Servo - July 2011

Robots: Form or Function?

www.servomagazine.com/index.php?/magazine/article/july2011_ThenNow

FIGURE 3. DLR's Rollin' Justin space robot.

FIGURE 2. NS- 5 robots from the film, “i-Robot.”

fall flat on its face. They don’t realize the complex programming involved, with inputs from accelerometers, gyros, and other sensors. We view the process of walking for humans the same way, not knowing about the ear’s semi-circular canals that act as dual-axis accelerometers and gyros.

Figure 3 shows another very functional robot — DLR’s ‘Rollin’ Justin’ from the German Aerospace Center. Justin was built as a prototype astronaut’s aide for space applications, much the same as NASA’s Robonaut II. This latest version has a wheeled base for terrestrial travels. Justin recently made the route of You Tube videos as he was seen catching one and two balls at the same time, with a catch accuracy of 89%. Afterwards, he was seen pouring himself a cup of coffee. Some people may say “big deal” to that, but I’d be willing to bet that a person making those kinds of comments could not build any of the robots mentioned in this article.

The Design Process

FIGURE 4. Jim Hill's Charlie in Popular Mechanics.

FIGURE 5. Jim Hill and Charlie.

(Photo by Roger Ressmeyer.)

Most of us do not use FEA or CAD programs in our machine’s design process. Instead, we might start with a flat piece of metal “that looks just about the right size” and we begin the design process by laying the different parts that we’ve collected on this base. For a differential-drive robot, we might place two gear motors (or servos for a small robot) centered on the sides of the base and determine how we’ll mount these motors and attach the wheels. We then might add two spring-loaded castors fore and aft.

At this point, we have a basic robot base; the addition of the rest of the components is a bit easier. The heavy battery is usually placed down low and centered for stability. The processor, H-bridges, sensors, and any appendage can be mounted on the main base or on a smaller base on top of four long spacers. As for arm designs, we can look into our pile of parts and find a large servo or gearmotor of a certain torque and speed, and ‘backward engineer’ the design process to fabricate an arm that will lift a certain weight. If we need more lifting capacity, we either shorten the arm’s length or gear down the speed to obtain more torque. (Again, the actual design process is a bit more complex than this.)