topic Re: Constraint results do not match when adjusting part in AutoCAD Forum

Constraint results do not match when adjusting part

jurgenvdbrand — Wed, 18 Feb 2026 12:20:58 GMT

Hi everyone,

I'm working on a drawing of the following:

- A crane attached to a tower, along which it can move vertically.

- The crane has a boom with a cylinder attached on the bottom, where the cylinder adjusts the luffing angle of the boom

In the base drawing, I constraint the cylinder so it moves along with the boom when I change the luffing angle. The operator cabin stays in place, without having it constraint. However, when I copy it to another file, the operator cabin suddenly goes everywhere. I cannot really fully constrain it, since it still needs to be able to be adjusted up and down. I managed to constrain it, so that it only can move in the vertical direction, but when moving the boom, the operator cabin still shifts out of bounds (goes above or below the tower). Is there a setting that "fixes" the operator cabin and only rotates the boom and adjusts the cylinder, like it does in the base drawing?

Thanks in advance!

Re: Constraint results do not match when adjusting part

leeminardi — Wed, 18 Feb 2026 13:38:01 GMT

Please post a drawing of what you have so far.

Re: Constraint results do not match when adjusting part

jurgenvdbrand — Wed, 18 Feb 2026 13:55:58 GMT

I can't share official drawings, but this is the idea. In the base drawing, the tower (vertical rectangle) and the operator cabin (square) stay, while the boom can rotate and cylinder adjusts accordingly.

Re: Constraint results do not match when adjusting part

leeminardi — Wed, 18 Feb 2026 16:09:38 GMT

Please see the attached drawing.

I made blocks for the cabin, boom, outer cylinder, and inner cylinder (represented as rectangles but they could be cylinders).

On layer2 are lines with ends where pivoting should be done. The components are assembled using coincident constraints and,for the aligning of the inner and outer cylinders, collinear constraints are used. Change the luftangle to see different configurations.

[Edit] Double click the boom and the "luft" angle will be displayed. Edit the value. I know, "luft" should be "luff"! 😁]

You can move the cabin as you wish or could add constraints to only allow vertical moves.

Re: Constraint results do not match when adjusting part

catherine.watson — Wed, 04 Mar 2026 23:44:47 GMT

Hi @jurgenvdbrand, Did the previous suggestions help resolve the issue? If not, could you answer the following questions:

Are you using constraints on dynamic blocks for this?
What version of AutoCAD are you using?

Thanks, and I look forward to hearing from you!

Re: Constraint results do not match when adjusting part

catherine.watson — Wed, 11 Mar 2026 17:30:49 GMT

Hi @jurgenvdbrand, Checking in here, do you still need assistance with this issue? Below are some more resources on this issue:

For now, I will mark these resources as the accepted solution, however, if one of the previous suggestions resolved the issue, please go ahead and mark it as the accepted solution. Thanks:)