Collision Box

Wow, I’ve started 3 or 4 threads this week. Ah well, I’m really workin and bumpin into alot of problems. I’m not going to post a blend because it’s exactly the way it sounds.

I have a collision box problem: I have a Ghost Cube with a Collision Sensor. So far so good. I put a cube in front of it. No problem. I put something behind it (Or anywhere else near it) and Parent it, and then the Collision box just falls down. Is there a way around this?

I’m confused. You have a cube with Ghost applied, correct? And it falls if you parent something to it?

the col box is parented to aregular box with no phisics.

Various strange things can happen when dynamic objects are parented…need to see the .blend to find out exactly what.

well is it ok if its over? smile. Check the axis of both, and make sure the center is in the center of both of them.

Are the masses of each object similar in size? Are the bounds of each touching? May causing it to bump over? Please show a picture of you logic blocks with the boxes showing in 3d in the top?

What is the collision prop set to? Are the boxes both dynamic?

Aarrgg. Okay. Here is an example file. Hope it helps

I am really confused by the file. I see one box going up out of sight and the other just lands on the plane?

the collision sensor doesnt do anything…

I played with it…and discovered something, a weird thing…

So, when I unparented them, the child fell down to where it was originally made. So I moved it back up and pulled it farther away to see it better.

Then did a ctrl a. Then parented it back again. Then I clicked show physics visulization in the game menu.

Then I deleted the bounds for the child, and pushed compound for the parent, so it knows it has a child.

Then p. Now there are 3 boxes, two do what they are supposed to, I think, I didnt try the keys, and the 3rd one, is where the child was before pressing play.

I dont get it and am going to bed, lol. But you can download the file and dont change the view, just p and watch it. Might help.

Anyone passing through is the above normal for parented objects? In the picture below, on the left at the top is the parent, and on the right at the top is the parent and child, and at the bottom is a ghost child.

Later: after playing with the file some more (always learning), I unchecked use visuals, and changed the mode to solid, and now the parent, and the ghost are all that show. The one inside the parents box doesnt show.

So is it still there? LOLOLOLOL. that was fun!


You didn’t clear the child’s parent inverse, which means its collision box appears in the wrong place. About the main problem: I think it’s a bug in the collision sensor. I’d try to use ray instead.

Thanks very much! See how much I learned, now I hope I dont forget it.

But how does parent inverse get set? I’ll look in the wiki.

It occurs if parent is moved or rotated before parenting. Parenting uses parent’s local coordinates and doesn’t take into account if the parent had been moved or rotated since it was created.

After you clear parent inverse, the child gets misplaced. You can fix it quite easily: first move cursor to selection (shift-s, cursor -> selection). Clear parent inverse (alt-p), return the child back to its initial position (shift-s, selection -> cursor) and finally rotate if needed.

This was happening to me just yesterday!!!

Thanks again, thats exactly what I did, lol.

If you do the ctrl before parenting, does that inverse thing still get set?

You mean Ctrl-A? It applies rotation, but not location; it only helps if parent is rotated, but not if parent is moved. In case the parent has been moved from its original location – unless there’s “Apply location” -key hidden somewhere – you have to do it the hard way.