One of the key components of any robot is the onboard
microcontroller or MCU (Micro Controller Unit). The microcontroller
typically interfaces directly with the robot’s sensors (e.g. sonar
and infrared), some number of servos (e.g. for controlling an arm), and
ideally provides a means for controlling at least two drive motors
and reading encoders.
Arguably the best known microcontroller among hobby robot builders is the Arduino.
The Arduino’s hardware design is open source so that a number of
clones are available which offer a variety of features for supporting
different numbers of sensors, motor controllers, and communications
protocols (e.g. XBee).
Basic ROS support for the Arduino exists in the form of the rosserial
stack. However, rosserial does not include support for controlling a
differential drive robot with encoders. (One of the authors of
rosserial explained that the primary goal of the project was to provide
support for reading inexpensive sensors and controlling servos but not
to control an entire robot.)
To fill this gap, I used some of the Winter break to program a new ROS stack for the Arduino, called the ROS Arduino Bridge. With the help of feedback from a number of members of our local robotics club (HBRC),
the new stack seems to work well on a number of different hardware
setups. In particular, Pi Robot has swapped out his Element and ArbotiX
controllers for an Arduino Mega 2560 R3 together with a Pololu motor controller and a Robogaia Encoder shield. This hardware and the new code are stable enough to run the ROS Navigation stack and indeed, Pi passed the navigation endurance test with flying colors using
his new hardware.
The same exact hardware is now being used on Pi’s newest cousin, called
Scout, who was built over the holidays to test the new code. More about
Scout in a later post.
The good news for both Pi and other robot builders, is that the ROS
Arduino Bridge software provides an open source solution for robots
running the open hardware Arduino platform–a combination that should
provide some stability and a variety of choices well into the future.