Homemade Robots polymax improvements

Posted on Feb 6, 2014

The 2009 Robot Rally spotlighted all the flaws that result from a quick 3 week engineering and building project. Time saving shortcuts in code and hardware bit my butt several times. Failed edge detectors - Ouch! Failed beacon tracker. chomp! Ow! Line follower reversal - Arrrg! I`m happy to report I`ve investigated all the issues that cropped up

Homemade Robots polymax improvements
Click here to download the full size of the above Circuit.

and fixed them all. The bot still isn`t perfect but it`s a whole lot better than before. I`ve also cleaned up the software code and documented it better. Here`s what has been changed and fixed. Source code and schematics may be downloaded from links at the bottom of this page. The Atmel AVR ATMEGA8535P was full. I used all 8192 bytes of program space. There was no room left for enhancements or bug fixes. So, I ordered some ATMEGA644P chips from DigiKey. Only Five bucks each, such a deal! These are hardware pin compatible with the old 8535 so no hardware changes were needed. They have 64K program memory and 4k RAM. This is 8 times the memory of the old CPU. They are mostly software compatible too. Yeah, "mostly". That means spending a lot of time going over the code and finding the differences in the names and bit functions of all the internal configuration registers. Also, the avr-gcc open source compiler and avrdude program downloader I had didn`t support the 644 so I had to hunt down the latest version for the Mac. I downloaded and installed AVR Crosspack. Several days were spent hunting down bugs caused by the CPU upgrade. L293D h-bridge chips suck. They have nearly 2 volts of drop across them and run hot as hell. I was using two in parallel for each motor and they still ran very hot. Due the voltage drop the motors only got 10 volts out of 12 that was available. This means that top speed is reduced by about 20%. So, I...

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