View unanswered posts | View active topics It is currently Wed Dec 17, 2014 7:07 pm






Reply to topic  [ 5 posts ] 
dGPS; Just a few questions. 
Author Message
Senior Roboticist
User avatar

Joined: Wed Sep 28, 2011 10:13 pm
Posts: 630
Location: If I told you, I'd have to kill you.
Post dGPS; Just a few questions.
I recently acquired the Dexter Industries dGPS sensor to be used in a robot designed to compete in the SRS RoboMagellan contest. I have a few questions about it.

1. How fast can it be polled? I see in Xander's sample it polls the data ever 0.5 seconds. Can it go any faster? Is it know, or do I just have to try?
2. How accurate is it? Comparable to a phone, say? I'm not sure if I'll need to incorporate encoder data to supplement the GPS data for position.
3. Once it gets a workable signal, how apt is it to lose it? I've been trying it in a pretty enclosed area, but it seems to work fairly well.

_________________
A.K.A. inxt-generation
Self-proclaimed genius, and future world dominator.
My Brickshelf Folder
"Don't they teach recreational mathematics anymore?" - The Tenth Doctor
Bow down to Nikola Tesla, King of the Geek Gods.


Thu Jul 18, 2013 3:51 pm
Profile WWW
Expert

Joined: Thu Sep 29, 2011 11:09 pm
Posts: 184
Location: Michigan USA
Post Re: dGPS; Just a few questions.
No solid answers here, just some related rule-of-thumb information.

In general, GPS modules are accurate to within about 5 meters (unless they are a DGPS, which is something totally different from a dGPS). Typically a GPS will update 1, 5, or 10 times a second.

I have no idea what the specs are, for the GPS on the dGPS, and I don't know how often the dGPS FW allows for updates. I'm guessing that it's probably accurate to within about 3 to 5 meters. Whether or not you need to use encoder data as well will depend on the setup/project/contest.

_________________
Matt


Thu Jul 18, 2013 4:46 pm
Profile WWW
Professor
User avatar

Joined: Sat May 18, 2013 1:24 pm
Posts: 272
Location: Olympia, WA
Post Re: dGPS; Just a few questions.
Once a GPS module locks, it should be able to keep that lock, because it will know which satellites it's communicating with and where the other ones are.
According to the dGPS wiki (http://dexterindustries.com/manual/dgps-2/), you can get an accuracy of 3 meters. But since it's just a commercial module, it is really only guaranteed a 5-meter accuracy. When people talk about higher accuracies, they're usually talking about a GPS with augmented accuracy (WAAS, DGPS <-that one really confused me!). DGPS=differential GPS, not Dexter. Apparently you can get 10cm accuracy with that? But RoboMagellan doesn't seem to allow DGPS.

_________________
FTC Team 6424, the 'Oly Cow - Chief programmer.
FRC Team 4450, Olympia Robotics Federation (ORF).

and also quadrotors. Quadrotors!


Fri Jul 19, 2013 12:17 am
Profile
Senior Roboticist
User avatar

Joined: Wed Sep 28, 2011 10:13 pm
Posts: 630
Location: If I told you, I'd have to kill you.
Post Re: dGPS; Just a few questions.
It seems I *can* cut the polling down to 1/4th of a second, but it doesn't seem to be updating much faster anyway. I do live in a pretty enclosed space however, so in the field it should perform better.

The accuracy should be good enough for my specs. And yeah, dGPS and DGPS, big difference! :lol: It sure confused Google.

I did some tests today. The GPS seems to be working reasonably well. It's just MY code that was failing. :oops: I need to try something new... it seemed to be actively trying to avoid the waypoints... :?

And did I mention, this needs to be semi-working by August 3rd :P

I must be tired. I never use this many smilies...

_________________
A.K.A. inxt-generation
Self-proclaimed genius, and future world dominator.
My Brickshelf Folder
"Don't they teach recreational mathematics anymore?" - The Tenth Doctor
Bow down to Nikola Tesla, King of the Geek Gods.


Fri Jul 19, 2013 12:28 am
Profile WWW
Moderator
Moderator
User avatar

Joined: Wed Mar 05, 2008 8:14 am
Posts: 3297
Location: Rotterdam, The Netherlands
Post Re: dGPS; Just a few questions.
The GPS has a max frequency of 4Hz, that's the spec. It can go to 1Hz as well, I believe, but it's been a while since I last looked at the actual specs of the chip.

= Xander

_________________
| Professional Conduit of Reasonableness
| (Title bestowed upon on the 8th day of November, 2013)
| My Blog: I'd Rather Be Building Robots
| ROBOTC 3rd Party Driver Suite: [Project Page]


Fri Jul 19, 2013 2:05 am
Profile WWW
Display posts from previous:  Sort by  
Reply to topic   [ 5 posts ] 

Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  



Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group.
Designed by ST Software for PTF.