Dynamic Input works fine when placing valve, but not when placing a support. The Dynamic Input is from the base point (0,0,0), not from the nearest fitting or pipe intersection. Support has to manually be moved to location desired. If moving the support after insertion, the Dynamic Input is from the insertion point of the support. Is this a bug or a settings? I can't find anything that addresses this problem.
There is a way to place a support dynamically from a particular basepoint. I just have to write it down. You start with placing the support, then telling it the base point is from another point. If its not already on the forums, I'll post it up.
Okay, so the problem is with AP3D, confirming what I thought. I'll discuss the situation at a conference next month. I have three work-arounds. The first is to draw a simple ACAD line from one of the pipe nodes and offset it to where you want the support to be, and then erase the ACAD lines after the support is placed. The other isn't much better. Do an ID at a base point (i.e.structural grid) and write the value down. That will be based on 0,0,0. A quick calc will give you the exact X or Y for the support (the pipe will determine the other coordinates). Then use the Dynamic Input. The last is to do a Distance from the support node to where you want the support to be, and then move it X or Y in that direction. They're clunky, but they work for now until support placement method is fixed. I'm sure there are other ways.
Once a support is placed, say on a rack grid, it can be copied or arrayed like any other ACAD component. The user needs to keep in mind that, unlike valves or fittings, the type of support can't be substituted after placement.
A colleague sent me this a while back, placing supports in a known position from another fitting:
Let me know if this works for you.