[Help!!]Cylinder alignment problem


I have a new project about crane simulation. Firstly,I set all the parts to be rigid bodies and set necessary rigid body joints.

Now here is the problem, i used rigid body joints to match cylinder rod, one side of cylinder rod with a joint and another side tracks to cylinder tube . There are always alignments either on the joint or on the tube. I know that I could use track to constraints but it seems not working well in the game logic.

So, does anyone have any idea other than using rigid body joints???Should i use Python?? What is your suggestion or anything comes to your mind :smiley: all welcome!

Thanks in advance!



crane.blend (494 KB)

any idea??

The problem is that you have the object tracking something. If you want it to move with it you have to make it a parent. What you do is click the object you want to be parented (green arm thingy) and hold shift and right click object you want to parent it to (gray cylinder thing). Hit CtrlP and make parent. That should fix problem
If not then tell me

Hi, thanks but what i want to do is just to stick all parts to joints so that i can move them freely.Therefore, i dont think parent will help coz i wont be able to move any child object freely without moving the parent.


I wouldn’t do that with physics. It makes is hard to setup, very inefficient and will mostlikely result in very strange results.

The cleanest solutions would be to animate the crane with IPO’s or with Armature actions. Because the crane is not bending (it is not organic) I suggest IPO’s (called F-Curve in 2.5x). The animations will be clean and always fit.

You can control the animation when the actuators are in property mode.

I know :frowning: But it is my project and i was asked to do it in game engine using Physics. =(

The question is: what needs to be physics?

You can use animation for the crane and physics for the rope (only the free hanging part of it) and hook.
That is difficult enough and this is where the physics is important.

hmmm…never thought about this before…interesting!! Can you explain more in detail?? Thanks!!

You should ask what exactly should be physics and what can be made differently.
A complete cran with all details in physics is simply impossible. So you need a simplyfied model anyway.

You should use physics only where it matters. As I do not know what exactly you need to do I can only guess.

A simple crane would be:

  • a point in the air where the rope/chain is fixed at.
  • a hook or whatever at the rope/chain.

For ropes/chains you can use rigid body joints. Do a little search in this forum you will find a few thready with this topic.
You can mount the hook/shovel at the end of the rope with rigid body joints too.

I haven’t done anything with such things. I just assembled a small chain just to see that it works. So I can’t really help with that.

The whole point is you need the rope and hook regardless how the rest of the crane is build.
So you can concentrate on this first. It does not matter if the crane is static, physics or if it exist at all. You can assemble the start of the rope at a cube in mid-air first ;).

As I said. It depends what you are supposed to build.