The Grinding of the Gears

We spent the last two weeks working on gears - showing the students how gears work, that they speed up or slow down, and that they let you trade off speed for torque (which we just called "power" - apologies to hard science majors). We then tried to get them to add gearing to NXT motors. As with the previous activities, we tried to let them figure out how to do it. I don't like to use the word "disaster", but the students were pretty frustrated by the end of class. We decided to extend the activity to the next week, giving them direct instruction about how to add gears, and preserving the cars that had been constructed.

I had thought, for many years, that adding gears to the output of NXT motors would be a big hassle. It turns out to be quite easy - all you need is to use a "lift arm" (bent beam) attached so that it gives you holes in horizontal or vertical alignment with the motor axle. The very simple framework pictured here lets you add three different pairs of gear sizes: 24:24, 8:40, or 12:36 (thick "knob" gears). Of course, the latter two can be applied to either reduce or increase speed.

So, we told the students to add the 24:24 gears to the motor, as pictured above, and measure how far the car goes in 5 seconds and see how well it climbs up a 30-degree ramp. (We have 350 cm (12 foot) tape measures for each group and are having them do all measurements in metric.) We then asked them to replace the gears with the 8:40 gears and repeat the experiments. They could choose whether to have a "race car" or "tow truck". I had expected that this would be easy for them - just pop the wheels and gears off, put on the other gears, and put the wheels back on. Nevertheless, most of them still had a lot of trouble. A few of them tried to put the wheels on the motor output, ignoring the gear. I'm not reporting this to chastise them - I think that they just weren't quite ready for this activity. After all, most of them had never seen a gear before this, much less tried to build anything with them.

After the last gears class, we had a meeting with the teachers to figure out what we could learn from the experience. We realized several things:

• Most of the students are not yet comfortable building with the parts. We tried to deal with this by giving them detailed instructions for building things.
  
• In trying to make it easy for the students to experiment with the gears, we'd reduced the activity to direct instruction - "build this, add that, do it this way" etc. They didn't have any opportunity to be creative, which is what had made the first classes so much fun and energizing.
• There had been no chance for them to present their work - another part that they'd enjoyed - since they were all building the same thing.
• Although they'd definitely learned about gears, it just wasn't fun - and we believe that there's no reason that these activities can't be fun.
  

We resolved that the next activity would focus entirely on building, with as much opportunity for creative design as possible. They're going to build bridges to help a family of batteries get across a river. More on that later.

There were some good things that we did which engaged them.

• They liked measuring how far their cars would go. We collected the distance measurements and they showed a great distribution. If we'd had more time, those numbers would have been great fodder for discussing why apparently identical experiments give different results.
  
• We used a ramp to demonstrate the speed vs. power trade-off. They all wanted to try their cars on it. Few of them could believe that their race car wouldn't go up the ramp even the slightest bit, no matter how many other race cars they saw stall.
  

The NXT Brick - Unplugged

The NXT 2.0 software includes new firmware (see previous post) that lets you create simple programs directly on your NXT brick - no computer required. I've prepared an exhaustive tutorial for your enjoyment.

Hardware, Software, and Firmware

Apologies if this post sounds like an advertisement for LEGO products...

To get set up for the LEGO Engineering program, the school bought the LEGO Education NXT kits - the standard 9797 set. We also bought a site license for the NXT Software 2.0, which (new in 2.0) includes "data logging" capabilities. That means that you can take measurements (using any of the sensors) over a period of time and record the data. You can then graph the data - either on the NXT or on a computer. I'm really looking forward to using these capabilities. Note that there's no difference in the NXT brick - it's just the software.

Firmware Version 1.28
With the NXT 2.0 software comes a firmware update, to version 1.26. But... don't install it. I heard from one of the attendees at our LEGO Engineering Conference that his NXT sometimes froze when doing line-following. The good news is that there's a firmware update (1.28) which he said fixed the problem. I highly recommend it. It has a very, very cool feature: you can do simple programming directly on the NXT brick - no computer required. I'll try to make a post about that feature.

Based on one person's experience, the 1.28 firmware seems to be compatible with the 1.0 NXT software - which is great! However, if you decide to try it, make sure that you have the older 1.05 firmware handy in case you need to revert - just in case.

One annoyance is that the firmware comes in a ".rar" file, an archive format like ".zip" or ".sit". I had never heard of it, which is saying something. On Windows, I'm told that WinZip, which you may already have, can unpack the file. If you don't have WinZip, the free utility 7-Zip will do it. On the Macintosh, a program called The Unarchiver will do the trick.

Charging Multiple NXT Bricks
I lied. The school didn't buy the standard 9797 kits. Those come with the rechargable battery (good) and a wall-wart style battery charger (bad). I hate wall warts. I especially hate the thought of 16 of them plugged into 5 or 6 power strips, plugged into another power strip. So, I had the school buy the W991501 8-Pack plus light sensor - you get a second light sensor and no battery charger.

So, how do we charge the batteries? Long ago, I started out as an electrical engineer and I still like to tinker. I built 3 "multi-chargers" that can each charge 5 NXT bricks. They take up way less space, have longer cords, and less wire tangling.