GPS with VEX

[artdutra04]

WPILib is the framework written by Brad Miller at WPI (hence the name) from which EasyC is based on. You can program using WPIlib in either EasyC PRO (because it supports custom .c files and has a built-in text editor) or any other IDE of your choice. (MPLab, Eclipse, etc). Every time you use something like StartUltrasonic(); or SetPWM(); in EasyC, that's really a WPILib function.

There are currently 2 serial ports on the Vex controller - the RxTx port and the programming port. Using WPILib, you can interface with TTL devices (like the CMUcam) using the RxTx port and a TTL converter. As long as the device is 5v and outputs TTL, you should be able to write your own custom 'drivers' to read the signal on the Vex controller using WPILib.

[basicxman]

doesn't the parrallax gps have i2c, i think this would be compatible with Vex

[whytheheckme]

How accurate would GPS be? Would it be accurate enough to detect robot movement on the field?

This made me think (kinda unrelated), but what if you set up a local positioning system within the venue to track your robot on the field (I can already think of the rules that this violates), but maybe we could ask for an exception for a completely automated system, or better yet and IFI supported venue device that is universal and could be used by all teams to track their robots?

Thinking aloud,
Jacob

[basicxman]

gps is accurate enough that you could pinpoint the location of your robot in your room (i.e. what room its in)

[Kingofl337]

You would need easyC Pro to access the serial port to use GPS. I think GPS would be a really cool field positioning device for both FRC or FTC. I just don't know enough about how you could create your own field based GPS network. Would be cheaper to use ZigBee modules to pinpoint a location based on signal strength?

doesn't the parallax gps have i2c, i think this would be compatible with Vex

Unfortunately IFI didn't bring out I2C in the VEX controller other then it is used by the two PICs
to communicate with each other.

[basicxman]

Originally Posted by Kingofl337

Unfortunately IFI didn't bring out I2C in the VEX controller other then it is used by the two PICs
to communicate with each other.

doesnt matter, you can use standard I/O pins and make subroutines for i2c, look at this topic in the VexForum (www.vexforum.com), i've already posted how, after FIRST i'll even make the subroutines

[SgtMillhouse648]

Originally Posted by basicxman

gps is accurate enough that you could pinpoint the location of your robot in your room (i.e. what room its in)

maybe what room its in, most GPS units I know are accurate to only about 10-20 feet of so.

[jgannon]

It's worth noting that the quality of your GPS signal is substantially deteriorated if you don't actually have line-of-sight to the sky, so even with an exceptionally accurate GPS unit (some models have sub-meter resolution, though most likely not within the FIRST expense rules), it'd be pretty hard to ascertain your position inside an arena. However, making an outdoor robot with a GPS is pretty sweet.

[whytheheckme]

So.... what are the odds of IFI issuing some kind of field positioning system (weather its a beacon in the center of the field, or some kind of magic sensors under the carpet) and the devices to use in our bots?

I think that while the lights are a challenge, they simply aren't accurate enough. Imagine how much more complicated the game could be if you could reliably know where your robot is at all times.

Jacob

[AdamHeard]

Originally Posted by whytheheckme

So.... what are the odds of IFI issuing some kind of field positioning system (weather its a beacon in the center of the field, or some kind of magic sensors under the carpet) and the devices to use in our bots?

I think that while the lights are a challenge, they simply aren't accurate enough. Imagine how much more complicated the game could be if you could reliably know where your robot is at all times.

Jacob

In 2004 there were two infrared beacons that could be used.... From what I remember, most teams didn't because dead reckoning, line following & gyro and/or encoders all worked better. Anyone with more experience care to clarify?

How is the light not accurate enough though? Between this year and last year we had distance down to less than a foot of accuracy, and the angle wasn't too bad either (I don't remember exactly). I can't imagine any field based navigation being any more accurate.
EDIT: didn't realize you were talking about the entire field, not just an object...... In that case, I can't think of any current system that is realistic for FIRST that will work here....

