AvronicsFirstBot

AVRonics Simple Robot

Now that the AVRonics board is in full swing it's time to start stretching it's legs. This is not the robot to do that but it's a start. I threw this together in about an hour (after many months of thinking) and spent about 10 minutes writing the code to control it. No, no, I'm not just that good - it's just that simple. This robot is now used for AvronicsMicroMouse development.

money shots

purpose

the purpose is 5 fold

• 1. provide a quick and dirty platform for testing out the AVRonics board
• 2. i haven't built a robot in a long time and i needed a fix
• 3. this platform is intended as a prototype for a future cheap swarm
• 4. this platform is to be used in behavioral tests for a robot we are designing at work
• 5. everyone needs a robot running around their house

hardware

• 2 modified servos (glorified gear motors - with drivers built-in! )
• sheet metel folded into a channel
  • houses the battery/electronics
  • holds the servos together
• 2 ice tea bottle caps
  • i punched holes in these to screw them into the servo
  • 'spot welded' in place with JB Weld
• 3.6V rechargable battery from a cordless phone
• and of course the AVRonics main board

hardware that's missing

• any type of sensor!
• 5V+ battery (motors spin faster when they have more juice)
• traction - the bottle caps are slippery metal
• caster - right now it drags its arse
• communication - swarms need to communicate preferrably wirelessly

software

the built-in h-bridges are inverting so a 0 turns the motor on, 1 off... that is why 0xfc turns the motors (using pins B0 and B1) on and off. this is a really poor way to drive your robot! don't do it if you have built in pwm! don't do it even if you don't have pwm - hack some code together. this code sucks for a real robot! i think you get the point.

hflag is a variable that is incremented whenever the heartbeat thumps. The heartbeat is a system timer that normally flashes an LED to indicate that the program is still running. It is also on port b so this code keeps the led on all the time, however, the heartbeat still thumps away even though you can't see it.

/* probably the simplest program to drive this thing.
 * this code wont last for more than one or two tests
 * but will get the mouse rolling.
 */
void main(){
        DDRB = 0xff; //all outputs
        PORTB = 0xff; //inverting h-bridge
        configure_rti();
        PORTB = 0xfc;//motors on
        for(;;){
                if((hflag%6==0) || (hflag%7==0) || (hflag%8==0)){
                        PORTB = 0xfd; //right motor off
                }
                else{
                        PORTB = 0xfc;
                }
        }
}

update

ok it's only a hour later but i've updated the code to use the pwm built into the ATmega32. The power of this is really lost on this robot (the hacked h-bridges are pretty much on or off) but it was important for the avronics board that this be done. The robot now runs a program called left-right-left in which the motors fire one at a time to make a zig-zag straight line.

watch the video and you'll note that the wheels get stuck a few times. this is due to the fact that they have no traction. this will be remedied soon.

-- ChristopherPepe - 17 Mar 2006