Modeling

As my project is mostly bound up in the electronics and electronics housing, the circuit boards and elements of which do not require modeling or structural analysis, I thought an animation as the demonstration of the principle would be most suitable.  I tried this a couple different ways.  The first was using SolidWorks animator, as I created my parts in Solidworks, and this was convenient.  The second was using Blender.

SolidWorks Animator is kind of best for exploded views and walkarounds of a fixed part.  You start trying to move things (at least things with coupled constraints), and it can be tough creating a realistic linear progression.  I thought I would try and demonstrate the principle of shifting weight to control a skateboard.  The way I see it, full speed ahead is neutral stance, the way I like to stand to be in full control at higher speeds (15-20mph).  Braking would be accomplished by actively leaning backward, assuming your front foot stays in the same place (which is best for stability).  The deceleration keeps you from falling over backward and is really quite brisk.  With its intended control scheme, the board does 20-0 in 4-5 seconds.  So this should be responsive enough, though we'll have to see how that plays out downhill.  It will probably take some adjustment and certainly be sensitive to user skill. 

Basically what I'm rebuilding is the entire electronics system, electronics housing and ebox, and possibly the battery, battery box, and the addition of a reinforced handle for easier carrying.  We'll have to see how many of these features get incorporated, but fundamentally, its the replacement of hand-operated RF control of the motor with the differential of front and rear arrays of force sensors. 

So in the new SolidWorks (2009), Animator becomes Motion Study.  I have a screenshot below to get an idea of the interface.  Basically it's just a timeline with keyframes and different layers for different parts, like Final Cut Pro.  



Motion is created automatically when downstream in the timeline you drag a part or parts.  What you're aiming for is continuous resolution.  The yellow lines are automatically solved motion, smoothed according to one of five interpolation modes i.e. linear, snap, smooth in, smooth out, smooth in and smooth out.   If they are discontinuous, you get a bunch of nasty stuff (refer to goofy.avi in the subdirectory).  This is not entirely intuitive, because in my experience, there's no overarching rule as to whether it will be able to properly interpret your motion as continuous.  Sometimes it does, sometimes it doesn't.  If you have parts with both large numbers of constraints and DOF (as I did in my animation), you want to make sure that when you move things, you try to do it as smoothly as possible, without a lot of wiggle of parts you don't really want to move.  These can contribute to discontinuity.  Also, although I'm not entirely sure on this, it helps to press calculate motion after each time you do a change, instead of waiting to the end.  This lets you pick out discontinuities as they happen, and you can just ctrl-z and it goes back fine.  So build up a movement at a given keyframe iteratively, moving one part a bit, then calculate, another, calculate, etc.   If all you have is a start and end, this is fine, you don't have to do intermediate keyframes, it will interpolate even complicated movements, with the above caveats.

In the end, I got a reasonably good render of the act of shifting weight, which I've attached in the subdirectory as better3.avi (delete the .html file in your browser address bar).  Note that the codec used to encode may not work on all media players (I've used it on WMP and VLC on Windows).

Blender seems to be a widely applicable and useful piece of software, and although I messed around with it during the CAD section, I never really felt comfortable with it.  It is not overly intuitive coming from commerical parametric CAD software.  Also, importing parts from solidworks requires converting each part to VRML 1 files, which Solidworks can do, but when you have like 20 parts, all of which were mated in SolidWorks and which would have to be remated, it's kind of a hassle.  Seeing as how I got a decent animation in SolidWorks, I just decided to mess around a bit.  I tried to do an animation, but it kept hanging up on me, so I was like, enough.