Which is the best GPS module for UAV's ??? [Archive]

JettPilot

Oct 31, 2006, 10:05 AM

I just bought the EM-406 SiRF III GPS module, it seemed like the perfect thing for a UAV project until last night when I read that there is a 2 second lag in the update information for this module :mad:

I REALLY like the 4 HZ update rate of the UBLOX :D , but they dont not seem to sell a complete board. By the time its all said and done, I buy the antenna, the board, and whatever else and the UBLOX is almost 200 bucks :censored: They seem to be selling mostly chips, I need to buy a module that I dont want to make a PC board, and surface mount everything... :(

The Garmin GPS-18 looks good, but it has a built in magnetic base which makes it much larger and heavier than I need it to be. I use Garmin Geckos and the update rate at 1 HZ is not great, but it is acceptable...

Anyone know of a good small GPS module that works great out of the box ? Or a cheaper place to buy a complete UBLOX module ?

JettPilot

danstrider

Oct 31, 2006, 01:00 PM

Hi Jett,

What output do you need from a GPS unit? Serial NMEA? I'm not sure what the Gecko outputs ... the 4Hz uBlox outputs in a proprietary UBX format and will take effort to integrate into a NMEA system, unfortunately. However, its 1Hz output can be configured for serial NMEA.

My familiarity is with the SamLS unit. I also made a carrier card to get from TTL to Serial voltages with a max232 level shifter. Then I found out about the 4Hz UBX format. I *think* the 4Hz is simply an interpolation of the 1Hz data, though the newer units include accelerometers to assist in making an intelligent interpolation.

Dan

JettPilot

Oct 31, 2006, 01:29 PM

I need NEMA serial output. I do not want to get so complicated that I have to hook up converters and the like. I dont want to mess with external antennas either, I just want something simple and small that outputs serial NEMA I can wire to my OSD boards and Navigation...

The Garmin GPS 18 puts out serial NEMA at 1 HZ, maybe just taking the case off it would make it small and light, and work well... Any one tried this unit yet ? Is there any delay built in ?

The SIRF III is an awesome unit, and with the development board does exactly what I need it to, but that 2 second delay will make it useless in a UAV :mad:

JettPilot

docphi

Oct 31, 2006, 04:07 PM

The delay is very noticeable in flight. I'm also looking for a small GPS unit that updates quickly.

kd7ost

Oct 31, 2006, 04:16 PM

The only plug and play unit I'm aware of is sold by UNAV.

http://www.u-nav.com/PGPS-SS.html

It's already configured and cabled. Otherwise the GPS18 is another good OEM choice. Depends on how much weight you want to save. The GPS18 comes in a tough case with a magnet built in for roof mounting on a vehicle. That's a lot of mass for a small plane. You might destroy the unit tring to get it out of the case? I dunno. Never tried it.

Dan

dalbert02

Oct 31, 2006, 04:32 PM

Does anyone know the refresh rate of the Geko 201? Curious since that is what is recommended by RC-CAMs OSD and the AP-4 autopilot.
Thanks,
-dave

kd7ost

Oct 31, 2006, 04:50 PM

Does anyone know the refresh rate of the Geko 201? Curious since that is what is recommended by RC-CAMs OSD and the AP-4 autopilot.
Thanks,
-dave

1/2 hz. One string every 2 seconds.

Dan

JettPilot

Oct 31, 2006, 05:18 PM

1/2 HZ :eek: I have used the Gecko 201 and never realized it was that slow, but I just timed the updates in one of my videos and Dan is right :mad: That being said, the 201 works fine with my UNav PDC-10 autopilot. Just dont set the sensitivity up to high and it works very well :)

I will buy the GPS 18, and try to get the case off. If it works, I can double my update rate with it, that would be awesome :D

Garmin just came out with the GPS 18 5 HZ, has NEMA format and is about 220 bucks but the update rate is faster than anything else out there. Here is a place that sells all the garmin stuff cheap:

http://www.gps4fun.com/main_store.php

They have very fast shipping, and I bought the wrong thing one time and they happily did an exchange.

JettPilot

typicalaimster

Oct 31, 2006, 05:42 PM

kd7ost

Oct 31, 2006, 05:47 PM

Good info from both of you. Thanks guys.

Dan

JettPilot

Oct 31, 2006, 07:12 PM

You have a couple from this store..

http://www.mightygps.com/oemgps.htm

They have a 1HZ refresh rate. In fact after taking the shrink wrap off my U-Nav GPS unit that one of them is the OEM they use..

