Introduction to Robotics project:
Assembling and Programming Talrik II robot.
· Sensors
· Sensors
Appendix B: List of Images and Movie Files
The Talrik II
robot kit offers an expandable, programmable, autonomous, mobile robot that
fits into a circular cylinder of 10-inch diameter & 10-inch height. Talrik II TM is constructed 5-ply model aircraft birch
plywood, and strong black ABS Plastic & rides on two 3-inch Du-Bro wheels
& a rear caster. Two high quality
ball bearing R/C servos, modified as gearhead motors and mounted underneath the
platform, drive each wheel. The robot
contains the suite of sensors and 64Kb memory chips that can be programmed
using the tools provided by the vendor. After assembly, the robot can be
programmed in the development environment C, and all the libraries can be
downloaded from Mekatronix (the manufacturer) site. Some testing and sample C programs are also provided. Here is the picture of the complete robot.
· Talrik II TM Controller System (The Brains)
Talrik IITM features the MekatronixTM brand MRC11 robot controller which has a MC68HC11 brain & 64 Kbytes of memory. Talrik IITM also includes the MekatronixTM brand robot sensor expansion board, MRSX01. This board interfaces with the MRC11 through a 60-wire ribbon cable & conveniently stacks on top of the MRC11. The MRSX01 provides convenient, user-friendly interfaces to all of the Talrik IITM sensors & servos. The MRSX01 board has recharging circuitry with diode protection, a charge-light LED indicator, & a power-on LED indicator.
The sensors of the TalrikII TM include 12 IR emitters that illuminate the Talrik IITM environment with invisible infrared light. The emitters are complemented by 12 IR detectors that allow the user to control the robot programmatically. Also the sensors include 10 bump switches, 6 CdS photoresistors, battery voltage level detectors, and recharge current detectors.
The bumper detects individual switch closures, allowing Talrik IITM to determine multiple, and simultaneous collision points & ascertain where the collision(s) occurred on the circular plate to within about 15 degrees.
The kit includes two servo gearheads, one pan head servo, two lightweight low bounce wheels, one rear caster, one polycarbonite bumper ring and a Viking helmet bumper. The bumper is an optional element that protects the bump switches in the event of a collision. The Talrik IITM Bridge has five slots cut to enable mounting up to five standard size servos (such as the MS492) and holes drilled to mount two stand-alone single chip microcontrollers (such as the MSCC11E2). In the second photo, a sensor head configured, with three photoresistor light detectors, mounts on a high quality servo inserted into the central slot on the bridge. This Pan-Sensor-Head, a standard feature of the Talrik IITM Robot Kit, permits us to write programs that enable Talrik IITM to track light beacons and characterize ambient light conditions while scanning through slightly more than 180 degrees. In the future, the manufacturer of the robot will offer a variety of different pan sensor heads. These ADD-Ons will provide the opportunity to extend the aptitude of the robot’s functional behavior.
Talrik IITM is recharged via a 12 volt DC panel jack on its left bridge support. The control switches for the Talrik IITM mount directly on the right bridge support for easy access.
The purpose of this report is not to fully describe the assembly sequence, but rather just to mention the highlights and the most interesting points. For additional information on the assembly process, please refer to the complete assembly manual at www.mrrobot.com. I followed the assembly manual precisely and found it most helpful, especially in pinpointing the challenging areas of the assembly process. However, there were a few discrepancies in the procedural instructions, for example, the circuit boards did not exactly match the specifications mentioned in the manual; and more pictures would have made it easier to assemble the body of the robot. Nonetheless, the instructions were coherent and provided a straightforward schema to follow.
I started with cutting all the body parts out the pre-cut ply wood list. The body was assembled using fast-drying carpenter glue. Then, I added the bridge that holds the sensor head and the motor that spins the three photoresistors.
The next step was to mount the wheels on the hacked motors. The wheel horns were very difficult to center with the screws provided in the kit and I ended up gluing the horns to the wheels with superglue.
Before hacking the servos, I had to solder the circuit boards and then attempt to install them on the body of the robot. The servos are supposed to be inserted into the servo mounts, but, for some reason, the holes in to the mounts were not big enough for the servos. Some simple carving solved that problem. On the same step, I hacked the IR sensors (see below) and installed them on the body at approximately 15 degrees apart. Then I glued the front and back bumper switches on.
After hacking the sensors and the motors (see below), I did the final assembly and wiring. Wiring turned out to be the longest procedure, as the Talrik has an abundance of sensors!
The robot kit includes digital IR Sensors that must be converted to analog IR sensors. This requires some modification in the sensor. I carefully disassembled each sensor and rewired it according to the manual. The operation was fairly simple, but nonetheless, I accidentally broke off a piece of the first sensor that I had tried to hack.
Programs execute on the Talrik II motors using pulse-width-modulation (PWM). For the PWM program to work one must first hack the servos into DC gearhead motors. This operation requires disassembling the servo and using potentiometer and Hservo.S19 program (provided by Mekatronix) to center the potentiometer settings. According to the manual this operation almost ruins the servo but allows you to have a DC gearhead motor with electronic control.
Fortunately, the manufacturer provides the user with primitive interrupt routines upon which we can develop simple programs or behaviors. Moreover, according to the manufacturer, changing the drivers is strongly discouraged. I began by downloading simple testing programs in order to investigate the response of the sensors and motors. The further development requires using Interactive C which is supplied by the vendor. Interactive C is basically a command line environment that consists of a PCODE interpreter that must be downloaded into the robot’s memory. The interpreter then translates byte-code instruction generated by Interactive C. Therefore, Interactive C compiles your programs specifically to this kind of byte code. PCODE virtual machine interprets highly encoded C language statements directly (doesn’t it remind you Java?). Interactive C also comes with DOS freeware that runs on Windows 95. Interactive C is not a standard C; however, it is similar enough, according to my personal experience. For more information, please, refer to www.mekatronix.com.
Talrik II programs provide the basic hardware interrupt and device driver routines for the robot. These allows the user to access the sensor readings and control the behavior of the motors and servos. Potentially, the user can program an unlimited number of behaviors. Some sample behaviors are mentioned in User’s Manual of the Talrik II. Those include primitive behaviors like collision avoidance, light avoidance, light following, wall following, and exploration behavior. The primitive behaviors then can be combined in order to produce more sophisticated ones. For example, a more sophisticated type of behavior would include making maps and then following its own maps.
This report in MS Word format.
