GPS with VEX
 

As of now I have a pretty complex Vex bot with a variety of sensors. I'm interested in using a GPS receiver but I'm unsure if it'll work and how I'll be able to use it. I want to be able to use the GPS receiver to control the bot to move where I want it to go. The bot also uses ultrasonic sensors to avoid obstacles if that makes if a difference. I'd prefer to not have to buy a new microcontroller if the VEX controller can do the job. But if you're 100% it can't then I'd be interested in another Microcontroller. For programming I use EasyC and RobotC.

Any input would be greatly appreciated.

Thanks

Re: GPS with VEX
 

GPS reccivers traditionally output NMEA 0183 sets of data over a serial port. I'm sure you could decode the data and read it using a vex controller. A good overview of the output of a recciver is Here

Re: GPS with VEX
 

I don't know if the Vex controler can support serial communication because I've never used vex before, but there is a a good gps reciver at http://www.parallax.com/detail.asp?product_id=28146 . I know my team was contemplating using this for our frc bot. If the vex controler does support serial communication then you just have to write some protocol code for the reciver and you shouldent have any problems.

Re: GPS with VEX
 

Yea I've been reading up on NMEA over the past few days. I was looking at this GPS reciever http://www.parallax.com/detail.asp?product_id=28146 but I was unsure if the VEX controller would be able to decode the input to be able to control the robot. I talked to a sales rep from Parallax and he was unsure as well.

Re: GPS with VEX
 

People have used the CMUcam with a Vex controller over serial so you can defientely do it.

Re: GPS with VEX
 

The Vex controller has 2 serial ports available. The port 2 is unused and could be used to interface to the GPS unit. It is a 5 volt TTL serial port. The Parallax GPS is 5 volt TTL and would be compatible with the Vex port. I don't remember there being serial port support in easy C however WPLib does support serial if you want to use Easy-c. Note that this an older GPS unit and probably will not work well indoors.

Re: GPS with VEX
 

The Vex microcontroller only has 1 serial port that I can see. But the Parallax GPS reciever, from what I can see, works with the board ports and I'd be plugging it into the rx port I assume. I guess my main problem now would be how to code it since EasyC would most likely not work. Not exactly sure what WPLib is but I also do have Carnegie Mellon's RobotC. If you could elaborate more or maybe hit me up on AIM or something that would be great.

I also noticed another good GPS unit thats being used a lot called the eTrex made by Garmin. I'd most likely need a new microcontroller which isn't the biggest problem in the world though I'd like to stay with VEX because I already have all my sensors coded and hooked up the way I want them. But the GPS at this point is more important and I'd be willing to make a change if neccessary.

Re: GPS with VEX
 

I believe Easy-C pro does support serial. The functions are there but may not be exposed. I don't have Easy-C pro. Maybe some one could cjhme in or post a question in the easy-c pro sub forum.

Re: GPS with VEX
 

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.

Re: GPS with VEX
 

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

Re: GPS with VEX
 

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

Re: GPS with VEX
 

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

Re: GPS with VEX
 

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?

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.

Re: GPS with VEX
 

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

Re: GPS with VEX
 

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.