[whytheheckme]

I was thinking about a radio transmission system that works like a local GPS, where something above the field is transmitting a signal, and devices on the robots can use the exact timing of that signal to determine exactly where it is (think thats how GPS works, but i could be completely wrong.) Something radio, wireless, free of looking for visual things (or infrared, basically free of line of sight stuff.) More of an actual location instead of an estimated calculated location. Think of the possibilities for a game and the autonomy of a game if you had this data reliably!

(I just realized that I'm talking about FRC here, and the thread is titled VEX. Sorry for the confusion.)

Jacob

[dtengineering]

Here's a couple ideas to kick around... rather than using a radio signal, why not an ultrasonic signal? Since sound travels more slowly, it is a bit easier to measure the timing differences accurately. If there were four transmitters (one in each corner of the field) and each fired a slightly different length of noise at a pre-defined interval, it may be possible for the robot to determine its position with a fair bit of precision... barring reflections and other nastiness.

Or take a couple of CMUcams (or perhaps something with a bit higher resolution) and point them up at the ceiling... use some of the fixed field lighting as "stars" for an "astonomical" positioning system. It would require a fair bit of effort to deal with blinking and moving lights and such, let alone lens flares and other real-world weirdness, but in the happy, happy world of pure theory... it might work.

But anyways, that is off the point of the thread... my Garmin Etrex Legend has an RS-232 port and should be able to "talk" to a VEX. Although I've only used it for downloading track logs and uploading maps, I believe it IS capable of doing a real-time GPS location feed. The downside is that it has an older chipset... I've found the new SirfStar III devices to have much faster acquisition times and better reception. Some of them even work indoors.

There are also neat tricks for improving GPS accuracy. One of the less expen sive ones... although not a particularly useful one for real-time robotics applications... is to leave your GPS sitting in one place for an hour or so and record all the positional readings (they will fluctuate a bit). Then you compare them to the readings of a nearby receiver at a known location. Since some of the errors in your signal are caused by random atmospheric fluctuations, and since a nearby receiver will have similar fluctuations, then the errors between the two sets of readings should be similar. Since the reference receiver is at a known location, it will be possible to determine a known error, and modify the results for the mobile GPS unit. I suppose this technique could be modified to offer real-time benefits, but I don't know if I'd want to do that on a VEX platform.

Jason

[tseres]

Originally Posted by dtengineering

There are also neat tricks for improving GPS accuracy. One of the less expen sive ones... although not a particularly useful one for real-time robotics applications... is to leave your GPS sitting in one place for an hour or so and record all the positional readings (they will fluctuate a bit). Then you compare them to the readings of a nearby receiver at a known location. Since some of the errors in your signal are caused by random atmospheric fluctuations, and since a nearby receiver will have similar fluctuations, then the errors between the two sets of readings should be similar. Since the reference receiver is at a known location, it will be possible to determine a known error, and modify the results for the mobile GPS unit. I suppose this technique could be modified to offer real-time benefits, but I don't know if I'd want to do that on a VEX platform.

Jason

WAAS (wide area augmentation system) does this for you on relatively new GPS receivers. it takes what the satellites are giving and compares it to a known location (WAAS station)

[dasmoenator]

Thanks for the great info guys. I'll definitely be looking into WPILib. From what I hear its what I need. My project is more of an outdoors thing so I'm not too worried about GPS signal having problems with walls. I'm still somewhat torn between the parallax GPS and the eTrex. I'll probably end up with the parallax as it was mainly made for this purpose and the fact that I will be able to integrate it into my bot quicker and easier is a major plus. I'll post back with some results after I try it all out.

[Gdeaver]

There are six fixed position 900 mhz transmitters at the operator stations. There are ways to resolve your position from these sources, however it is not easy. In the past our team has used parts of the field as way points. This proved very easy to do in stack attack and raising the bar. First put lines on the field. They where easy to detect with the Banner sensors. We drove toward the line using dead reconing, stopped when the line was detected, timed turn and go on. It was good enough to nock the ball off in raising the bar. We now have a large inventory of available senors. Each year evaluate the field for waypoints objects.