hello im making a few vehicles for a map and ive read some tutorials on exporting and adding nulls but they only work for weapons i guess so idk when i put all my mshs under one null i named dummyroot and save export and stuff they never work in MshEx

That's because, as explained in it's readme, MeshEx beta 3 only works for static objects, such as props. To convert other models, you'd need a professional exporter, or ask someone else, who does have a professional program, to convert your models.

MshEx also works for unanimated vehicles (such as hovertanks, landspeeders, and some flyers).

Nulls do work with vehicles. Props too. Pretty much anything.

well its not a vehicle jus tskins for one i dont have animation fo rit just the mesh and texture so basically its jsut a prop and it does it with my props,people,everything

I meant vehicle meshes.
Now, could you give us a little more detail about your problem? The impression I'm getting is that you try to put in nulls (dummyroot, hp's, etc.) and they don't work with MshEx, so MshEx crashes. Is this right? How did you go about setting up your nulls?

On a side note, you cannot export people with MshEx.

well i just made one null and named it "dummyroot" and dragged all the meshes under it but when i dragged them they didnt go in they just made like copys of themselves and when mshex crashes it gets half way through its process and crashes. but ends up only giving the exported msh a few lines in the notebook

How many polys do your moels have? Are you trying to export anythign animated? What settings do you check when you use Crosswalk to export the scene to a .xsi file?

ummm idk how many polys it has but i click "EXPORT SELECTION ONLY" "CONVERT GEOMETRY TO TRIRANGLES" "EXPORT XSI NORMALS" and i dont try exporting animation it doesnt have any

And do you uncheck what has to be unchecked?

yeh theres only one thing to uncheck right?
and idk wat it means "place all meshes under one null" and only under one cluster

You have your dummyroot null.
You select everythign you want to export, then click-and-drag it over the dummyroot in the explorer and let go. You have just placed it all under one null.
Select the dumyroot. Hit ctrl+t. Export with Crosswalk, then MshEx.

Make sure you have the proper Crosswalk version (it used to be 2.6, its something else now). And when it says drag the mesh under the dummyroot, it means in XSI explorer, drag the mesh names over the name 'dummyroot' and drop them there. If you understand what you're doing, then you would know that you are placing them under the dummyroot in the hierarchy.