Tuesday, October 21, 2014

A case for family tandems

Did you enjoy my previous embedded WolframCloud project?  Yes?  Great!  Let's do it again, this time with a tandem bicycle.

One of the nice things about tandems for kids is that they are (theoretically) never outgrown.  To show how this works, I put together another wolframcloud project.

I made a rough model for a kid growing over time.  Mathematica has data for childrens' sizes (== girls growth chart, or just go to wolframalpha.com and type the same).  I scaled all body parts linearly for the graphic.  Our kids' thighs are relatively a bit short compared to Jill's, but this is pretty minor.  All other bike-related body dimensions scale quite linearly.

I'm drawing the frame using an extension of the code I wrote last time.  Somehow, Mathematica doesn't have bike frame geometries built in.  I'm sure we'll address this oversight soon.  Perhaps we could use image processing methods (accounting for image distortion away from the center of the image) to grab the numbers.

In the tandem embedded graphic, the kid's age can be adjusted, from tiny 4 year old to 14, or basically fully grown.  Note that Clara's face doesn't age along with her digital age.  We don't have a function for that built in (yet!), and anyway it would freak me out to see the results. Also, my apologies for not giving her a helmet.  As digital kid gets older, you can adjust the saddle height and position of cranks to find a nice fit.

You may find some combinations that cause the kid's knees to bend the wrong way.  I didn't specify which solution for the quadratic equation (someday I might fix this), so Mathematica sometimes grabs the nonphysical one.

The handlebars can be either a swept back bar (current) or drop bars.  As the kid gets bigger, drop bars enable the kid to stretch out more comfortably, especially if you use the drop position (3).  If you do that when the kid is very young, she can't reach all positions on the bars.  That would be really dangerous in the real world!

If iframe isn't working try our cloud directly.

One other fun thing about tandems is that daddy and kid have to pedal at the same cadence ( technically not true, but changing this requires using different sized chainrings on the timing cranks.  This is a bad idea because either (a) the kid pedals slower, but needs to push harder or (b) the kid pedals faster.  Neither is a good idea in my opinion.).

Despite having the same cadence, our foot speeds are different.  Right now, the kid's cranks are 120 mm long, while daddy's are 170.  This means my feet are moving about 1.4 times faster than the kid's.  When the kidback cranks are no longer needed, both sets of cranks will be the same length (not modeled).

Check out more information about the Wolfram Cloud.

Thursday, October 9, 2014

return of the bunny

Clara turned 5 years old last month.  We continued the tradition of having birthday parties late morning (before mom and dad start to feel worn out).  She wanted cake and cupcakes, both with pink frosting, and a pinata.  
 Pinatas are way overbuilt these days.  Thankfully, a 6th grader came to the party and put some hurt into it [at the Wolfram Research summer party, we needed the biggest guy in the company to break it open after the kids failed to make a dent].  Clara was able to finish hers off.
 Not to be outdone in the growing up department, Janny asked to ride the tandem with me.  I lowered the saddle about an inch, and off we went up and down the street.  We're still a bit hesitant to take her far on the thing, since she's our "fall out of a chair for no reason" kid.  But watch out next spring!
 I guess that I forgot to write about the loss of Bunny during our Michigan vacation this summer.  Somehow bunny jumped out of the car between Aunt Jan's house and Boyne Mountain.  Clara was really hurt by the loss.  Jill bought a different version (I think it was an owl?  I haven't seen it in weeks) but it didn't take.

Then, Ebay!  And Clara has New Bunny.  She loves it, but not with the same affection as the original Bunny.  Sometimes, she forgets to bring it to bed.  I guess you never get over your first love, no matter how young you lose it.
 We let Clara use the camera for a morning.  Have you ever wondered what the view from inside the trailer is like?  Here you go!
There are 2 boys interested in marrying Clara [I say, we'll see].  Janny recently told me that she doesn't want to marry anyone when she grows up.  However, in a rather sporting gesture, Clara offered one of the boys, and apparently Janny accepted.  So that's all settled.