Algodoo

Because it needs to be on the block, I think...

first of all, scene.my.motor=scene.my.motor=true makse no sense. If you do sth. only do scene.my.motor=true. There's no need to selfassign a variable. Second of all, you need to open the console(f10) and initialize the variable so that it wont break. so write ni the console scene.my.motor = false;
then you can type {scene.my.motor} in the motor field of your hinge. If the variable is not assigned in the console, what is algodoo supposed to give the hinge? That's why the code breaks at that instance.