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GPS City Q&A » OEM GPS » Would this work for a marine robot?

OEM GPS (8 replies)

Item

Original Question

Would this work for a marine robot?

› Garmin GPS 18x High-Sensitivity LVC

Author

Reply

Jianxun
East Lansing, MI

Original question asked on Apr 22, 2010, 5:36pm

Dear Sir or Madam,

hey, this is Jianxun, a PhD student. I would like to buy some GPS receivers from you. I'll fix it on my robotic fish and it should provide a feedback position signal. I know it should have a good performance with WAAS signal. While I wonder how good it works if through regular satillate logging. I don't care the absolut error very much, while I do want to have a relative correct distance when the model moves.

Thanks,
Jianxun

GPS City
Calgary, AB

Reply #1 on Apr 23, 2010, 10:50am

Hello Jianxun,

This unit will output NMEA 1083 at 1 Hz to your Robotic fish. You would need to tow it on the surface, because when you get a few cm below the waters surface with the 18x GPS antenna it will stop working. GPS doesn't work well under water. Others have done it by having their underwater robot surface from time to time to get a position lock. The unit has great reception when above water.

Cheers
Jordan

Jianxun
East Lansing, MI

Reply #2 on Apr 23, 2010, 11:39am

Dear Jordan

Hey, thanks for your reply. I really appreciate. I have two more questions. First, what's the position of antenna in the package. Our fish is on the surface of water and the top of is should be 2 or 3 cm above. I'll put your GPS in the body. So I want to make sure how I can let the antenna above or near the surface. Another thing, the fish should be deployed in a 100m by 100m pond and need the position signal to feedback. It needs a relative precise position signal to realize position control. Do you think it's possible for your product.

Thanks,
Jianxun

Jordan GPS City
Las Vegas, NV

Reply #3 on Apr 23, 2010, 12:15pm

Hello,

This is a sensor, so the board and antenna are one module. you can not easily add a external antenna to it as is. You may want to look at the OEM 15 series and then use an external antenna like the Garmin GA25MCX.

Because you want really precise control of the robot you will probably need to do some GPS magic and the Garmin device wont work for you I think. You will need a device that outputs binary pseudo range code. The USGlobal sat modules like the MR-350 would work a little better.

Here is a RTK c library for getting more accurate positioning with the MR-350p

http://gpspp.sakura.ne.jp/rtklib/rtklib.htm

Cheers
Jordan

Jianxun
East Lansing, MI

Reply #4 on Apr 24, 2010, 5:39pm

hey,

Thanks. I'll consider the models you suggest as well.

I do want to learn more about the Garmin one. I don't want to attach an extra antenna for it. I just want to know the position of antenna in the package, s.t. I will make the antenna on the top of my robotic fish. In other words, I can make it work more efficient through changing the orientation. Another thing, Does it work as good as 18x_5Hz(except update rate). Are the accuracy of these two models the same?

Thanks,
Jianxun

Jordan GPS City
Calgary AB

Reply #5 on Apr 25, 2010, 8:00am

The antenna is positioned at the top. So the antenna sits parallel with the sky. For navigation of autonomous vehicles it is better to have a high update rate. When it comes to reception they are pretty much on par with the exception of the update rate of course. The accuracy is the same and should be 3m 95% of the time with WAAS enabled.

Cheers

John Thon and Jianxun
Michigan State University

Reply #6 on Apr 27, 2010, 2:31pm

Hi Jordan, My name is John Thon and I am the school teacher who is responsible for packaging the robotic fish that Jianxun is building. Jianxun is hoping that the Garmin 18X could be turned vertically in our robot. He is interested in knowing if the GPS antenna inside the unit is a coil or square. I believe that he is concerned about the unit being placed horizontal, and is trying to inquire as to if the antenna could be mounted vertical and inside our fish. His main concern is the profile of the robot, it is small and he hopes it could be placed vertically in the robot. If you could help us identify the exact location and type of antenna inside, relative to the cable, we would use this to information to present our idea of placing only this specific portion above the water, within the body shell. Our hope is that it could be vertical and placed up, slightly out of water but encased in our fiberglass body. Is this possible or is the only way to position the GPS, parallel to the sky and 2cm above the surface of the water? Finally, is the encasement of this unit in fiberglass a problem?
Respectfully, John Thon, Holt Junior High School

GPS City
Las Vegas, NV

Reply #7 on Apr 28, 2010, 6:43am

Hello

The unit should work on its side but you may see a degradation in the DOP because the base of the unit may block that side of the sky's satellites. You may want to investigate the Garmin OEM15 series. It will allow you to position it better. The oem 18 is a enclosed package that you wont want to dismantle.

You can a OEM15 get one that talks CMOS that you may be able to integrate directly your controller. The other reason to go this way is you can get a smaller profile antenna that wont take up as much room as the OEM 18x.

OEM15 http://www.gpscity.com/search/q=oem15
I included a link to all the OEM15 just incase you need different communication types.

The next part you need with the OEM15 is an antenna. The Garmin GA25 works nicely.

http://www.gpscity.com/garmin-ga25-mcx-antenna.html

Cheers
Jordan

Jordan GPS City
Las Vegas, NV

Reply #8 on Apr 28, 2010, 6:44am

One more thing fiberglass should not cause to much problems depending on the construction. Metal bracing and if it is too thick may be an issue. But for a small robot you shouldn't have to worry.

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