able to position the adjustors perfectly, and they performed perfectly. Only the yaw adjustors fired with the yaw command, and only the roll adjustors fired with the roll command. This is what I need to achieve on my medium hauler.

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Distribution of mass across the construct is important. In Build Helper look at the Inertia Matrix. To control yaw there must be equal mass above and below the horizontal plane. Preferably, you would want all mass to be on the horizontal plane but that isn't really feasible. Keep the Inertia Matrix open as you place mass on your construct and watch the number in the middle of the right column. Controlling mass for pitch and roll is relatively easy but controlling for yaw is the tricky part.

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7 hours ago, Underhook said:

You are probably aware but I'll mention anyway that the centre mass lines are visible in build mode

I can see the lines. I had trouble with the parallax effect at first, making it difficult to determine exactly where those lines crossed elements in the construct. Eventually I released I could use the inclination gauge that turns on with the suit lights. I then make sure my inclination is set to zero as I line up elements with the CM. 

 

 

Thanks for the video link. I was hoping someone would know of one.

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I have finished rearranging the elements in my ship, and it yaws flawlessly.

 

The problem I was having was with the YZ/ZY elements of the matrix. After looking at the posted video, I looked up the formula for the inertial matrix. The formula is the sum over all the elements of the quantity m*Y*Z, where Z and Y are measured from the CM. I needed that sum to be zero. I decided to set z = -44 as my CM and proceeded to arrange every possible element at that height. Of coarse the hovers and boosters were below CM and the stabilizers were above CM. They partially balanced out, but the CM was still below z = -44. I then placed the air brakes above CM and tweaked the wings up and down until balance was achieved. 

 

Thanks for all the help.

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