Friday, April 13, 2007

The pricewars begin...

Ok, now I understand how all those ebay-ers can sell NXT's for a "buy it now!" price of $220 and make money...

Not only is CompUSA selling the NXT for $199, but now Best Buy is doing it for $189 + $6 shipping. (thanks NXT Step!)


Those wild thoughts of buying a second and third set are getting correspondingly more tempting... =^)

Wednesday, April 11, 2007

Trackin fool

Refactoring to allow for testing is sooooo a good thing.

I finally had the brainstorm. I'd been developing two separate projects for this. One is down-n-dirty, get 'er in. Test it out. Oops..that's ugly but it works.

And one "nice, pristine, how it's supposed-to-be".

I'll let you guess which one actually made progress. For a while.

The pretty one was essentially used as a testing ground for nunit. And therefore has a nice bunch of unit tests.

And then it happened in the "real" project. Ka-blam. Hit a wall. Why isn't this working?!! It should work. The logic is right. Those d!$#m gremlins are getting in between the parsing and compiling stages. I just know it.

Deep breath. Back off. Put the mouse down. Take a walk.

Then it hits me. I'm having so much trouble (partially) because I'm having to do so much crufty liberal insertion of system.diagnostic.debug.writeline.

(true confessions, here)

And it's a PITA to debug. Because...well...things are so tightly coupled I'm not quite sure WHERE to put in the debug statements and even when I do I'm making assumptions about other pieces working and that leads to...

Well, we all know what happens when you assume.

So in a fit of brilliantly obvious inspiration, I did two things.

1.) I ported the unit tests over to the "really/working but somewhat crufty" implementation.

2.) Did some decoupling. Specifically there were two pieces:
  • determine which way way I'm supposed to go based on where I am and the target is
  • issue a command to move the robot ( myrobot.moveright() )
  • translate the moveright into actual motor directions (move motor b @ 70% power in the left direction)

The third had already been isolated. But I was doing 1 and 2 in the same function. I pulled them apart. Now a parent function says "where should we go?" and the fxn returns a "left, down" or somesuch.

NOW we're cookin. Unit tests were written for each of 4 quadrants, like so:

// $ = target point (where to move to)
// --------------------* < -100,100 (max rot values)
// | quad 1  |  quad 2 |
// |         |         |
// |         |         |
// ----------$----------
// | quad 3  | quad 4  |
// |         |         |
// |         |         |
// *--------------------
// ^(100,-75) min rot values

And as the french say, "voilia!" (literally, "let us eat cheese!")

In the end all was happy. Except tracking was much less precise than I'd like. Gear slop and imprecision in initial calibration were affecting things far more than I'd like.

So...where are we at?

The laser tracking worked best for precision...but it suffered from light refractions and went somewhat nuts in anything but a nice, lowlight environment. Oh, and if the beam was scattered or at an angle (think: shining a laser pointer on a table at a steep angle), things went wonky. Chasing butterflies.

Dead reckoning isn't particularly precise...but it's kinda/sorta "in the neighborhood".

Can I combine the two? Maybe limit the search radius for the laser pointer to within x pixels of the estimated dead reckoning solution? It's a thought.

But regardless, it'll be integrated and tested. =^)

In Mechanical news...

The gearing has been reduced and reworked for both pan and tilt. Of course, this adds to the gearlash problem, but it was necessary for precision reasons.

("Slow 'er down!" everyone said.)

(Well, not everyone.)

(Ok, maybe just me.)


But it's working. Back to "das blinkinlights" working.

But now we've got
  • boundary checking (no more chasing butterflies and grinding gears)
  • Four shot rotary magazine
  • Smaller tilt cradle footprint (geez. I should be in marketing., actually. I shouldn't)
  • A cool "fah-WOOSH!" sound when the missile is fired. (put that in for the kids)
Now it's time to put in code to track values returned from the sonar (ultrasonic) sensor. Fire when the target is within...oh...let's say 50cm.

Ok. Go to it.

Wednesday, April 04, 2007

Avast ye skirvy dogs, protect the staplers at all costs! know...that's about the highest aspiration I have for this once it's done.

Oh, and it'll look cool. And I'll have the undying admiration of my coworkers. Some of them. A few. Ok, at least one.

In other news, a reader (from whence he came I know not..!) pointed me to a project he's working on.

Check it out! Similar to JP Brown's Aegis, but with his own unique execution...and he's got pictures...LOTS of pictures, and even a few videos.

Actually, check the site out even if you're not interested in this. This guy rivals Philo for the pure amount-of-stuff that he's built and documented. I particularly liked the automated battery tester.

In general construction news...

Given my own...umm...unique execution of the pan-n-tilt, I may have to crib some of these guys' executions. If nothing else, I'm thinking of rebuilding the firing mechanism with a conventional lego motor for compactness.

Of course, then I lose the ability to control rotation via the built in rotation sensors...drat drat drat...everything's a tradeoff. Hmm. Maybe I'll just attempt to rebuild using the nxt motor and trying to move things more inboard...

In other news, the dead reckoning method for moving stuff around is's coming...umm...yeah.

After more than a bit of headscratching the boundary detection is working. That is, I can calibrate the "aim box" for the beast (max and min horizontal and vertical rotations) and if we start to point outside of those boundaries, the control code catches it and moves back inside.

However, I had two setbacks when translating this to dead reckoning movement.

1.) I've got a @#$!$ bug in the code. Currently whenever I tell it to "track to a point!" it's thinking that the point is somewhere between it's toes and left armpit. Ie, it moves left and down...left and down...always left and down. I've stared at the code till my eyes bugged out and the logic error is still eluding me. But I'll find and squash it. (eventually)

2.) I..umm...err. (this is really embarrassing) I lost my control buttons. Yeah, these:

I was playing with tab layout controls, and I think somewhere I grabbed and moved them. Somewhere. As a group.

And now while Visual Studio thinks they're there (and all the handlers/etc are still present) they are naught to be found on the form.

Of course my (ever bright, savvy, and non-developer) wife's perspective was: "You have backups, right? You keep versions don't you?"

Argh! All that ranting and raving about idiots who code without source control comes crashing down upon my head...she must have actually been listening.

Yes, I do have a previous version in subversion. And it's only about 2-3 days old. But there's still quite a bit of difference 'tween the two.

The painful lessons are the ones best learned. (and this could have been MUCH more painful!)


Tuesday, April 03, 2007

Mindstorms NXT $199 @ CompUSA!

I just happened to be at my local CompUSA about 2 weeks ago looking for (oh the irony!) an inexpensive USB joystick to control the robot.

Low and the same aisle, facing shelves on the bottom were [da dum!] Mindstorms NXT kits. "Nifty enough", says I, "but what's that little sticker..."

Holy hot hannah batman...$199! (the sticker said "new low price!")

The link above is to the online store, which also reflects the $199 price. Alas, they are all sold out for delivery. However, my (local) store has some in...if you have local CompUSA you might just be as lucky!

I've been itching for a second set already...mostly because I keep getting inspired by other folks' creations and want to give 'em a try without tearing apart my work-in-progress. Oh the agony, your name is Lego...

And the joystick? Eh...didn't buy one...yet. I'll tackle DirectInput and the attendant control issues later.