Occasionally, I'm not quite sure when, you can't put braces on top of other braces. However, at other times you can.

I cant find friends.

I've got like 5 different versions of about 5 different vehicles because i can't delete them once i've saved them :) i dont mind its just harder to find my finished product, thanks

In level 11(the second head-on collision), you will automatically succeed because the structure dummy you are supposed to collide with immediately collapses; so the game thinks you collided with it.  

pistons - help give a sudden push off the ground (jumping)

Rope- Basically braces but a Little more free moving 

wheels- not the actual wheels you use to move but ones with links on them

detachable links- press a chosen hot key and press it and it destroys the link thus separating that from the car.

More rockets- Have a high power rocket and medium and low power.

balloons- hot keys to pop them but they help pull you up (ropes my come in handy)

Fan / propeller- For floating contraptions, help propel it in the desired direction (not as fast as rockets and hot keys for each fan)

                                     ~Thanks for reading