Need help on TRACK TO constraint


I am total new to Blender,already saw dozens of tutorials, got a lot of those. But still need help on some issues.My project is about real-time simulation of crane in the Blender, for a beginner, i started from make 1DOF boom with one cylinder.

I choose all the parts as rigid bodies and make constraint with rigid body joints so that cylinders and booms are connected with each other.Also, i have the ‘TRACK TO’ constraint to rod and body of cylinder. What i want to get in the simulation is like when the second boom falls, the cylinder rod retracts and stops when it collides with the cylinder body.

Here is the problem, when i simulate in the game engine, the TRACK TO constraint does work and the second boom just falls and the cylinder rod just falls.

I have been doing this for the whole day but can not find any solution. Could someone offer some ideas or anything that i made is not correct ? Thanks!!!

P.S I have uploaded the file.See below =)



track_to_constrain.blend (385 KB)

Hi and welcome to Blender!
Try turning on physics visualization. (Game -> Show Physics Visualization). This will help you to see if things are setup properly. For example an objects center might be offset from its geometry, and/or rotated incorrectly.
If this does not help could you post a blend file of what you have so far? That will make it easier for others to diagnose the problem and to provided you with good solution.



Thanks for your tips. Acutally, i have already linked the images but dont know why it doesnt work =) I edited again. Thanks!!


ignore this, was fixed

I got it working please wait while I try to come up with an explanation…

Here is the working file:track_to_constrain.blend (64.3 KB)

First off “Track To” constraints do not work in the game engine. So those did nothing.

2nd: all of the objects where off center with their geometry. If you enable Physics Visualization you would see that their physical bounds (shown in white) are only half in their visual geometry. To fix this you have to select all the objects and then at the bottom of the 3d view: Object -> Transform -> Origin To Geometry.

3rd: In order for the constraints to be where you see them the object has to have its scale applied (possibly a bug). Select object, press ctrl+a, and select “Scale.”

4th: A “Generic 6 DoF” rigid body joint constraint can be used as a Track To constraint. But setting a Child Object to the constraint makes the constraint not work (possibly another bug.) You might want to refer to the wiki to learn how to use a Generic 6 DoF rigid body joint constraint.

I hope this woks for you. Have fun.

EDIT: I knew I forgot something. When using a Generic 6 DoF constraint the objects that affect each-other do not seem to collide with one another. I got around this by setting the limits under the Z option of the constraint. Now they seem to collide with each-other but it is really the constraint doing the effect.

Hi,really thanks for your help!!! I am still digesting tips. =) Thank you!! Thank you!!!

To skykooler
xD anyway Thanks for pointing out!