The solution: Instead of one arch, I built the arch out of a number of groups, (like bricks in a real building) and grouped each sub-group together to make one arch shape. GROUPING GROUPS: Even more advanced shape physics. (No support for a CONCAVE hull as of yet.) And it behaved more like a half circle than an arch. You can see that SP 'drew' in some lines to make this a 'CONVEX HULL'. WTF?!! After using the DEBUG command, I saw this is what was happening: The arch wobbled back and forth as you would expect, but when I dropped a ball on it from above, the ball did not fall into the arch.

I encountered this situation when using 'CONVEX HULL' to make an upside-down arch: So how do you fix it? Let's look at a similar shape that I had a problem with. You can see that the convex hull made a shape similar to the gear above, but if you tried to make it 'work' with another gear, it wouldn't. (Like a boat.) This has some limitations, as I'll describe next. It takes a shape from end point to end point and makes a closed 'hull'. And it is exactly what the name describes. It does not move, however the ball will fall and roll down its slope. Therefore this option is mostly used when making a 'ground plane' for everything else to 'ride' on. This is beneficial when making a 'hill' for something to roll down, or a multi-pitched slope. This draws a mesh around your shape to create the outlines. (You can see the original wireframe as the cylinder falls below.)ĪDVANCED SHAPE PHYSICS: There are a few more shapes that are provided for you when the normal ones don't work out. SP will squash a sphere to fit the cylinder shape relatively well. 'SPHERE' actually works quite well for a short cylinder. So what can you do if the shape gets set wrong? Try another shape. For example, if I turned this cylinder on its side, it would 'roll' end over end like a quarter being flipped. If any other object interacts with this cylinder, it will hit the black wireframe, NOT the actual grouped shape! You can purposely set objects to the wrong shape for fun. This cylinder object was set to 'cylinder', but by using the DEBUG option, you can see the black wireframe shows SP thinks it is actually on it's side. (See below.) AN INCORRECTLY SHAPED OBJECT: Also, just because you make a cylinder and set the shape to cylinder, doesn't mean it will be oriented correctly. SP will make a black wire diagram of the object AS IT SEES IT. After grouping an object and setting its SP shape, select this option and press RUN. Just because you grouped a Cube doesn't mean SP 'sees' it as a Cube! USE THE SHAPE OPTION ON EVERY OBJECT YOU CREATE FOR SP!!!! DEBUG: Use this option to check the shape SP 'sees'.

SHAPE: Sets the shape that SP sees the group as. Shape Physics The other two right-menu options are SHAPE and DEBUG, and they are used together. IGNORE: The object will not move, and other objects will not interact with it. STATIC: The object will NEVER move, no matter what happens to it. The STATE options are: FROZEN: Image will stay in place (it won't fall) until it is hit by another object, then regular Physics takes over. They are accessed by Right-Clicking a grouped object. Setting the STATE of the Object After making a grouped object, there are 2 main attributes to use when creating an object to use in SP. These shapes are already grouped and ready to use, all you have to do is draw them where you want to in your model. There are also auto-shapes provided through a toolbar that is installed with SketchyPhysics. Physics will then be applied when you press the RUN button. If you start by making a cube and grouping all the parts into one object, the object will be recognized by SP. The first thing to note is that SketchyPhysics ONLY WORKS WITH GROUPED OBJECTS.

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