A demo of one way to make a sphere with a hole...

I will try and search back in previous posts but the crux of it is that sketchy physics has a hard time dealing with "voids" which means that tubes need to be modeled by grouping together strips running the length of the pipe (for nice seams use trapezoids) The more "round" you want the pipe the less wide you want the strips. (I typically use circles with 24 sides...48 even better). Make one strip, define it as a convex hull (or rectangle), copy rotate and then group together. Check this youtube link for a quick demo....http://www.youtube.com/watch?v=DL52inWDqKo

sketchup does not "do holes" that well. Essentially if you want to have a void in something you need to cut it into a set of convex hulls and then group them together. For a rectangular piece with a hole in it you can do this essentially by drawing "rays" from the center of the hole out at regular polar intervals....30 degrees lets say. Each slice is then made into a convex hull and then grouped. There are ways of "faking" it but this is the way to actually make Chris Phillips Sketchy Physics engine do the work.

This may seem an odd place to put this but as I have looked at the Ruby methods for rotation they seem to be laid out very similarly to quaternion calculation which seem to be all the rage in robots and rockets. In the space of one week the word emerged in a number of discussions I read or watched particularly with regard to ROS and android and the neat little robot coming out of http://www.willowgarage.com. Since these discussions have been slow lately (except for the gems from Mr. K) I thought I would throw this one out there for now and then follow it up with some models and questions. PS. The best place I have found so far about the topic is http://www.euclideanspace.com.

There are a number of different ways but I think using magnetism and some ruby scripting is probably what I have seen the most often. Positive magnetism attracts things that are set to magnetic and negative repels (or vica-versa). If you don't know anything about ruby scripting...now is a good time to start. There is also a routine called SPLIT that will cut things in half but it has its own set of issues.

I second Mr. K on the sense that middle schoolers might delve into the scripting anyway...(all those video game hours won't have been wasted). As you go through the installs on the school computers I suggest compiling a list of essential ruby scripts/plugins (webconsole for one) that should be installed with it. I also found that Notepad++ is a good open source (always important when budgets are involved) editor for things beyond Ruby. Though my classroom experience has been with technical college students I also have a middle schooler who I KNOW was prepared both for more programming and 3d at 5th grade than she was exposed (aside from the video games). See Snatch at MIT and Alice at Carnegie Mellon for good places to get them tied into simple programming. Upon installing sketchup if nothing else they then have access to Ruby which is almost as much of a gem as Mr. K.

One more unsolicited suggestion (and this one may be a stretch due to curriculum). Much of ruby works on the fact that vectors in 3d space have THREE components and for the most part the curriculum does not cover that until long into high school. The ruby command for cross product (the cross product of any two vectors in a plane yields the normal) and a little creativity should have the students talking in 3d coordinates and comprehending directional vectors in no time....No slight to my students but 5th graders are more malleable.

Best of luck with the project....its great to see this incredible resource Sketchcup and sketchy physics making out to those who must save the planet.

Congratulations! Ireland is proud. Hungary also I guess.

Nothing makes me smile as much as seeing a post from Chris Phillips (though of course I always wonder how much of what I have learned over the last year is now superfluous). I will love to see how all this relates to that crazy piano and drum kit posted and shared in the past. Good luck with the remodel...can't you just do it in sketchy physics, give everyone a VR hood and call it good?

Works like a charm! As always I am enthusiastically grateful!

Its on "my list" but I don't at present. I am trying to dive into jsquery, ruby, and python simultaneously
so I can force feed my kids (and students) some basic information like balls fall down, the stock market doesn't
"always" go up and humpty dumpty was pushed. (Insert your own facts here). I'm trying to take advantage of what they are doing out on http://www.khanacademy.org in terms of designing everything into HTML and jsQuery enhanced pages. Thanks heaps...the multi user/multi file input stuff was really dug by my students....I think I caught them NOT looking at their facebook pages for at least 5 minutes(:))

Does anyone have any insight into how to pause and then restart a simulation from inside of Ruby. Specifically I would like to pause the simulation and then get input from a webdialog. As usual all help is greatly appreciated. I am trying to gamify some knowledge quizzing for my kids and this appears to be the last piece which will make them earn the right to attempt the sketchy physics throw into the Bozo buckets.

This thread has a bit of a related discussion though it is a bit of a jury rig to have the c++
write and read from an intermediary file. I too am interested in blending sketchy physics with C++ with the only problem being my completely inadequate knowledge of....C++.

http://forums.sketchucation.com/viewtopic.php?f=61&t=35210

What an incredibly good explanation. I guess it is now time to go back and get rid of all of those $Variables in my scripts.(:))

Mr. K...I could muster some of what was requested but this generated more questions than answers. Could you also add in some insight on how the definitions of what is attached to what are stored in the data structures(connects to ???). I am trying to learn Ruby both as it works in sketchup but also more powerfully in how it works in Sketchy Physics. Thanks heaps.

I both love the idea and can attest that it worked pretty slick between Central Wisconsin USA and Southern The Netherlands. Blox has some pretty intricate models and it was possible to have substantiative discussions regarding them. (not that I was any help).

http://forums.sketchucation.com/viewtopic.php?f=61&t=37533

Bjorn...I am in complete agreement however offer this contrary view to all of you multilingual Scandinavians and Europeans. Just as knowing at least two languages makes one in many ways better at both I do see a value in knowing at least two sets of units. The unfortunate part for most Americans is that we struggle at even knowing one. My favorite thing about the metric system however is that it makes it easy to remember how far it is around the globe (about). How many Metric first people can actually tie it all back to the French pulling a proverbial string from the north pole through Paris to the equator and "calling it 10,000,000 metres? One of most favorite fun facts. Enjoy the coming sunshine.

I have struggled for 10 years to get my college students to respect the units. Little did I know that I had the ruby slippers inside the machine. I presume someone collects the "blown units" stories so here is one related. A son of a friend's first job when involved in the International Space Station was to figure out how to make the 4 prong power receptacle on one country's module accept the 3 prong plug from the other partner. I will digest your most thorough and excellent post and move onto the music portion of the sketchy physics show.

I have been following the discussions regarding frame rates, physics time steps, and the fact that the Physics Engine is not perfect and finally took some time to tweak my settings to get a free falling object in a metric world to behave like it would in that theoretical "vacuum".
This was sparked of late by this question posted on http://www.khanacademy.org in the physics sections.
"A ball is launched with a horizontal velocity of 3.2 m/s. How long will it be until its velocity doubles". (about 0.6 seconds...I think). Anywho, using Sketchy Physics 3.2 and setting linear damping to 0.0 I ended up needing to set gravity to 4.38 in order to get the correct vertical velocities for the first 4 seconds. (-9.8, -19.6, ...). Curiously, I also had to multiply my initial velocity by the same factor,4.38, to get everything to behave "correctly". This was true whether my frame rate was set to 3 (aka 20 frames = 60 physics steps of 1/60th sec) or 1 (60 frames = 60 physics steps of 1/60th sec). Does anyone have any insight on this.

may25h.skp

I can see great potential in this one especially for making transparent "flipbooks" in PNG format for overlaying on a sketchup model.

http://www.pencil-animation.org