I want to make a test sign attached to a panel arm called "video_arm.mdl". I tried several methods but non of them worked:

I opened the test sign instance (info_sign_sp_clean), grouped all brushes in it and made them a func_brush. Then I placed a third logic_relay in it with the output[on trigger-"name of the brush"-SetParentAttachmentMaintainOffset-parameter "monitor_attach"]. I parented it to something I named "testsign_arm" and that's how I named the panel arm in my level. Result: the panel arm moved through the test sign -> failure!

Next I triedthis:
I opened the test sign instance (info_sign_sp_clean), grouped all brushes in it and made them a func_brush. I parented it to something I named "testsign_brush" and that's how I named a brush which I placed right between the test sign and the panel arm in my level. I made a logic_auto and set its output on [on mapspawn-testsign_brush-SetParentAttachmentMaintainOffset-parameter "monitor_attach"]. Result: the panel arm moved through the test sign, but this time the brush behind the sign didn't move either. -> failure!

I wondered why the brush didn't move so I made a simple map with only a button, the brush with the panel arm and the same panel arm, which I made a parent of a wheatley monitor. aaand...nothing - the monitor and the brush stood at one place while the panel arms went through them. I thought "there's something wrong with this video_arm.mdl!" so I wanted to parent the test sign to a func_movelinear, so that it moves the same speed and distance as it (and it would only look like the panel arm is pushing the sign). nope, the func_movelinear moved and the sign didn't.

last try:
I set anoutput to the sign [on trigger-"name of the brush"-SetParentAttachmentMaintainOffset-parameter "panel_attach"] and parented it to a normal 64*64 panel arm outside the map, which I wanted to move the same distance and speed as the video_arm.mdl, so that it'll only look like it's pushing the sign...another failure.

My questions:
1. HOW can I attach ANYTHING to a video_arm.mdl?
2. is there ANY way I can "tell" the instance info_sign_sp_clean to move?
3. WHAT have I been doing wrong in these 4 attempts?
4. Is collapsing the instance and then messing around with its parts a sollution?

You'll need to parent the vgui_screen entity (at the bottom of the sign) as well. (I'm not sure if it has a parent property, try adding it as "parentname" with SmartEdit off or send SetParent inputs if the property isn't visible. It needs a SetParentAttachmentMaintainOffset input too.) It renders the icons and other parts of the lit up sign. The attachment point for monitors is actually "monitor_attach", use the out-of-hammer model viewer to see attachment points (the second option below "hammer world editor"in the green authoring tools launcher.) In this case it's probably good to collapse, but you might want to instead save the instance as a new file then edit that instead.

Quickly reading this it seems that what your doing is parenting the arm to the monitor/brush. It should be the other way around. Name your arm (a prop_dynamic), then set the moniter/brush parent as the arm. Animate the arm. "Children" move with their "parents".

Also as you may have noticed the instance "info_sign_sp_clean" is actually a couple of different entities all-in-one. You'd want to parent everything that isn't "logic" to the arm. Logic (like logic_relay, logic_branch etc) have no distance requirements and providing they can identify their targets can work from anywhere in your map - but it is good practise to group them together/near the thing they opertate/control. You may have better luck collapsing the instance, or copying everything from it actually into your map.

Hope that helps

thanks a lot guys! I collapsed the instance and parented the vgui_screen to the panel arm and it worked. it turned out that my main mistake was that I wrote "monitorl_attach" instead of "monitor_attach".

PROBLEM SOLVED