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1、Rapid Prototyping of Small Robots Draft Grigoriy B. Reshko Carnegie Mellon University Pittsburgh, PA, USA reshkori.cmu.edu Matthew T. Mason Carnegie Mellon University Pittsburgh, PA, USA matt.masonri.cmu.edu Illah R. Nourbakhsh Carnegie Mellon University Pittsburgh, PA, USA illahri.cmu.edu 1. Introd
2、uction This paper describes our work on high quality rapid prototyping. The focus is on techniques that produce prototypes of desired quality and yet do not take long to build. We present necessary information about methods of control, power, sensors, batteries, electronics, and more. We outline mat
3、erials, methods, and tools. We also explain how to use servomotors, Lego, and electronics to achieve satisfying results. Figure 1 shows an example of the kind of project. With the right tools and materials, and with parts on hand, the omni wheel telerobot took less than half an hour from conception
4、to completion. 1.1 Why prototype? We have noticed that some designers tend to prototype very quickly 1. Sometimes you can learn something important in a few minutes from a prototype that might have taken weeks or months otherwise. Mechanical design seems to require iteration, so, the faster you can
5、iterate, especially at the beginning of a project, the better. 1.2 Levels of prototyping Prototyping ranges from an idea to a complete product. The quality and the level of detail of a prototype should depend on its purpose. For example, Figure 1 shows the first prototype of the Palm Pilot Robot 5,
6、which at this point is nothing more than three servos taped to a receiver. This simple model is sufficient to fulfill its purpose of demonstrating holonomic motion of the base. Later we built a more complex prototype with sensors to show that the robot can follow walls. 2. Control We examined and te
7、sted three types of control of prototypes: human powered prototypes, remote control, and computer control. 2.1 Human powered prototypes One of the most common goals of prototyping is to demonstrate a concept or an idea. Usually complexity of a prototype varies with the complexity of an idea. Relativ
8、ely simple or predictable prototypes do not need motors and batteries they can be powered and controlled by humans instead. An example of a human- powered prototype is a regular four-wheel LEGO vehicle in Figure 2. There is no need to attach motors and remote-control equipment to demonstrate that it
9、 can move back and forth. On the contrary, it is impossible to demonstrate wheel traction simply by turning the wheels. Therefore, prototypes in which human Figure 1 Figure 2 Rapid Prototyping of Small Robots 2 intervention affects the results require a remote or computer control system. 2.2 Remote
10、control Human remote control is useful when precise or unusual methods of control are required. It is also the simplest way to control a prototype without actually physically interfering with it. For example, the fastest way to determine what happens to a robot that rapidly accelerates and then dece
11、lerates is to use a remote control system. A simple and easy to use remote control system for model airplanes will suffice to demonstrate whether such robot will immediately come to a stop or skid for a certain distance. Such control system has four channels and provides good range, reliable communi
12、cation, and up to four proportional controls, which allow smooth adjustment of speed or angular position of servos. An example is Three-Wheel Mobipulator robot. Human remote control provides an easy method of control of the steered wheel and the brake at the same time, while not requiring any progra
13、mming or additional electronics. 2.3 Computer control When a robot requires precise and complex operations or is involved in an application that requires sensors or computer feedback to take actions, the computer control becomes the right choice. An example of such control is a simple autonomous pro
14、totype with encoders on its wheels driving in a straight path. Companies develop a variety of boards with different capabilities that can control servo and stepper motors by means of serial or parallel communication with a computer. Some boards just translate commands from a computer to PWM signals,
15、 whereas others are programmable. Pontechs SV203 board is a good example of a relatively simple and inexpensive computer control system. It uses serial communication to talk to a computer and can run by itself. However, it is very slow and simplistic compared to a desktop computer. Most boards have
16、very limited number of functions and the amount of memory. Although the board by itself can be sufficient for a number of applications, the two alternatives are to use a tether and connect a robot to a reasonably powerful computer, or to use a more complex board such as 68HC11 chip or BASIC stamp. Another advantage of computer control over the previous two methods is the ability to use sensors. Most control boards have already built-in analog and digital inputs and can connect to a
