Mini Guidance: Sensor Helps LEGO Fans Navigate Robotic Creations

July 25, 2011  - By
A Google Street Car in miniature uses Dexter Industries’ dGPS sensor (Photo courtesy of Mark Crosbie.)

A Google Street Car in miniature uses Dexter Industries’ dGPS sensor (Photo courtesy of Mark Crosbie.)

Aspiring engineers, take note. A company dedicated to building robotic sensors for the LEGO Mindstorms NXT system has released a GPS sensor, and a workbook on how to use it.

John Cole, founder of Dexter Industries, explains that his products are intended for the education market, and are “for engineers, scientists, and those aspiring to be.”

“A few months ago, we developed a GPS sensor for the educational market, called the dGPS,” Cole said. The sensor is sold separately, as a third-party product for the LEGO Mindstorms kit.

The dGPS sensor provides GPS coordinate information to a robot and calculates navigation information. It provides latitude, longitude, time, speed, and heading. It also has powerful navigational calculators that can be used to navigate to target coordinates.

The dGPS sensor uses a Skytraq module. The LEGO NXT has limited computing capability and can’t interface directly with a GPS module, so Dexter Industries developed a micro-controller and software that translates and checks the signal from the GPS, and also performs additional calculations and functions for navigational purposes.


Photo courtesy of Mark Crosbie

“For example, in addition to the standard GPRMC string that comes from a GPS chip, our dGPS sensor can receive destination coordinates from the user and calculate distance to destination and angle to destination so they can be matched against a compass,” Cole said. “Also, because robots of this scale are usually traveling below 15 mph, we developed a more accurate compass function that works on the smaller, slower scale.”

The dGPS hooks directly into any of the four sensor ports on the NXT and can be programmed in NXT-G, RobotC, and LeJOS programming languages.

Cole became interested in the Mindstorms system in 2005 while in graduate school. “It’s an incredible robotics kit that really fits with educational curriculums on the high school and junior high levels. The kit lowers the entrance requirements to get started [in engineering], and because it’s based on LEGO, students are usually comfortable getting started with it. It’s deceptively simple, though; the Mindstorms robot can be used to do some pretty powerful stuff.”

Cole’s company had developed a few other sensors for education, including a solar kit and a pressure and temperature sensor, but focused on developing a GPS sensor, Cole said, because it “would be really fun for kids to start using. In particular, things like autonomous vehicles and mapping vehicles have been really exciting to develop and build with this sensor.”

Not Just for Kids. Mark Crosbie, an adult fan of LEGO (the hobbyists refer to themselves as AFOLs), has built a miniature version of the Google street car that roams the streets to photograph them for Google Maps. The car provides panoramic views from various positions along the streets it travels; data is then made accessible through the Street View feature of Google Maps.

Crosbie created his Street View car using Dexter Industries’ dGPS sensor to record coordinates as it drives along. “John has been very supportive of the project, providing great technical assistance to me as I used his sensor,” Crosbie said.

The idea for a miniature Google street car came to Crosbie when he was playing with the dGPS sensor. “I realized that if I combined this sensor with a robust chassis and a camera then I’d have a LEGO version of the famous Google Street View car. And what if I could then upload the pictures into Google Earth,” writes Crosbie on his website. “It all seemed so easy… How wrong I was!”

As Crosbie explains, his miniature Street View car is controlled manually using a PSPNx sensor to receive commands from any standard PSP game controller — the user presses the triangle button on the controller to capture an image and log the GPS coordinates. The cameras provided the biggest challenge. “The keyfob cameras are very temperamental and difficult to mount into standard LEGO dimensions,” he said.

“Every time an image is captured, the current latitude and longitude are recorded from the dGPS,” Crosbie explains. “The NXT creates a KML format file in the flash file system, which is then uploaded from the NXT to a PC. Opening the KML file in Google Earth shows the path that the car drove, and also has placemarks for every picture you took along the way. Click on the placemark to see the picture.”

Despite technical challenges outlined in his blog, Crosbie is undeterred, and working on another prototype. “I’m already hard at work on version 2.0 of the Street View car for a big event later this year.”

How-to Book. Besides hardware, Dexter Industries offers educational support material. “Just last week, we released a book that introduces middle school and high school students to GPS, and how to develop robots that use the GPS,” Cole said.

The book, Beginning GPS for NXT Robots, provides students with an introduction to the basics of GPS, and includes hands-on activities and tutorials on how to use the features of the dGPS sensor with the robots.

“This workbook was written to bring the GPS system to life and help students understand it, explore it, and find new ways to use it,” Cole said.

4-H program’s GPS/GIS program has started to use the company’s sensors in its curriculum, Cole said, because the sensors hook directly into the NXT robots.

The ION Mini-Urban Challenge, in which high school students compete to navigate a LEGO robotic car through a miniature city, don’t use GPS sensors. Students are provided with a kit that contains six other sensors that detect things such as light, color, and sound.

“We would love to be part of the ION challenge and we’ve tried contacting the organizers just recently,” Cole said. “It would be a great fit to get some students using the GPS in a way that really gets kids engaged in GPS/GIS development.”


A Google Street Car in miniature uses Dexter Industries’ dGPS sensor (Photo courtesy of Mark Crosbie.)


A street-view photo captured from the on-board cameras of the mini car. (Photos courtesy of Mark Crosbie.)



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