http://www.istockphoto.com/vector/wagon-wheel-10737578 http://www.istockphoto.com/vector/horse-drawn-carriage-wheels-16511232 http://www.istockphoto.com/vector/ancient-horse-drawn-carriage-wheels-16514747 http://www.istockphoto.com/vector/wild-west-chuck-wagon-wheel-13461460

1. http://www.istockphoto.com/vector/wood-plank-background-41780510
2. http://www.istockphoto.com/vector/wood-grain-light-horizontal-and-vertical-seamless-pattern-5486308
3. http://www.istockphoto.com/vector/old-west-hanging-sign-6646765
4. http://www.istockphoto.com/vector/fence-peices-d-i-y-fencing-1237521
5. http://www.istockphoto.com/vector/wood-structure-5012603

In the attached screenshot, the stress on p2 should pull p1 of the free end of the engine toward p2, so that the engine begins to swing. as it is now, p2 on an engine is nearly as firm as an immovable point.

since p2 can only be pulled off the rail by items that update after the engine, it should calculate it's distance from it's ideal line, and then adjust p0 and p1 before it updates p2 to it's new place.

this would be a good thing to add to [updatePoints] in the engine, for the p2 to pull p0 and p1 toward itself as a force at the same time as gravity.

Wheels are modeled super similar to balloons. I should allow them to collide with each other and with balloons as well.

possibly have both balloons + wheels extends from a MMCollideCircle or something, so that they can share code.

Update to use Jacobi Method and average the changes of all constraints for a smoother motion. This should reduce reliance on the order that items are updated

https://zalo.github.io/blog/constraints/

if a part gets accidentally attache somewhere, it's stuck.

allow detaching all objects at a point, or selecting an object and detaching only it from everything that its' touching.

I think it'd be fun to make the logo out of the available parts. then when the user presses "play!" or "start!" or whatever, the logo animates and falls apart then the tutorial fades in or something.

A normalized vector pointed at the point will give the x and y step for that point on the wheel

Sum the vectors for all the constrain hits of the wheel. Those vectors point to all the collisions that frame. Then point perpendicular to that vector, that's the direction of force from the wheel.

To power the wheel: for each of the four points: look at the difference in c and y during the next angle tick. Add that to its current location.