I usually save the interesting dev kits for a holiday when I have a chance to really play with them. This is why I was looking forward to checking out Digilent's latest kit from its Mechatronics collection. The Digilent Robotics Kit (Fig. 1) comes in a number of variants including a remote control version and a line following version.
The kits utilize Digilent's Cerebot 32MX4 (see Low-Cost Kits Make Evaluation Faster). All the components are available separately like the Motor/Gearbox with encoder (Fig. 2). The robot uses a pair of these plus a stub to provide balance. This tripod approach to robots is quite common and works for lightweight machines like this. It is possible to add another pair of wheels since both the motherboard and frame can accomodate the addition. Most other robot kits would not be as amenable to such changes. On the other hand, a four wheeled vehicle is more difficult to move accurately.
The key to expansion is the fleibility of the Cerebot 32MX4 using Pmods (Fig. 3). In this case, the H-bridge PMod has inputs for the encoders on the motor/gearbox drive. This Pmod plugs into the motherboard for control and accepts a power cable to drive the motors.
The PMods can plug directly into the motherboard or they can be located farther away using a Cerebot extension cable (Fig. 4). There are wide range of Pmods (Fig. 5) available from Digilent. These include everything from SD card interfaces to an SPI-based Ethernet adapter. Many are handy for robotics work like the tiny joystick Pmod (Fig. 6). The biggest problem I have with the Pmods is most do not have a mounting hole. This is not an issue for the robot where they are often moved but a more rugged mounting would be handy for other embedded projects.
The Cerebot 32MX4 is a nice platform for robots with plenty of expansion and support for servos. It works equally well for a wide range of embedded applications. The board contains an 80 MHz Microchip PIC32MX460F512L based on MIPS 32-bit architecture. It has 512 Kbytes of flash and 32 Kbytes of RAM. On the analog side is a 16 channel, 10-bit, 500 K sample/s A/D converter. The fve 16-bit timers have 5 input capture ports and 5 PWM outputs. The board exposes the following ports.
- 8 - 12-pin Pmod headers
- 1 - 6-pin Pmod header
- 8 - R/C servo connectors
- 1 - USB port
- 2 - SPI ports
- 2 - I2C ports
The board can be powered from the USB connection. The robotics kit includes a battery pack for self sustained operation. It also comes with an LCD display and interface Pmods.
Assembling the Robot
The kit includes the usual batch of brackets, motors, bolts and circuit boards. The motors and wheels are small but they rugged and accurate. I like Digilent's design compared to the Texas Instrument's Evalbot (see Transforming Circuit Board Into Robot) based on the latest 32-bit Stellaris Cortex-M3 microcontroller. Digitlent's approach is modular and expandable.
Assembling the robot is a matter of following the directions and bolting and wiring everything together. The design follows the typical small robot layout with the batteries and motors underneath and the circuit boards on top. Things get more interesting once everything it hooked up.
The documentation provides an introduction to the hardware and the software that includes Microchip's MPLAB IDE and 32-bit C compiler. MPLAB works with any of Microchip's platforms and provides excellent support for Diligent's robot. The IDE interfaces to the Cerebot board via a USB cable. Sample applications are provided and highlight the Pmod interface and the peripherals. Motor control is part of the mix.
What is missing from most of the kits are sensors like Parallax's PING))). The line following kit does use the infrared detector module. Luckily interfacing is easy using the Pmod interface and the peripheral support of the PIC32.
The Remote Control Kit version of the robot includes the joystick Pmod. This is connected to the robot by a long cable so the Pmod is essentially part of the robot. Wireless solutions are available but this particular implementation lets you follow the robot around and provides simple but immediate feedback.
The big issue comes once you have made it through all the tutorials. At this point you have a solid platform and a C compiler. This is one reason why the platform has done will in colleges where additional expertise is available. I like the kit's possiblities. The microcontroller is powerful and has lots of program space. Definitely check out Digilent's platform if you are looking for a more advanced robotics platform in a compact package.