Great page, and lots of neat GPS units ! I am still trying to figure out which one on that page U-Nav sells though :confused:

JettPilot

JeffElecRC

Oct 31, 2006, 07:13 PM

The SAM-LS from U-Blox is the 4HZ GPS with a more RC-friendly package. It has a ribbon-cable output, but this is very fragile. What I've done is desolder the metal shielding on the back of the unit and solder 4 wires directly to the VCC, GND, and the TX/RX pins. This isn't too difficult if you have the tools. Hot air is required to remove the metal can without destroying it, otherwise it can be cut off. A microscope would help too.

As far as I know the 4HZ position update rate is real. Their documentation doesnt say anything about interpolation. danstrider, can you tell me where you saw that it was interpolated. The Paparazzi guys are using these modules with great success. I will be soon too.

hugo_vincent

Oct 31, 2006, 08:24 PM

the 4Hz uBlox outputs in a proprietary UBX format and will take effort to integrate into a NMEA system, unfortunately.

Yes, it is binary, but if you are writing the software, the UBX protocol is much easier and less CPU-intensive to decode than NMEA. I have some code for UBX decoding, based on the code in Paparazzi if it is of use to anyone.

typicalaimster

Oct 31, 2006, 08:42 PM

I am still trying to figure out which one on that page U-Nav sells though :confused:

http://www.mightygps.com/oem/40smls.htm

USED to be their Pico-GPS. Looks like they have changed OEM's recently. Hey for $38 a unit when he orders 100 and then sells them for $150.. You can't beat that ;)

d_wheel

Nov 01, 2006, 09:03 AM

but that 2 second delay will make it useless in a UAV

JettPilot

Although faster rates are desirable, saying that once every 2 seconds makes it "useless" is a bit harsh. We have been using this rate for years and getting acceptable results.

Later;

D.W.

Unterhausen

Nov 01, 2006, 09:13 AM

JettPilot
I'm a little concerned with a 2 second delay. You get a reading every second, does that mean it's 2 seconds old?

JettPilot

Nov 01, 2006, 09:56 AM

I have not flown my Sirf III GPS but here is what Reedchristanson reported in his testing :

When we first saw this unit, we thought it was a very attractive little setup. Integrated battery, 25 mm patch, tight package, good connector, etc.

So we bought a bunch to try them out.

The good news is they have very good sensitivity. Tracking sats indoors, 10,11 sats outdoors.

The bad news is that the heading and position estimate is designed for automotive use. It is very filtered (almost 2 seconds behind another GPS unit we tested it against). This makes it very dificult to use with a UAV.

We really wanted it to work, so we spent a few days trying lots of tricks (using position output to calculate heading, etc) In the end we decided to not use it (we have a few we will sell for cheap!)

I called an engineer who put the unit together. He said their was not much we could do. It does come with software to allow you to tweak a few things, but unfortunatly, unlike the u-blox, you cannot change the filtering on position or heading.

Reed

kd7ost

Nov 01, 2006, 10:09 AM

Here's a video of mine showing the geko in operation. Given the slow speed of my aircraft coupled with the fact that position information in my typical missions are lined up on from several hundred yards away, it works well for me.

You can watch the refresh rate on the OSD unit in the video. It's driven by my Garmin geko 201 GPS unit.

http://media.putfile.com/Typical-Ag-Mission

Dan

Hamanu

Nov 02, 2006, 11:39 AM

Hey JettPilot, the Pico-gps that U-Nav sells is a gps 18 It's just taken out of the case and shrink rapped. I talked to the guys there and that is what they told me. Also I have a gps 18 that i took out of the case it identical to the pico-gps receiver. Some how I damaged it. I was able to get it to work in the case but when i took it out something got damaged. If u want i can post a pic of the gps-18 out of the case.

Hamanu

Nov 02, 2006, 12:13 PM

Typicalaimster, What osd board are you using? And what gps from mighty gps receiver are you using?

JettPilot

Nov 03, 2006, 01:13 AM

I ordered a GPS 18 :) I was considering taking it out of the case, but maybe I should reconsider that !!!

Was it hard to get out ? How did you do it ? Do you know what got damaged in the process ?

JettPilot

Hamanu

Nov 03, 2006, 06:22 AM

It wasn't hard to get out I had to pry the casing apart. The only problem was the wire casing and even with that u just have to be careful when u split it open. I don't know what got damaged I was being extra careful but some how something still got damaged. All i can say is it worked while it was in the case and when i took it out and hooked it up it didn't work. It didn't appear to be any damage to the unit but its not working so some how i screwed it up. But it wasn't to bad a hit i got it off of ebay for 50$. I just try to find another from ebay. But i am thinking about getting one from mightygps.com they look kinda promising. There were a couple of them that seemed to be ok. I dropped those guys an email but i haven't heard back from them yet.

docphi

Nov 05, 2006, 10:51 AM

JettPilot

Nov 06, 2006, 02:43 PM

Hey JettPilot, the Pico-gps that U-Nav sells is a gps 18 It's just taken out of the case and shrink rapped.

