How to change the length of the object with configurable joint attached

I am trying to reproduce the tetrahedral robot with physics simulation

Here is the video for the robot http://www.youtube.com/watch?v=dhL4JrvIFn8

I am not sure if it’s the best way but I tried to connect all the rods and nodes with configurable joints whose XYZ motion are locked and break force and break torque are infinity.

Then I tried to change the length of the rods. The joints are not working as excepted. Some joints are connected at the previous point and some are broken. From the step mode it can be seen the anchor point is moving as the rods scaled.

Is there any method to get the joints working properly? Or is there any other better method to reproduce the robot? Thank you.