Servo - May 2009

( www.phidgets.com) which manufactures a sizeable number of USB connected low-level device and sensor interface products. I’ll have lots more information on their products later on in this article, but don’t skip ahead just yet! Check out the ads here in the magazine for more suppliers of “ready to use” controllers.

Should you decide you’d like to roll your own low-level hardware controllers, the two most popular microcontrollers to use to handle this are the Microchip PIC and Atmel AVR. Both of these manufacturers have an enormous following and a huge amount of information on the web that is available free via Google. Both of these microcontrollers are very capable and very inexpensive hardware. Where the rubber meets the road is the assemblers, compilers, and programmers for each of them. In both cases, you can get the manufacturer’s IDE for free from their websites. For the PIC, you will want MPLAB, which is available at www.microchip.com. For the Atmel AVR, you will want AVR Studio, which is available at www.atmel.com. In both cases, you get a development environment, an assembler, and programmer software.

To use these microcontrollers, you will need to be able to program them with special hardware. Both manufacturers provide programmer hardware directly, and both manufacturers have third-party developers that provide programmer hardware as well, typically for less money. If you want to program in a higher-level language than Assembly, both the PIC and the AVR have a good selection of third-party suppliers of C, C++, and Basic compilers. The price range of these tools runs the gamut of cost from free (in the case of avr-gcc for the AVR) to expensive (for the professional development packages.) The AVR has a slight advantage in that its programmer hardware is usually cheaper and the Open Source avr-gcc project has a very good gcc based compiler that runs on any OS platform. The Microchip and Atmel supplied development environments only run on Windows, but there are some third-party compilers for each that are OS agnostic.

I’m only touching on this subject; I could write a whole article on the wealth of tool chains for both of these microcontrollers! I use a variety of tools for both of them extensively and both have very high quality capabilities and support. By way of suggestion, I would recommend that you use the PIC 24F/24H or 18F parts and the ATMEGA series of parts for your projects; don’t bother with the lesser capable devices. With both products, the prices are typically in the $3 to $7 range in quantity one purchases. If you were going to manufacture a gazillion widgets, my advice would be different, but you are doing hobbyist projects so individual part costs are not going to be on your radar; you don’t need to save ten cents on each piece.

I have two big warnings for those who are used to programming big iron machines:

1) An embedded program cannot throw an exception and

recover; the compiler won’t usually tell you when you are running out of stack/heap space, and these devices are Harvard — not Von Neumann machines — which means that the DATA and PROGRAM address busses are distinct. This will change how you think about storing and using data.

2) Because the program and data storage on these devices is small (usually less than 64K and 8K, respectively), you need to think small, efficient, and paranoid when you write a program. Timing is most important and typically you are interested in maximizing response time, not throughput. Program accordingly.

Robot Construction

To me, there are two directions that a robotics engineer can design to: the robot as an autonomous agent “in the wild” and the robot as a semi-autonomous helper. Your project leans to the latter category I think. With your project in mind, I suggest that you look into a couple of companies that have parts or kits that may come close to meeting your robot arm needs. Of course, these kits may be thought of as starter kits since they most likely won’t completely meet your needs, but they will help you get your feet wet. These companies have either good building blocks for a robot arm or actual robot arm kits. There are more out there, of course, but these are the ones that I felt might have hardware that you in particular would be interested in:

• www.lynxmotion.com has robot arm kits and servo erector set parts that you can use to build your own robot arm using R/C hobby servos. Lynxmotion also sells serial servo controllers that you can use to control those robot arms through your serial port. They have quite a variety of kits; even quite a few robot arm kits.

• www.robotis.com has the Bioloid kits that use sophisticated servos that can give feedback to their controllers. They sell from their site but they also have other distributors.

• www.crustcrawler.com sells Bioloid kits and has their own robot arm kit that uses the Bioloid servos. CrustCrawler has several kits, parts, and individual servos that they sell, as well as the ability to control them from your computer.

Robot Source Materials

I have read a few books on embedded programming and not found any that were particularly useful in a general sort of way. The topic is just too huge. However, when it comes to robot construction there are introductory tomes that I feel can give you a good grounding in construction, programming, and even, jargon. A linguist might say that these books will help you to develop a “common universe of discourse” with the