Comments

• Derek February 11, 2013 at 9:09pm

  A cheaper option may be set out a marked number of waypoints on your own test course and beg,borrow or steal an accurate D-GPS to mark your start and waypoints. Whatever your own setup for GPS, heading and hardware you can then test and tweak against accurate readings  You may find that actually although your setup isn't accurate it could??? have constant offsets.

  I know that some systems that are used to monitor players on sports pitches measuring performance, speed, distance run etc. use this principle when each player carries his own GPS. 
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  KM6VV February 11, 2013 at 8:52pm

  I looked into DGPS a long time ago, it required a receiver and a license with a monthly bill.

  Two GPS receivers are used on large freight ships or tankers, to assist in leveling and trimming.

  I don't think they'd be of use to us.

  Alan  KM6VV

  Alan KM6VV
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  Anthony White February 11, 2013 at 8:35pm

  Differential GPS (D-GPS) is an interesting option from the hobbyist level - while certainly theoretically possible, a lot interdisciplinary problems would need to be solved - primarily coding some fancy math that fits your hardware setup precisely. If you take the time to try and tackle the problem, I'd be interested to know. 

  One commercial option is C-Nav DGPS (full disclosure, this is a branch of the company I work for - hence my familiarity.) It is a subscription based service, and obtains accuracies on the order of 10cm (or better.) Obviously such a service might be overkill for most hobbyist level financial commitments. If you are at all interested: http://www.cnavgnss.com/site.php

  Wikipedia also has a well written article on D-GPS - its interesting to note the availability of a cheap DGPS system usually requires an organization the size of a government - and commercialization in the popular consumer market of this technology is likely difficult with export restrictions in existence (similar to the IMU industry.) 
• CarlT February 11, 2013 at 8:14pm

  Has anyone ever tried to use two GPS, set a couple of feet apart from each other to get a more precise GPS location? 
• ben February 11, 2013 at 5:21pm

  arghh. i hate not being able.to help test lol . soon tho hopefully hehe
• Admin

  Thomas J Coyle III February 11, 2013 at 4:40pm

  Hi All,

  I have been playing around with my HIL today and I loaded in Linsu's latest ArduRover2 v2.30 eyenear code from the GitHub. I got the compass, which is the older HMC5843, calibrated to within a degree or two of Magnetic North. I did notice that the roll horizon is tilted -2 degrees to the right in the MP. Has anyone else seen the same thing?

  I experimented with the Oilpan Airspeed/Sonar input by connecting my Sharp IR sensor and found that at infinity the sonar test value is ~292 and up close is ~756. Too bad that the ArduRover2 code does not use the Acoustic Sensor ADC input for ranging or all we would have to do is change the sonar distance conversion code to that of the IR sensor.:)

  I also found that the MP 1.2.34 fails to upgrade to 1.2.35 about 2/3 of the way through the upgrade process.

  Regards,

  TCIII
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  KM6VV February 9, 2013 at 4:00pm

  @Thomas,

  I've got a video camera, and I played around with mounting the JVS video cam on my 'bot.  Not hard to mount, 1/4-20 camera thread, and I've got a few optical bench mounts.  But if anything happened, it would probably be destroyed.  Better to buy a sports camera for on-board.  I too want some video for U-Tube, I just need to make a better photographer of my wife.  Or get my son over to shoot.  Can't operate the R/C (initially) and the video camera at the same time!

  Alan  KM6VV
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  KM6VV February 9, 2013 at 3:53pm

  @Ben,

  Look forward to doing some experimenting with the new GPS module, and the compass.  I probably know just enough to be dangerous.

  You mention porting IMU/DCM code back to your 'bot, I'd consider porting the same into ROS nodes.  Also odometery. 

  I saw the compass selection w/ declination, so looks like one could do without.  I've got a lot of study ahead of me! 

  Do you know about the Sparkfun 9DOF IMU?  I think Jordi was involved with it as well.  Just need to get something going for now, but my real goal is to be involved with all of the parts, and on ROS with it.

  On ROS I get quick access to LiDAR and USB Cameras.  OK, I'm not currently looking to do SLAM, but I want the LiDAR for obstacle avoidance, and the Camera for blob detection.  And ROS can already do waypoints.

  I wonder if there is anything in the Robomagellan rules about running differential GPS?

  Alan KM6VV
• Admin

  Thomas J Coyle III February 9, 2013 at 2:00pm

  @ben,

  Since my wife is the offical home photographer I keep forgetting that I have a GoPro camera that I can mount on my E-Maxx. I will try and use it tomorrow to get a shot of my 6WD in action. Hopefully no one will be parked on my course tomorrow! LOL.

  Regards,

  TCIII
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  Bot Thoughts February 9, 2013 at 2:00pm

  @Alan, @Thomas: last time I looked at an ArduPilot derivative (which was about a year ago) as well as MatrixPilot docs. I am pretty sure the magnetometer heading, like GPS heading, is used to correct for gyro drift. I recall vaguely that the code had provisions for running with or without the compass.

  My own experimentation with GPS involves SiRFIII and Venus 638flpx units and in both cases, I got GPS heading data above some low threshold. The Venus, for example, starts reporting reasonably accurate heading above 2m/s. That heading is enough to correct gyro drift. Perhaps the same is true for your GPS.

  Both GPS modules reported heading data with a 1 second lag. I compensated for this in my custom autopilot code. I vaguely recall some code in either MatrixPilot or ArduPilot that did some lag compensation but that may have been compass lag, now that I think about it. For rovers making sharp turns, GPS lag must be addressed in some fashion.

  Bottom line, compass can help or can hurt, but can be replaced by GPS if either turning is slow and gentle or gps lag is compensated for. Magnetometers can suffer from local -- like, meter by meter -- interference as well as miscalibration etc. That's why I never used one.

  Two of the top 3 AVC finishers didn't use a compass -- one (Minuteman) didn't use GPS either, just gyro. The results were quite comparable to the top finisher that was running $1000's worth of industrial grade gyro and gps.

  I'm very interested to hear more about the specifics of what is possible specific to ArduRover code. How it uses GPS heading and compass, etc. At some point I'll have to take a peek at the code again as I may port the IMU / DCM stuff to my rover again to do 3d instead of 2d this year. We'll see :)