I got my Garmin GPS-18 and pryed the case apart. It just has some rubbery like glue on the seam and it came apart easily without damaging anything. When I got the case off, I found that the plastic case is a very LIGHT and only small part of its total weight.... So I put case back on !

I never liked the magetic base, so I got a small screwdriver and pryed the 4 little magents out while I had the case apart which are also just glued into the inside of the plastic base. Now the module is protected, no magnetic field, and saved some weight not carrying around magnets.

The GPS - 18 works great. 1 HZ update rate :D

The large Black wire is ground, the large Red is +5 Volt power in, and the White is Data out. The rest were not needed.

Does anyone know if WAAS is enabled by defualt in the GPS 18 ???

JettPilot

docphi

Nov 06, 2006, 07:05 PM

Jettpilot,

Would you happen to know which way the wires run inside the case? Is the green wire on the right or left side of the connector?

kd7ost

Nov 06, 2006, 07:25 PM

Does anyone know if WAAS is enabled by defualt in the GPS 18 ???

JettPilot

Yes it is.

It's also good to know it came apart so easily. I have a friend that about sliced her thumb off trying to cut it open. It wouldn't pry apart. That was about a year ago though so maybe they made some changes.

Dan

http://www.garmin.com/products/gps18oem/

JettPilot

Nov 06, 2006, 11:35 PM

The key is to use a small screwdriver, and pry the upper part up from where the cable comes out of the unit. Using the screwdriver as a lever Pushing down on the rubber cable protector where it exits the disc, and up on the seam. The top popped right off, no damage :D Which was nice when I decided to just take the magnets out and put the plastic case back on. Its like it was never taken apart.

JettPilot

clolson

Nov 07, 2006, 11:18 AM

Just lay it on the ground and inadvertanty step on it. The top pops right off ... worked perfectly here anyway. :-)

Curt.

docphi

Nov 07, 2006, 12:43 PM

Guys,

Does anyone know what side is pin 1 and 6 on the board? I called Garmin, but, they said they couldn't help. :rolleyes:

JettPilot

Nov 08, 2006, 12:02 AM

Do you still have the little plug that goes to the GPS board ? I can tell you by color what each wire does :)

JettPilot

docphi

Nov 08, 2006, 06:06 AM

I have the plug. I know what each wire does. I just need to know which pin is pin 1 on the board itself. I removed the wires from the plug and mixed them up by mistake.

JettPilot

Nov 09, 2006, 12:39 AM

I wish you had asked me that a couple days ago, I could have taken a picture. The disc is put back together and sealed inside a wing... If there is no other way, one day I can cut into the wing and take a picture for you, but it will be a lot of work... So try this first.

I bet Hamanu still has his Garmin 18 apart and can tell us where those wires go. I would PM him.

JettPilot

brianhomer

Nov 10, 2006, 09:30 PM

For more flexible (means you want the whole UAV system starting from scratch), you might need some discrete module instead of completed unit. I got EM406 as well. But finally i brought extra GM862-GPS. As this is togehter with GPRS. Extra GPIO is also available and you can use SPI to connect with your controller.

kbosak

Jan 09, 2008, 09:06 PM

There is one more limitation to GPS revceivers:
60.000ft max altitude and some 1000mph max speed.
The latter is not that important until I start rocketry, but
alt limit is important to me as I want to drop a glider from meteo balloon.
Here:
http://showcase.netins.net/web/wallio/GPSrcvrsvs60kft.htm
you have some compatibility list.

To quote somebody quoting wikipedia:
"
to quote Wikipedia:

To help prevent civilian GPS guidance from being used in an enemy's military or improvised weaponry, the US Government controls the export of civilian receivers. A US-based manufacturer cannot generally export a GPS receiver unless the receiver contains limits restricting it from functioning when it is simultaneously:
(1) at an altitude above 18 kilometers (60,000 ft) and
(2) traveling at over 515 m/s (1,000 knots).

To meet that specification, it is easy for them simply to stop giving output at 60,000 feet and not have to worry about the speed.

Using a GPS *NOT* manufactured in the USA may help.

Mac
"

I have trouble finding a GPS with 4Hz update and without 60Kft limit.
u-blox documentation says nothing explicitly, maybe do you know that u-blox has this limitation and I can stop searching desperately and switch to 1Hz unit like Garmin 18?

For sure EB-85A is limited to 18000m, confirmed by manufacturer upon request.