Trying to create a dynamic block to stretch a conveyor

[coffman.davidjr]

Hello,

This is my first post to the forums here, and I'm hoping to get some assistance with creating a dynamic block. I can create a dynamic block to stretch a simple shape just fine, i.e. a rectangle. But I'm trying now to add 2 strech functions to a conveyor model. As you can see from the drawing, this is a complex shape that is giving me a hard time. The "length stretch" is supposed to only lengthen the segments highlighted in yellow. Same goes for "Side wall stretch" 

Seems that when i do the sidewall stretch, it works, but still doesn't work all the way. Some of the vertical lines do not stay connected during the stretch.

The length stretch is an absolute disaster for me. I've tried multiple times, and this latest result is the best looking. It doesn't work at all like I want it to, but it doesn't leave some points in place, and then stretch the rest into something resembling spaghetti. 

Any idea what I'm doing wrong here? 

I'm using AutoCAD 2015 if that helps

[Libbya]

There are a few things to understand about stretch actions.  The shape/position of the stretch window is important.  Any vertex/point within the window of a stretch action will be moved the distance the parameter grip is moved X the distance multiplier of the action.  If an object is completely within the stretch window or completely outside the stretch window then the entire object is moved. 

In your block, the 'side wall stretch' is easily accomplished using a single stretch action, provided the stretch window is sized correctly and the correct objects are in the action's selection set.

The 'length stretch' may be a little more complicated and in order to help with that, I would need more info on exactly how you want the length stretched.  Please draw a 'stretched' version of the conveyor so that I can see exactly what the finished product of the stretch action would be.  Are there always 6 equally sized 'humps'?  Or are 'humps' added when the block is stretched?

The attached file has the 'side wall stretch' corrected.

[Libbya]

In other words, is the desired 'Length Stretch' like what is in the attached file?  Examine the 6 stretch actions, see where the windows are, look at what objects are in the selection sets and look at the distance multiplier of each.  Let me know if you have further questions.  

[coffman.davidjr]

Thank you! Looking at the multiple stretch actions, I see where I went wrong. I was attempting to do this with a single stretch action. I wasn't aware that I could utilize one action grip to control multiple actions.

But my question now compounds itself. The lower tabs (highlighted in green) can have no more than a 30" spacing on centers. So Is there a way to add/remove objects as the stretch action is being performed?

Thank you again!

[Libbya]

Yes, if I understand you, that can be done through the use of lookup tables and visibility states but that gets quite a bit more complicated and would not allow for stretching indefinitely.  Before delving into that, I'd like a little more description of exactly how you want the stretch action to work.  I assume from your original block and your description that the 'humps' are always all the same size so that they all stretch the same amount until they reach 30" O.C. at which time another hump is added and they all shrink accordingly so that they are all the same size.  Is there a maximum length to the conveyor?

If that is correct, then the way to accomplish that stretch action would be to have a visibility state for the 6 humps, another state for 8 humps, another for 10, another for 12, etc...  Then the appropriate stretch actions would need to be added to each state.  8 humps would require 8 stretch actions, each with correct window, selection set and distance parameter.  10 humps would require 10, etc...  Then a double lookup parameter with an input of the x distance would be needed that would automatically switch the visibility state when the length was stretched to the point that another hump should be added.

Unfortunately, it seems like 2015 has an issue with the double lookups where it requires that you click the grip a second time after the range has change in order to update the visibility state.  Grrr....it worked fine in 2013...

[Libbya]

It looks like the double lookup only has an issue with the XY parameter.  I liked the simplicity of the single grip. but it actually works to trigger the vis state change with a linear distance parameter instead.  See attached.  When the total length of the conveyor exceeds 236, the visibility state changes automatically to show 8 humps instead of 6.  You can add visibility states as necessary and then add the appropriate range to the double lookup in order to trigger the visibility state changes at the appropriate lengths.