I made two pages for the google-code wiki and if you want me to add them to this new one I will.

I have made a hopper that shakes, the two pistons are set to oscillate, it would also be possible to shake it along another axis but it doesn't seem to need it

hopper1fix.skp

The problem here is the Out Skin, it is one object set as default and such nothing can pass through the hole, the solution to this is to make it out of multiple objects. Four would be the best option as you would have one object on each side of the hole. You can see this if you remove the outer skin, you may also wish to change the accel of the servo, 10 seems to work.

To make the car go backwards you need to create a second motor that accelerates in the reverse direct, either by creating it along the same axis but dragging it in a different direction (Eg you created the first one dragging the motor towards the car, this time drag it away.) Or creating another motor joint dragging it in the same direction as the first joint you made and setting the acceleration to a negative value. For turning, you need to create some extra blocks on the car, attach the motors to these new blocks and then create servos and group them with the car and attach the servos to the blocks.

Once the simulation is playing, right click on the car and choose camera follow

if you are sure that the controller is working (I'm assuming you've used it for games) you need to name the controller that you want to control depending on what you want to use to control it, the correct syntax is joyLX this would make the X axis of the left analogue stick control that joint.

I think Sketchyphysics might have problems with arraying thing, i know it has problems with scaling but i'm unsure about array, try copy and pasting them and see if you still get the error.

Just save it without pressing the stop/rewind button

To get this i modified the 1.1 to have the joints grouped, each Ball Joint is grouped with the door nearest to it meaning it can move with the door around the Hinge/Servo (Joints will require reconnecting if you group something). The ball joints were already attached to the connecting rod.
The disconnecting at high angles, the door on the hinge it levered away from the hinge as it is being pushed against the central static block.
The disconnecting of the servo door is due to the fact the the distance between the two doors is 46' 8 16/16" before the play button is pressed, when both are rotated 90 degrees clockwise about their joints the distance between the same two points is 47' 11/16". To solve this problem a two part 'chain like' connecting rod is required to prevent disconnecting.

I've managed this so far.

Need Help 01.1X.skp