cr2cX - The long story
December 2, 2010
cr2cX was born as a robotic platform to test and experiment various concepts of the robotics field.
Because I have designed and build a robot 16 years ago I considered that it will be useful to start again and teach my kid some things. I have taken the hard way by designing and building every module and piece of software. To be able to speed the building and experiments a little, I've taken some shortcuts:
- I have used ATmega328 with Arduino bootloader;
- I have done the programming in Arduino language;
- I have used L293D H-Bridges to skip (for now) through the adventure of designing my own.
Living in Romania I did not found too many online shops so I had limited choices. First I have brought a Tamiya Gearbox and assorted wheels but I dropped the idea of using it because of the motors (low voltage and not so low current). However, I have build a H-Bridge with a L298 but did not used it. If I will find Solarbotics replacement motors I will build a small, tank like, robot with Tamiya threads.
Next, I have found a nice shop (robofun.ro) with good prices and the journey started with ATmega328 and micro metal motors.
When I was searched for a microcontroller I have found that for me ATmega328 with Arduino bootloader is the most handy option, both as availability and price. This has made me think of Arduino. The board was designed to be somehow bare bone, Arduino compatible (to use the bootloader, language and IDE) and with headers to be easy to connect modules.
I do not really like to use standard batteries and charge Ni-based accus so I decided to search for some Lithium based accu. I have found at a good price a noname replacement accu for one of my old videocamera, hence the charger was allready available, and I brought one. Because of the difficulty to make a connection socket for that type of battery (read: I made one but I did not considered it to be good enough) I soldered wires to the battery and build a pretty dumb but usable charger.
Did not had too many choices so I have brought two 60 RPM/6V micro metal gear motors and Pololu 42x19 mm wheels. I have made some brackets, did not liked them then brought Pololu brackets.
Having the accu and the motors, the design of power module was quick ... after more then a week of thinking between using standard regulators or switching regulators. I've decided to use standard regulators for now and promise myself to use a switching regulator for the next robot.
In the idea of reusing it I have build a motor driver with 2 x L293D (one L293D per motor with the H-Bridges connected in parallel) to be able to provide safelly some "decent" ammount of current.
I really wanted to build these from scratch. I have found the L53F3BT IR LED Emitter and the L932P3BT phototransistor to have the same IR wavelength and viewing angle and brought them because it was the only combination that I had easy acces to.
After the first tests I have made 4 boards for sensors and populate 2 of them. Even if the tests were good, onto the robot the results were poor. I have changed some resistors and added a transistors as amplifier, the result was totally unusable! Did not worthed the amplifier because it was way too sensitive to ambient light so back to the first drawing.
I've added the IR parts to the other two boards, changed the resistors for IR Emitters to 68 ohms glued them like in the pictures (see the cr2rX page), a few versions of the reading and processing software and bam! good, usable, results.
It was a pain in the a$$ to setup, calibrate and write the code for good use. (see the video in the cr2rX's page).
The first chassis was made from circuit board, but for version 2 I have used a CD and some spacers.
cr2cX stands for Calin's Robot no.2 Construction version X.
cr2r2 is the current version, schematic is attached in the robot's page.