Monday, February 28, 2011

AVC Bot: Frustration

Sometimes things just go to crap.

Here's a position plot from a recent test run up and down my street. I'm pretty sure the robot didn't travel through houses to a cul-de-sac two blocks east.

Since I need precision that's considerably tighter than a city block... if you can tell me how to use this garbage to reliably navigate to 10' precision I'll kiss you. (Not really, that would be weird).

GPS: I'm screwed.
The GPS is supposed to be really sensitive and high performance (hmph). Horizontal Dilution of Precision is a pseudo measurement of GPS fix quality and 1.0 is excellent, with larger numbers indicating decreasing accuracy. Here's my plot:

GPS: Yup, I'm screwed.

So, basically my GPS fix bites.

The irony here is that my cheapie, piece of crap Garmin eTrex Legend taped to the RC chassis with electrical tape was reliably performing far, far better than this high-zoot, fancy-pants GPS. What's up with that?!

On to other sensors. Here's my plot of Gyro, Compass, and GPS headings, fraught with problems.

Heading data: Yup, screwed
The GPS fix data is lagging reality by about 1 second. Meanwhile, compass readings are haywire as soon as the initial turn starts.

Of course those are minor issues next to the fact that error between the three sensors are on the order of 100 degrees. I need 1 degree precision. Only 2 orders of magnitude. I'm in great shape, aren't I?!

Ok, I did stack the compass module on the GPS module with double stick tape for convenience so that probably hurt the performance of both units.

I decided to move them... and the shield ripped off the GPS! (*&!@#!

I had to resolder the shield. I hope it works or I'm out a $60 GPS module. For that matter, I hope it works better than before. EDIT: nope, it's trashed. Doesn't even power up properly. *sigh*

I guess I can still try the 1Hz, 4800 bps, iGPS 500 and hope it can get a better fix.

On top of the problems with sensor data being wildly inaccurate I can't even troubleshoot properly because I can't get the bot to reliably log data to the microSD card. I end up missing huge chunks of time.

I spent 5 minutes driving the truck around and I looked at the logs and find 60 seconds of data.

Uh... ok. Thanks.

Piece of crap.

Oh, and last week, I bashed the RC truck into a parked van (good thing the Robot will do all the driving), broke the front body post mount and dented the crap out of my FPV camera.

And I still don't have the Kalman filter going. Mostly because I don't have useful data to work with.

Time for serious measures. Time to bring in the magic rubber chicken!

So in summary, things are just freakin' peachy.

Are we having fun yet?  Ok, driving it is fun...


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