Saturday, January 5, 2013

dad stuff

J got a Lego Mindstorms NXT robotics kit for Christmas (he mostly paid for it himself by the sale of some older toys), and while Anna was off somewhere, we spent a day building the first couple projects.

It turns out that robots are kind of a pain in the ass. We built the beginning robot,  a plastic-ball-shooter that has treads instead of wheels, and I figured it would be easy to just have it rotate in place to different angles and shoot down Lego mini-figures. Alas, turning a treaded robot in place is so tricky it's not even part of the exercise. I'm not actually sure you can do it with Mindstorms, because you want the two sides to move simultaneously in opposite directions, and I didn't see how to do that.

Either way, you're doing a lot of trial and error, because your unit of movement is "rotations of the motor," and good luck figuring that out with treads. (In real life, of course, you make one robot, figure out how to turn it a fraction, then store that as a "turn X degrees left" instruction so you don't have to do it again. But that was proving challenging.)

He did learn about the degrees of a circle, though, back when I thought those might be useful for programming the robot.

A few days later, something came up and I started to tell him how you can quantify the likelihood of certain events, and it's called probability.
"Chris, you're being silly, there's no such thing as probability!"


I fetched some dice, and theatrically started explaining.

"Okay, how many sides to a die?"

He squealed and ran away. (He's been going through one of his periods with lots of squealing and hiding, sometimes for fun, sometimes as part of freaking out.)

As he ran away, I called out, "Probabilities are fractions!", and he laughed as he closed his door.
We played a game for a little while where he would come out, I would start explaining again, and he would squeal and run back into his room. Then I stopped playing, and he came over.
"Uh, Chris? I'm not sure if I want to learn probability but I'll learn it with you if you want me to. It might be interesting."
After I took a moment to melt from how sweet that was, we went through probabilities as fractions, the odds of rolling less than 3 on a d6, more than 7 on a d20, etc. and the odds of rolling 2 3s in a row. I screwed up the additive probability, though: on a d6, obviously you have a 1/6 chance of rolling a 1, and the odds of rolling a 1 increase with more rolls, but not in the naive way I was thinking, because otherwise you would have a 6/6 (100%) chance of rolling a 1 after 6 rolls, and that is obviously wrong. So I will have to get a book and re-educate myself in a way that I can explain to J.

Then I said, "Okay, that's all I've got for now," because I don't want to go into lecture-mode, I want to have things be interesting and exploratory for him, and not only had I not thought about it, but apparently I was more rusty than I thought.

"Well, Chris. I can't believe that's all you can think of right now."

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