Feb 1: Robot Updates

Progress continues on the fire fighting robots.

How much work did it take to get to this point?

  • work started Nov 28
  • we’ve met for 27 class days since then
  • which amounts to approximately 22 hours of work

The biggest mechanical obstacle that remains for the students is finding a fan that will extinguish a candle from anything but point-blank distance.

Teams of 2 seems ideal — everyone has an important role to play, they can work in parallel some tasks, yet both team members knows what’s going on with all parts of the robot.

The Gantt Chart project plans I added as part of the project aren’t helpful. They’re busy work as far as the kids are concerned. Plus, the students are novice enough that they’re poor estimators of their ability to make progress. Next year, I may drop this part.

I’m considering next year having a midterm demo day with a set of performance targets the bots have to hit by that date. For example, these bots should be able to navigate a hallway and make one turn. This year, we held a design review at the midterm (a little over a week ago), which went well from my point of view though I don’t think the kids got too much from it.

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Jan. 30: Buoyancy Activity

How does the reading on a force probe change as you submerge a weight under water? And what does that have to do with buoyancy?

What follows are pictures of an activity we’ll do in class on Thursday. With a student out of school for a week, I needed a way for her to participate in the activity at a distance. This sequence follows the activity nearly frame-for-frame.

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Hang a 100g mass from a force probe. Confirm it reads 1N.

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Yep, 100g and (approx.) 1N.

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The weight is suspended above the water and the force probe reads 1N.

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Half-submerged and the force probe reads a little under 1N. Clearly the water’s providing some type of upward force, taking some of the weight off the string.

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Fully submerged and we’re reading about 0.9N — that’s about a 10% drop in weight on the force probe.

 

Day 10: Braitenberg Vehicle Demo Day

Thursday, 21 September 2017

The Braitenberg Vehicles are done and today we demo’d them as a group. The bots show varied chassis styles, though the electronics are functionally the same:

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We learned to breadboard! Super cool experience that I’m sure will pay off later as we develop our own projects.

We learned about basic circuit components! Resistors, photoresistors, jumper wires, transistors, and diodes are all in our wheelhouses now.

We learned how motors work! Swapping the connection results in a backwards-spinning motor. So cool!

We strengthened troubleshooting skills! Man, those breadboard holes are close together. You wouldn’t believe how often that messed us up.

I only managed to record one bot during demo time — this guy runs from the light, which Braitenberg dubbed “Fear”:

Note to self for next year:

  • Consider the ways that a cardboard box can be a structurally sound chassis and show the kids some of those methods. A flat piece of cardboard is iffy at best and electrical tape is way too stretchy.
  • Locate a room that can be made quite dark. The classroom is way too bright to get the bots to turn toward a flashlight spot. For quick tests, it’s important to have a space.
  • Invest in a few flashlights whose beams can be focused better than the ones I have. A broad beam tends to hit both photoresistors and the bot doesn’t turn (though fixing that problem is a fun design challenge, too, so maybe not). One student was driving his bot with a laser at the demo — does that method have long-term benefits worth investigating?
  • Is it possible to use the same motors that come in the Ardumoto Shield Kit? They’ll be central to our line follower bot for the next project, so it’d be nice to reuse more materials to save costs and keep with familiar parts.
  • Do I want to organize demo day in a more rigorous format? I had the kids share with another person, then we drove our vehicles around a dark-ish room for awhile and had fun reveling in the finished project, and finally we reflected on the experience.

EDIT: Parts List

Circuit diagram and explanation of how it works.

Day 6: We’re Rolling!

Friday, 15 September 2017

Our Braitenberg bots are coming along! After a change of course from what I wrote a few days ago — turns out the particular op amp I was using put out too little current to drive the motors — the new circuits are now tracking the light properly.

It’s subtle but can you see how that last bot turns away from the light? The student who built that one had an interesting time figuring out why his robot ran from the light. He loved learning that cross-wiring the left photo resistor with the right motor would give him the light-seeking behavior he wanted.

Today, we spent much of the period building robot chassis out of cardboard boxes because that’s what we have in abundance.

A Braitenberg vehicle built to the same specs as we use in the video requires the following parts:

  • breadboard
  • hook up wire
  • 2 NPN transistors
  • 2 diodes
  • 2 photo resistors
  • 2 geared motors with wheels (we’re using these from Solarbotics)
  • a 9 volt battery with a battery connector

We’ll build for a few more days next week at which time the students will submit a project writeup. I’ve asked them to submit video of their robot performing all its functions, schematics, and a reflection.

I’m so glad that all the student Braitenbergs are working as expected and all that’s left is to finish the chassis. The students have learned breadboarding, how photo resistors work, and how basic circuit wiring. I think that’s great progress in a week of classes. We weren’t ready to learn transistors and diodes, in my opinion. I think between those components and the missteps on starting with op amps, this project was unnecessarily complex. So, in retrospect, I might not start the year with Braitenberg, though it’s definitely a keeper.

Day 2: Breadboarding+

Monday, 11 September 2017

UPDATE: See the end for an easier way to build a simple Braitenberg Vehicle.

Did you know a robot can show aggression — charging forward toward light? Or fear — running away from light? Even exploration and love? The emoting robot is based on the work of Valentino Braitenberg and we’re putting some together in robotics class.

The above video is absolutely beautiful in the same fashion as Vi Hart’s math musings. The video comes out of an Instructable on building Braitenberg Vehicles. Unfortunately, the details on wiring it up were lacking:

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Ugh, you mean I gotta refresh my memory on all this stuff?

That’s when I found breadboard diagramming software and wrote the instructions myself: Wiring a Braitenberg Vehicle. This stuff is totally untested, so I’m seriously crossing my fingers over here that it’s gonna work.

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Untested breadboard layout for a Braitenberg Vehicle.

My students have next to no electronics experience (and I have minimal — this is the first time I’ve used an op amp, for instance), so I am pleased at the step-by-step way I built it up. I’m hoping they’ll learn:

  • how the rows and columns are connected on breadboards
  • how a photoresistor changes resistance with the amount of light
  • how the Braitenberg Vehicle can demonstrate different emotions with subtly different wiring
  • how to get two wheels turning in the same direction

The Braitenberg Vehicle is a cool concept and I highly encourage you to watch the video, even if you’re not inclined toward robotics.

UPDATE 9/13:

Ugh, so sad, after hours of debugging, I’ve decided that the op amp isn’t generating enough output current to drive the motors well (maybe with different gearing I’d be good). When I shined a flashlight directly on the photoresistor, the motor let out a whine and only spun if I nudged the wheel.

So, I was thrilled when a student told me he’d found plans that use a transistor. The drawback is that we lose the functionality of speeding up or slowing down with the amount of light.

Day 1: Motors

Friday, 8 September 2017

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Day 1 of robotics with juniors and seniors. I handed them geared DC motors and battery packs.

“Make the motor go forwards, backwards, fast, and slow.”

I chose this activity because I’d heard my students had all levels of experience and this would be a fast way to sort them. And the kids really did run the gamut — some had a motor running within seconds and others took awhile to find the connection points on the motors.

One kid told me he and his friend want to build a golf cart driving robot that can be placed in an unmodified cart.

I’m at a new school and have a new courseload: Physics I (a conceptual physics course mostly for 9th graders) and Robotics. Come along for the school year told through pictures from 180ish school days.