Robot Anatomy Class

Original seed text by Gareth Branwyn

Robots are usually complex machines, but they don't have to be. They can also be quite simple. BEAM robotics, largely built from analog electronic components (resistors, capacitors, transistors, analog integrated circuits), have proven that even a simple robo-critter with no computational brains can successfully navigate a space, climb over obstacles, digest the sun (through solar cells) for autonomous power, etc.

Since learning about robots can be very intimidating, in teaching robotics, I've found it helpful for beginners to think about robotic analogies to the human body and its various anatomical systems. For my robot book, the Absolute Beginner's Guide to Building Robots, MAKE Editor-in-Chief Mark Frauenfelder (who's also an amazing artist and illustrator) did the following whimsical robot anatomy chart. While it's not to be taken seriously as diagramatic of any real robot anatomy, it gets the point across that, regardless of what type of bot you're dealing with, the subsystems are usually the same and they roughly map onto analogous systems of the human body. In designing your robot, you'll want to keep all of these aspects in mind.

1. The Frame (or Chassis) -- This is the basic structure of your robot.

2. Power System -- Most robots use batteries, usually dry cell or sealed lead-acid batteries. A lot of small robots have two battery systems, one to drive the motors and one to power the logic (the microcontroller). Some bot use stored solar power.

3. Actuators -- The servomotors, linear actuators, and other machinery on a bot that allow it to do useful work.

4. Drivetrain -- The gears, wheels, axle, and other parts that make your robot move. You'll likely be either using servomotors (hacked for continuous rotation) or simple DC motors (direct-drive to the wheels, with no geartrain).

5. Controllers -- The brains of the operation. Even a "brainless" analog BEAMbot uses the oscillating (back and forth) signal of analog chips and the other components for timing the oscillations to create, say, a back and forth walking gate in a robo-critter. Most robots have a microcontroller (MCU) or other type of main computer brain and another sub-controller, called a called a motor controller (or motor driver), dedicated to handling the drive motors' speed and direction.

6. Sensors -- How a robot interacts with its world. Sensors can be everything from mechanical switches that detect physical contact with an object to infrared, sound, light, and heat sensors.

7. Manipulators -- Some robots, like factory bots, bomb disposal robots, and humanoids, like Honda's ASIMO, have arms with end-effectors for picking up objects or performing various tasks.

8. Communication -- Many types of robots communicate with the world around them in some way, either wirelessly, or via a tether through which they can have programs loaded into them, offload data through, etc. Your bot will likely use a USB-based programming cable to connect it to your PC for transferring programs you write onto your robot's microcontroller(s).

9. Outer Shell/Casing -- Some robots protect their sensitive parts with an outer casing.

So, let's say you're building a CoasterBot. It is likely to be mainly comprised of:

1. A chassis made of CDs (along with whatever hardware, project stand-offs, etc. you care to use).

2. A two-part power system, with a dry cell battery pack for your motor power, and a separate (power-regulated) 9V battery supply for your microcontroller.

3 and 4. A drivetrain that includes (likely) two motors, wheels, and maybe gearing (especially if you end up using "hacked" servomotors).

5. Your controllers will likely be a MCU brain and a separate motor controller board. Some MCU modules have a motor control circuit built into them.

6. You'll need at least one sensor system on your bot, something that will allow it to avoid obstacles. The mechanical switch (to create bumpers, feelers, whiskers) is the easiest, most common way of creating a "first-order" level of sensor behavior -- a program routine can easily be written to detect a trigger of the switch and initiate some sort of evasive maneuver (eg. a back-up and turn). But one could also use, for instance, sound- or light-sensing to measure distance and avoid obstacles.

7. N/A

8. Your robot will likely communicate with your PC via a special USB-based programming cable that connects to a row of pins (called "header pins") on your MCU. You'll use that cable to transfer programs you've written (or downloaded from the web) onto your MCU.

As a little exercise, with the above in mind, look at Kurt Meredith's Jameco CoasterBot kit unboxing video and see if you can ascribe each component he details into one of the nine subsystems outline above.