ROBOTMAK3RS Blog

Some time ago, HiTechnic kindly sent me one of its very useful acceleration sensors . This weekend, I finally have found time to experiment with the sensor in using it for collision detection: Do not forget to check out Brian Davis' and Steve Hassenplug's great discussion on NXT sensors in general and the acceleration sensor in particular, too.

The on-board camera makes for a fun video. More details here .

About a year ago, I blogged about datalogging acceleration profiles of several rides at Walt Disney World, using the HiTechnic accelerometer and the NXT. Well the story doesn't end there. I mentioned this information on a Disney fan site, where not only were people interested in the results, but asked for more - particularly a ride called Rockin' Rollercoaster, which uses a linear motor to shoot the train forward at high acceleration straight into a loop. The problem was this coaster exceeds the 2.5 G limit of the Hitechnic accelerometer, so I decided to try again, using the "Version 3" accelerometer from Mindsensors , that can reportedly measure up to 10 G's. Mindsensors very graciously providing me with a unit to test, and I thought this would be the ideal way to do it... subjecting the hardware (& myself) to high-G rides, and review a sensor in the process. The Mindsensors newest accelerometer was mentioned here back in August: it has a user-selectable ...

The first RCX climber was slow and unbalanced. The second NXT version was much faster, but still not very stable since it used the same techniques. This third version is a new design, made so that it will automatically balance itself on one axis. Balance on the other axis is achieved with an acceleration sensor. Imagine a line from the left wheels to the right wheels, through the middle of the robot. On this line, the robot tilts when it gets unbalanced. Unlike in the older versions, the main weight is now below this line. This means that it will keep itself balanced without help. However, there is another possibility for the climber to crash. That happens when either of the sides loses a bit of grip or if both sides do not go as fast as each other. You can correct this error by making one of the sides go slower, so it will achieve balance again. You would only have to know how big the error is, and in what direction. This is what the Mindsensors Acceleration sensor measures. A relat...

Well, it’s been far too long since I’ve blogged… well, anything . So I wanted to drop a quick line to mention three interesting datalogging examples I’ve hit upon during the last few months. In some cases, these are only ideas to be built upon, but they should give you food for thought on datalogging with the NXT. All these images are up in my Brickshelf gallery if you want to look – plus more. First, I was contacted by someone who wanted to know if it was possible to use the NXT to log the accelerations of a Hulahoop. So I said “I don’t know”… and tried it. The first task was trying to get a semi-balanced hoop with the weight of the NXT. So I used the b est thing I could to counterbalance an NXT… another NXT. Using duct tape (a lot of duct tape) I taped one NXT with a Hitechnic accelerometer to one side, and another NXT to the other side as a counterbalance. OK, now the next problem… I can’t Hula-hoop. At all. And a hula-hoop with a dozen AA batteries duct-taped to it isn’t the easies...

One of the things that has come up recently with regards to NXT-G v2.0 and datalogging is the speed that information can be logged. It seems the custom logging option under NXT-G v2.0 may be “slow”, in that it only logs somewhere between 10 and 100 readings every second (reports vary wildly, and until I test it myself I’m in no position to speak on this). Readers have pointed out, quite correctly, that NXT-G is not the fastest option for this. Robolab, for instance, is faster, and other offerings such as RobotC and pbLua are blazingly fast. But before everyone complains about this “new feature”, consider two other important points. First is ease of use. It seems that with NXT-G v2.0, LEGO Education will be releasing a version that has a lot of the datalogging handled for the student (or the teacher), making it easier to get and process data. That may require a slightly slower acquisition rate, but it may be more than worth it to some folks, especially if it provdes built-in smoothing,...

So what do you do if you're taking a family trip to Disney World, and you're me? Take your NXT of course! As a physicist, I've always been curious (read: obsessed) with things like the acceleration on roller coasters. So, on a recent trip to Walt Disney World in Florida I took an NXT with a field-ready datalogging program & a Hitechnic 3-axis accelerometer attached. In the picture at left, you can see the NXT with me on Expedition Everest... OK, actually what you see is a picture of me screaming like a little girl with one hand raised, as the other crushes the NXT into the seat beside me. But it's there, trust me. Previously I had datalogged by just grabbing a reading and storing it in a file as quickly as possible. But for a 5 minute ride the resulting file would be large - so large that I could only record one or two rides a day. Instead, the program stores the average value of the three axis data, with the sampling interval selected by the user at start-up. The...

So what happens when you let a physicist loose with an acceleration sensor? They find something to measure of course! I’ve been fortunate enough to test several sensors, including the HiTechnic acceleration sensor. This is a 3-axis accelerometer that can register up to 2.5 G’s along each axis with a fairly high resolution. I used it for a couple of “standard” robotics-type applications, like vehicles that try to roll up hill, etc., but what originally drew my attention to the RCX, years ago, was its ability to function as a cheap datalogger. So I wrote up a simple NXT-G program that allows me to log data from the sensor to the NXT file system on command: the result is a compact and very rugged datalogger, suitable for measuring accelerations almost anywhere. As an example, I duct taped the sensor to my tailbone, and went out back to play on the swings. The graph shows the results. The red line is the side-to-side acceleration (minimal, as I was trying to swing in a straight line), whil...