Tetrixx – a Robot Development Kit Stefan Enderle, Stefan Sablatn¨og, Steffen Simon, Gerhard Kraetzschmar Neural Information Processing Department University of Ulm Phone: +49-731-502-4152, Fax: +49-731-502-4156 fsteve,stefan,simon,
[email protected]
Abstract
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Tetrixx
Tetrixx is a modular kit which consists of the following catCurrently, autonomous mobile robots become more and egories of compatible parts: more interesting in entertainment and education. The authors gained a lot of experience in performing robot build- Mechanical Parts These are the main building blocks consisting of mainly bars and plates. They are used to ing labs at schools, high-schools, and universities during build up a solid frame for a car, a walking robot, etc. several years. However, an adequate robot kit which is modThere are also wheels, axes, and gears. ular, easy-to-use, powerful, and inexpensive could not be found. This was the reason for developing Tetrixx. Electro-mechanical Parts These are motors, servomotors, switches, batteries, sensors, etc. which make a model move and react.
1 Introduction
Controller The robots brain consists of a micro-controller board holding different expansion boards used to control actuators and sensors.
Robot building labs (RBLs) are a good means to bring the Special Parts These are specialized bearings for particular interesting field of robotics to schools, high-schools, and parts, e.g. special sensors, pneumatic parts, and so on. universities. Taking part at an RBL the students learn a lot about mechanics, electronics, and programming. Addition2.1 Mechanical Parts ally, they have fun and learn to work in a team. Performing a lot of robot building labs with pupils, stu- The basic parts of the Tetrixx system are aluminium bars dents, and elderly people, we found that there is a gap be- with 6mm holes along all four sides and two M6 threads on tween the relatively cheap toy-like kits and the quite expen- the front and back side (see Fig. 1). Currently, there are bars sive off-the-shelf robots. The toy kits offer a good oppor- from 20mm to 200mm with up to 20 holes, respectively. tunity to start building robots, but they mostly support the control of only 2-3 motors and the same number of sensors. Off-the-shelf robots (see e.g. [1, 4, 5]) are completely built up, so typically only the programming of the robot is studied. On the controller side, there are some alternatives, e.g. the 6.270 board or the HandyBoard [3]. However, these boards can control only small motors and are not very expandable. Of course, they come without mechanical parts, so you have to use a toy-kit or you must saw your own parts in your garage. Building our own RoboCup-robots from scratch [2], the authors gained a lot of experience about reasonable meFigure 1: Mechanical parts chanical concepts and controller architectures for a usable Either two bars can be solidly mounted or a plate can be robot development kit. Thus, we decided to develop the robot kit “Tetrixx” and to provide it to schools and univer- attached to a bar by putting a screw thru a hole and mounting it to the frontal thread of the other bar. Two parts can sities.
also be bolted together using a screw and a nut. The plates are also given in different lengths and widths up to 200mm x 200mm, currently. Other mechanical parts are wheels, casterwheels, axes, and gears (see Fig. 2). They are used to implement dynamic models which can be driven by motors as shown in the next section.
Figure 4: Switches, sonar sensors, and infrared sensors with their bearings kit, we developed a controller board which is both powerful and easy-to-handle. In Figure 5, you can see the controller board and the mini expansion board on top of it. Figure 2: Wheels, casterwheels, axes, and gears
2.2 Electro-Mechanical Parts In order to make a model move, motors are needed. There are several kinds of motors for different tasks, like DC motors, servo motors, and stepper motors. Tetrixx supports all categories by providing the respective bearings (see Fig. 3).
Figure 5: Controller board with mini expansion board on a Tetrixx plate The controller board consists of a Siemens C165 controller with 32KB RAM and 128KB flash memory. It can be programmed via a serial link and then runs autonomously without the host computer. The controller board runs the main program which uses the expansion board(s) to control the connected devices. There can be up to 64 expansion boards on top of a controller board and the controller can Figure 3: DC motor, stepper motor, and servo motor with detect which expansion boards are mounted. Currently, there exist two types of expansion boards: their bearings the mini-expansion-board and the servo board. The miniWhen building robots, it is necessary to make them able expansion-board is a starter board which controls two DC to gather information about their environment. This can be motors with 4A, four servo motors, eight LEDs, eight digidone by mounting simple switches signalling bumps to ob- tal and eight analog inputs. The servo board can control 16 stacles, or by adding distance measuring devices like in- servo motors. Expansion boards for sonar sensors [6], stepper motors, frared or sonar sensors. With the Tetrixx bearings for sensors (see Fig. 4) it is easy to mount different sensors to an and stronger motors are under development. existing model.
2.4 2.3 Controller Obviously, the motors and sensors presented in the last section must be driven by a micro-controller. For the Tetrixx
Special Parts
All parts presented above can be used quite generally in a lot of models, like robots. However, there are applications which need specialized parts for very specific tasks. For
example, sometimes ball bearings are needed since the friction of the axes in the aluminium parts is to high. Or, a pneumatic system (e.g. a kicker for RoboCup robots) has to be controled. Tetrixx offers a lot of parts and bearings which can also be constructed and manufactured on demand.
3.3
Robot Arm
The robot-arm is a student work with three degrees of freedom. It can rotate left-right and has a “shoulder”- and an “elbow”-joint. The robot-arm is also controlled by the servo-expansion board.
3 Experiments In order to demonstrate the feasibility of the Tetrixx parts and controller boards, we developed some prototypical robot applications. There are two mobile robots (a differential drive robot and a six-legged walking robot) and a 3 DoF robot-arm.
3.1 Differential Drive Robot The first mobile robot is a car with two independently driven wheels and a caster wheel. The mini-expansionboard drives the two motors as well as three infrared sensors. The sensors are used for a simple collision avoidance behaviour.
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Conclusion
The authors presented Tetrixx, a kit for developing autonomous mobile robots. The kit consists of solid mechanical parts, electro-mechanical parts, and a powerful modular controller. The Tetrixx kit proved to be an appropriate tool for robot development. It will be used in our future educational classes and labs in schools and at the university. The kits will be available end of 2000. For more information about Tetrixx, feel free to visit the Tetrixx website at www.tetrixx.de.
References [1] ActivMedia. Pioneer 1 Operation Manual. RWI, Jaffrey, NH, 1996. [2] Stefan Enderle. The sparrow 99 robot. Technical report, University of Ulm, 1999. internal report.
3.2 Spider
[3] HandyBoard. 1998. http://lcs.www.media.mit.edu/groups/ el/Projects/handy-board/index.html.
With the “Spider”, we wanted to investigate the problem [4] K-Team. http://www.k-team.com. of controlling 12 servo motors independently. This is done [5] Nomadic. http://www.robots.com. by the servo-expansion board which would allow for four more servo motors (und thus implementing a real spider [6] POLAROID. Ultrasonic Ranging System. Polaroid Corporation, 784 Memorial Drive, Cambridge, MA 02139, 1991. with eight legs).
