By Caleb DeGard and Dan DeGard
Keywords: Tutebot, mobile robot, Jones and Flynn, analog computer, LEGO Technics, electronics, tutorial, basic robot, educational robot
The construction and operation of a basic mobile robot called "Tutebot" is described. Lessons learned from the experience are included. The design of the robot follows instructions found in the book "Mobile Robots, Inspiration to Implementation", by J.L. Jones and A.M. Flynn (copyright 1993, A.K. Peters, Ltd.). The robot uses LEGO Techics for the chassis and powertrain, and an analog computer constructed using common electronic components found at Radio Shack stores.
Mobile robots are an interesting conglomeration of disciplines. Mechanical, electronic, optic, and computer sciences all are involved in the making of a mobile robot. It is our opinion that no finer technical learning opportunity can be found. Constructing and operating your own robot is inherently satisfying, and may likely lead to more advanced studies. Robotics is an excellent high-tech playground for technically-inclined adolescents and jaded mid-career engineers.
The primary text and reference used for this project was "Mobile Robots, Inspiration to Implementation", by J.L. Jones and A.M. Flynn (copyright 1993, A.K. Peters, Ltd.). This book contains the essential first help to constructing a working mobile robot. The robot constructed is named "Tutebot", an apt contraction of the two words "Tutorial Robot". In the preface, the purpose is stated as "to put together an expos on enough basic skills so that a generation of enthusiasts will not only widen their imaginations but also have the requisite tools to implement those dreams". The text has performed that purpose for us quite well.
Basic Tutebot chassis with analog computer piggy-backed on top.
view clearly shows the Lego Technics chassis. Soft foam rubber is useful
for protecting components. Bump switches are fabricated from
momentary-action switches. This Tutebot is an advanced model in that a
Basic Stamp is hiding under the analog computer.
For direct simplicity, LEGO building materials were used. The chassis and power train were constructed by reference to the figures in the text. The electric motors shown in the text were no longer available, but the currently offered DC motor was substituted easily. We did not use LEGO bump switches, instead substituting momentary action switches purchased from Radio Shack. The switches used had rounded plungers that could be friction-fit into the holes in the LEGO pieces used for the bumper. The resulting chassis and power train were robust, and more than adequate for the TuteBot.
The Tutebot analog computer should look just like the diagram in
text. Note the four larger relays located along the spine of the
breadboard, and the two large capacitors that are the Tutebot's memory.
Our TuteBot electronics were assembled using the parts lists published in the text. The Radio Shack part numbers found in Figure 2.14 of the text corresponded with part numbers available off the rack at the store, and so was very helpful. One of us (Caleb) has advanced LEGO building skills, and so assembled the breadboard electronics using Figure 2.15 as a guide much like following the building instructions that come with LEGO kits. This direct "visual" approach to breadboarding, while quick and efficient, does not provide learning about the way the circuit works. As a result, if an error is made, the schematic (Figure 2.13) is invaluable in the troubleshooting effort. In our opinion, errors in breadboarding are valuable in that correcting the errors will force the understanding of the circuit. We found we were only able to find errors by carefully tracing the connections following the schematic.
Once the Tutebot was up and running, our interest in understanding just what the electronics were doing was piqued. It was worthwhile to follow the authors advise to "quickly skim the circuit description and then directly put the circuit together". Seeing the robot operate, and observing its behaviors, really got us interested in understanding the details of the analog computer. The ability to change the resistance of the variable potentiometers, then directly observe the results, was exciting. We were able to elicit the wall-following behavior described in the text. The Tutebot will operate well on most floors, however we used the hardwood floor of our dining room for most tests. Carpet slows the robot and consequently draws more current from the batteries, shortening their life. The speed of our Tutebot was about 2 seconds per foot, so it was easily contained within a prescribed arena.
The construction of the chassis and powertrain are traditional LEGO , in that no particularly unique techniques were used. By this we mean that the "garden variety" LEGOmaniac will have no trouble whatsoever building the chassis. Those new to LEGO Technics may be more challenged. The castering tailwheel needed improving, which was easily accomplished by experimenting with other schemes. We found it to be necessary to fasten the bumper and bump switches securely to the chassis. Using actual LEGO switches would have made this job easier (we used momentary action switches from Radio Shack) because the LEGO switches would have mounted securely directly to the frame. We found that the DC electric LEGO motors work adequately on 6 volts even though in the various kits they are powered at 9 volts. The C-cell batteries called for in the text are quite heavy, so after a while we changed to a AA-cell pack, which seemed to have adequate capacity. The analog computer worked exactly as described in the text. It made for an excellent tutorial in analog electronics. The description in the text of the workings of the circuit required some careful study, but were thorough and understandable. (I have the benefit of a degree in mechanical engineering, which included the rudiments of DC electronics. I knew before-hand what a time-constant was, what the exponential decay of a capacitor looked like, that a diode allows one-way current, that a relay uses electromagnets to move switches, and that a transistor could be used as a switch. This knowledge did help in understanding the text quickly, however lacking that prior knowledge would only require more time to understand the description. That is, the tutorial in the text is complete and will teach you the basics needed to understand the Tutebots computer without need of extensive prerequisites.)
Involvement in a robotics group such as the Seattle Robotics Society is invaluable when embarking on a learning experience such as this. (www.seattlerobotics.org) The World-Wide-Web is populated with many robot clubs and societies. We encourage you to use one of the search engines such as Yahoo to find a group you can join. The group will be a tremendous resource for your construction and design efforts, and then as you gain knowledge and experience you will be able to contribute to those that follow you.
Our experience with the Tutebot has been very successful. The robot constructed from the instructions in the text was robust and educational. We have continued on in our studies of robots, and are building a more advanced machine to learn more about sensor technologies. To this end, the authors of the text have accomplished their intention with us.