IEEE SPECTRUM
By Stephen Cass / May 2006
Vex Robotics Starter Kit
US $300
http://www.vexrobotics.com
Either you think building robots is cool, or you don't. But if you do, then you'll love the Vex Robotics Design System, a line of robot construction kits and accessories from RadioShack Corp., headquartered in Fort Worth, Texas.
RadioShack developed the Vex system in collaboration with Carnegie Mellon University's Robotics Institute, in Pittsburgh, and the organizers of an international high school robotics competition sponsored by FIRST (For Inspiration and Recognition in Science and Technology), a nonprofit organization based in Manchester, N.H. While the kit's target audience is high school kids in classroom and lab settings, it is versatile enough to appeal to a much wider audience.
I tried out the Vex Robotics Starter Kit, which has more than 500 pieces. What appealed to me right off the bat was that while Vex robots do use plastic for wheels and gears, they are constructed mostly from metal struts, axles, and plates, making them much more sturdy than many other robot kits. Motive force is provided by three motors that can rotate continuously clockwise or counterclockwise and one servo motor that moves forward and back through a 120-degree arc. These motors will be familiar to anyone who's ever built a remote-controlled plane or car--in fact, the Vex kit is compatible with most remote-controlled hobbyist motors--and they are versatile enough to enable a wide range of robot designs.
The motors are driven by a controller module, which in turn is powered by a battery pack. (A word of caution here: the Vex system eats batteries, so take the manufacturer's advice and invest in rechargeable batteries.) The controller module contains two PIC18F8520 microprocessors and bristles with input/output ports. Sixteen ports are shared among analog and digital input/output functions, and eight more are dedicated to driving motors. Each processor can perform 10 million instructions per second, and one of the processors can be programmed by users to control the robot while the other processor takes care of housekeeping tasks, such as looking after the controller's communications systems and sending the precisely timed electrical signals required to drive the motors. The communications role is particularly important, because the controller is normally hooked up to an FM radio receiver that takes commands from a human-operated six-channel remote control. The maximum operating range is about 35 to 40 meters.
It took me a couple of hours to build my first robot--a rectangular, four-wheeled creation dubbed SquareBot by RadioShack [see photo]--using the instructions that come with the Starter Kit. With the remote control, I could steer SquareBot forward and backward and make it spin on the spot (for a video of SquareBot in action, check out http://www.spectrum.ieee.org/squarebot.mov). But SquareBot is more than just a glorified remote-controlled car, as it is capable of some onboard autonomous behavior--if either the front or rear bumper switch detects a collision, the controller module will override instructions from the remote control and cut power to the motors for a few seconds, giving the operator a chance to rethink.
The controller module can also be configured to use a basic, but fully autonomous, preinstalled program that enables a robot to feel its way around a room on its own. Although I stuck to what came with the Starter Kit, advanced users will want to buy the US $100 Programming Kit, which will allow them to write their own software and take full control of the hardware, where 32 kilobytes of program space are available. Six extra ports are provided on the controller module to service real-time hardware interrupts (which suspend normal program activities and invoke specified subroutines to handle various events); this makes the Vex system a candidate for use in serious robotics research.
Only four sensors come with the Starter Kit: two rugged bumper switches and two more sensitive--but more delicate--microswitches intended for detecting such things as whether a gripper has grasped an object. The paucity of sensors is understandable, given that inexperienced or young users will likely be controlling the robot visually with the remote control, but advanced users will soon find themselves looking for such Vex accessories as the $20 light sensor and the $30 ultrasonic range finder. While there is an official Web site at http://www.vexrobotics.comthat features the various add-ons, including items like tank-track sets, real gearheads will want to check out http://www.vexlabs.com, where the Greenville, Texas-based Innovation First Inc.--which engineered the Vex system for RadioShack--offers prototype accessory sets that have not yet been adopted as part of the official Vex line.
In fact, it's pretty easy to incorporate all sorts of additional equipment into a Vex robot, including components not specifically designed for the Vex system, such as the remote-control hobbyist motors mentioned above; electrically interfacing many non-Vex components to the controller can be done relatively easily through the many input/output ports provided. This flexibility makes Vex markedly different from that other popular general-purpose robot construction system, Lego Mindstorms. The Lego system can be used only with parts and sensors specifically built for or modified to work with the Mindstorms equivalent of the Vex controller module. Also, because Vex robots are built using screws and metal plates, mechanically attaching various off-the-shelf sensors or other devices is pretty straightforward--again in contrast to Lego, whose plastic bricks and spars make it difficult to secure non-Lego components.
I did have two nits. First, the included documentation provides a guide to building a SquareBot robot, and its careful, step-by-step instructions and explanations will make the job of instructors helping students using the kit much easier. However, while general building principles are often outlined, the documentation doesn't give any specific instructions for building other robots. More example designs would help beginners--and even experienced robot builders unfamiliar with the system--get a better grasp of how the wide range of pieces that come in the Starter Kit can be employed, before they tackle their own creations.
My other nit was with the packaging. Many of the Vex parts come packed on top of other parts in a single large piece of Styrofoam--and some parts are packed into the underside of the Styrofoam container. This makes it impracticable to have the packaging double as a storage box (as can be done with Lego Mindstorms), and Vex users will have to invest in something like a fishing tackle box if they don't want to lose parts or spend forever trying to distinguish one type of screw from another.
But the bottom line is that the Vex system is fun to use, and it adroitly fills a gap between the simple, but somewhat constrained, world of robotics kits such as Lego's on the one hand, and the powerful, but often bewilderingly complex, world of scratch-built robots on the other. I expect it to become a familiar sight in high school and university labs, as well as in the garages of home-brew robot builders.
