Over The Edge: abusing "toy" hardware in new (wet) ways
Someday, the hardware police are going to come and take away my toys, citing me for criminal abuse. Until then, I'll continue to see what an NXT can handle... and what I can learn in the process.On a recent trip to Niagara Falls, I was fascinated again with this huge, impressive natural feature. And thinking about the foolhardy souls that over the years have tried to survive going over the falls in a barrel, I did what was natural for me - thought about the NXT doing it. Of course, getting permission to throw something over Niagara Falls is unlikely to happen... and it's dangerous, and retrieving it would be extremely difficult. But I could certainly do some test runs... so was born the "NXT in a barrel".
I used an NXT slid into a 4" PVC pipe segment, sealed tightly at either end with re
movable closeout plugs. To keep it from bouncing around inside, I used a hot-wire cutter to shape foam "bulkheads" to support and lock the NXT into place within the tube, and attached a 50' line to retrieve it after. Then I went to a small local dam, started it, sealed it tightly, took a deep breath... and threw it over.The NXT logged two sensors 30 times a second, a 3-axis accelerometer from Mindsensors, and the LEGO sound sensor. Above the dam it floated tranquilly, quietly, and approached th
e edge. During the fall, the sound level went up only a little, but the accelerometer clearly registered a freefall as it went over the edge. Then there's a sharp acceleration as the pipe hits the rocky bottom end-on, and the noise level suddenly spikes up, as water crashes down on top of the PVC pipe and the unit is tossed and turned at the sloped, rocky base of the falls. Then suddenly it quiets down, bouncing in the tailrace in the fast-moving water below the waterfall.All in all, this gave me yet another chance to "live vicariously" and understand something that I have no (safe) way of experiencing myself. Could I scale this up? Certainly (& I'm planning to, in a couple of different ways). Could this be used as a teaching tool? Absolutely, in so many ways. Total cost beyond the NXT was maybe $15 total for the plumbing, and programming was very easy.
Niagara Falls it's not... but it's as close as most of us are likely to get. Now excuse me, I've got to find a bigger waterfall...
Comments
Were do you keep getting these ideas? =)
No video? such a shame...
although I'm not sure I can handle the picture of an NXT going over the edge...Horror:D
Good job!
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I don't think I fully understand your graph though. You plot 'x fore/aft' and 'Net Accel'. I assume this data is somehow computed from the 3 axis accelerometer data, but could you give some more insight in what they exactly are and how they are computed?
AS: You're completely correct, it's a 3-axis accelerometer. To get the net acceleration (dark blue dataset), I take the data from each axis and square it, add it together, and take the square root: Net = sqrt( xaccel^2 + Yaccel^2 + Zaccel^2). That will be a measure of the total acceleration on the robot, regardless of how it happens to be oriented at the time. The "fore/aft" trace is the data from just one axis of the accelerometer - the one that was directed along the long axis of the cylinder. For this particular run, the cylinder went over almost exactly "bow first", and hit the bottom end-on, so the acceleration along that one axis was very distinctive. That didn't happen for every run (I did about 6), but for this run it was a very "clean" signal.
By looking closely at the 3-axis data, you can see when the cylinder rolls as well, but for such short runs and a well-balanced cylinder, that usually doesn't show much. Longer runs in a wave pool (OK, my in a pool making waves) need to be done next.