Friday, July 11, 2008


Thinking through the navigation stuff... was thinking maybe it'd help to have steering correction that is non-linear with regard to the distance to the wall. Thankfully Grapher on the Mac makes it easy for a guy like yours truly to visualize some possibilities. I don't have it worked out and won't before tomorrow.

Rather than working out some complex equation, maybe a simple lookup table is easiest to concoct. What I'd want is minor steering correction (extremely long radius turn, so a small ratio of left to right speeds) for, let's say up to ±2cm distance, with increasingly harder (higher ratio left to right, shorter radius) turning for up to ±10cm distances. Beyond that, a routine that stops, searches for the wall angle, drives perpendicular to the wall and stops within the right range.

The other thought is, when you're driving a car and you want to change lanes, you don't just turn and hold your steering wheel. You turn it until you are starting to change direction at the rate you want, then you center the wheel, then turn in the opposite direction when you get into the correct lane. In correcting (especially large) distance to wall error, the robot should turn to correct distance errors but stop turning as it approaches a maximum rate of change in error, then turn the opposite way as the distance error grows low enough, seeking both 0 rate of change and 0 error. How would I get all this to work? I don't know for sure.

What I do now for sure is that once again I have no time to finish. Didn't this happen last time? A midterm that showed up right at the same time as the robotics contest? Hmph. So much for vindication... :)

So, will run Pokey as-is. I know he can get to the hard room with moderate consistency. I don't know if he can make it to room #2 let alone #3. #4 is right out. The candle scanning routine is no better than it was when it failed miserably last time. Ah well.

There's always next time :)

Meanwhile, the robotics expo / contest is going to be a LOT of fun with some cool vendor attendees and lots of robots to look at. Really looking forward to it!

Wednesday, July 9, 2008

Hacking Session #1

Spent a couple hours in the garage hacking on Pokey to try and improve the wall following. While it is working better, it isn't quite dialed in. Probably the right way to go is to self-calibrate to a target wall distance, hold that while wall following, and execute constant radius turns to maintain that distance within some small error range. That'll take time that I may not have...

One problem, which George M. astutely pointed out at a SHARC meeting many months ago, is that when the robot turns at too steep an angle to the wall, the angle of the sensor to the wall increases dramatically, affecting the accuracy of the distance measurement. So avoiding steep angles is helpful but difficult if the robot gets significantly off course and has short runs of wall. He did have a solution for this issue that I may explore.

As time permits today I'll noodle this over some more and see if I can come up with better solutions. I still think the wall following is key. If the robot can align to a wall and keep a set distance, navigation gets much, much more reliable.

Monday, July 7, 2008

Less than One Week!

Less than one week remains before the autonomous robot firefighting rematch on July 12! It's part of a cool robot Expo with vendors and other competitions.

Unfortunately, I've spent absolutely no time on Pokey in the last few weeks. I just got back from the hardware store with some fiberboard that I'll be turning into a full scale replica of the firefighting arena so I can get crackin' on Pokey's code over the next handful of evenings after work. Along with working on a midterm and course project, and prepping the Jeep for the big trip in two weeks.

Well, here goes, the old college try, the last minute hacking, try to pull it all together just in time. Stay tuned to see how it goes. Your guess is as good as mine!