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Old Apr 20, 2005, 05:50 AM
Joel Haasnoot
Leiden
Joined Mar 2005
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Small, Cheap GPS Modules

This came up in another thread, but does anybody know what cheap, small GPS receivers are availible. Really, as long as I can get UART / RS232 I am happy, I could further process the data. Really, I'm looking for parts under $50. Any ideas?
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Old Apr 20, 2005, 03:09 PM
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Mr.RC-CAM's Avatar
USA
Joined Oct 2001
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Sparkfun: http://www.sparkfun.com/shop/index.p...227641&cat=63&

Like all the other affordable GPS module offerings I have seen, these don't have the traditional waypoint features. Waypoints reduce the software complexity of the host quite a bit. So, be prepared to code that part on your own.

RC-CAM
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Old Apr 22, 2005, 08:11 PM
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Here's something I've been wondering: is there any reason why some of the very small GPS units wouldn't perform as well as larger ones, simply as a function of size?

For example, this Garmin GPS25 is nearly 3" by 2" and weighs almost 1.5 ounces, and it's what I was originally considering. Now I've been seeing these small u-blox modules and others (with not quite the performance of the u-blox) that are literally about the size of a penny, without antenna.

Is there any reason why these tiny guys might not be able to acquire the satelites as well, or in other way not perform as good? I know I can look at the spec sheets, and they say they work alright, but somehow something that small doesn't look like it could.

Maybe I'm just incredulous.
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Old Apr 23, 2005, 02:32 AM
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Cedar Rapids, IA
Joined May 2003
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I have the ublox RCB-LJ http://www.u-blox.com/products/rcb_lj.html and it works great. It is kinda on the expensive side, but it is fully configurable, which is really nice. It also has a 4 hz update rate... Rotomotion uses one of the ublox modules in their autopilot...

Matt
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Old Apr 23, 2005, 04:04 AM
Joel Haasnoot
Leiden
Joined Mar 2005
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OK, the small doesn't matter too much... as long as it's not tooo expensive (i.e less than $75)
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Old Apr 23, 2005, 06:18 AM
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$120 for 4hz and UTM output, u-blox is worth it.


Ram.
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Old Apr 24, 2005, 04:48 PM
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Switzerland
Joined Sep 2004
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How about this module:
http://www.falcom.de/txt-produkte-navis-k.html

It uses the SiRF chipset, and can be purchased for about 72 Euros. It's a small module that can be easily mounted on the top of the plane. Contains built-in battery backup, and only requires a 5v supply. It's interface is RS232, NMEA supported.

Now, for the update rate... it would appear that it contains the SiRFStarIIe chipset, which is specified at 10Hz update rate. It's not clear how to get it into this mode though, data sheet is here: http://www.falcom.de/pub/MANUALS/SiRFmessages.pdf
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Old Apr 25, 2005, 12:11 AM
Gotta make the doughnuts
Toledo Express, Ohio, United States
Joined Oct 2004
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I've seen some SiRF chipset GPS modules with NMEA on Ebay for as little as $16 USD. They weren't the highest end, but the ones I've seen that support ranges within 3 metters went for about $40-50 USD.
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Old Apr 29, 2005, 03:43 PM
JettPilot's Avatar
Miami
Joined Apr 2005
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Here is a great little GPS module, has waypoints and all the features and software you want

http://www.gps4fun.com/gar_gps18.php
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Old Apr 29, 2005, 04:17 PM
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Quote:
Here is a great little GPS module, has waypoints and all the features and software you want
Nice little package. I don't think it has internal waypoints -- that feature seems to be performed on their external PC software (enroute).

RC-CAM
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Old May 06, 2005, 11:20 PM
JettPilot's Avatar
Miami
Joined Apr 2005
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You are right, it does not have waypoints . What GPS to you guys recommend to hook to an autopilot to control altitude and heading ???
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Old May 07, 2005, 01:02 AM
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Nampa. Idaho
Joined Nov 2004
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I think it depends on a few issues. One is how you're going to power it. There is a Garmin GPS 12 that some folks use. It's big and heavy though. The software in it allows for a Round Robin type route if your following that type of flight pattern. (Who isn't if flying autonomously?) All newer GPS's have some idiotic function called "Smart route finding". It's a workable issue though in some or most types of flying. No hand held GPS that I'm aware of will repeat consecutive waypoints. It won't go back and fourth so you can't program it to fly someplace, loiter for a while between the same waypoints, then return. That's because of the GPS software and that "Smart route" function. I use the Garmin geko 201, but I power it from an external 3.7 vdc LiIon battery through a 3.3 volt LDO regulator. The geko uses a pair of AAA batteries internally and go's through them very fast. Very, very fast. Not a good thing. (You don't want to fly in power save mode in your GPS because it slows down the refresh rate quite a bit.) If you don't want to use external power, I would go with a basic Garmin eTrex. The Yellow one. It takes AA batteries and you can get those as LiIon AA cells. They last a very long time. You just have to learn how to get through the "Smart Route finding" function. Let me know if your interested in that and I'll post more. It's a bit of a story. The geko also has front panel buttons. It's easy to open a hatch and access the unit's controls without pulling it out of your craft. A blind GPS like the 18 will stay powered up as long as it has power. I have a GPS 12 and it shut down due to vibration. I've never had a geko shut down in flight. I watchdog the GPS unit with a basic stamp and a micro servo. If you loose power to a geko or eTrex, then power it back up, it will still be navigating it's course. If you loose power to a 12 and power it back up, it's no longer following the goto or route. I don't like that at all. Pro's and con's. We got em.

Edited to include the following.

The geko can be operated with WAAS enabled. This gets altitude a lot closer to being accurate. The eTrex doesn't have WAAS due to it's vintage.

I use the geko with external power through the serial port. I find it has the least amount of crucial shortages. I also use it just to come back to me so am not using the Route function. The Pico Nav unit from U-nav is really a nice unit. It solves these problems. I think it's worth the cost and they addressed these significal problems. That product give's some real advantages in a true UAV mission world. I'm sure they had quite a bit of engineering cost put into it.

Dan
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Old May 07, 2005, 02:11 AM
JettPilot's Avatar
Miami
Joined Apr 2005
10,883 Posts
Thanks quick answer Dan,

I was looking at the GPS 18, but I would need a Pico Pilot to run that and for altitude and nav they want something like 800 bucks , thats just more than I am willing to shell out. I was looking at an Etrex, but from what you have told me, I think the Gecko is the way to go . I dont mind using a regulator to power it, where can I get one ? I am running a 12 volt system. The main thing I want the GPS to do is overlay its info on my video link, and bring the airplane back to the field and fly circles if I loose my video and am unable to control the airplane. I have the GPS overlay board from ICI to impose the information on the video, I assume the gecko will work with that. What autopilot are you running ? Can you recommend one that is cheaper ?
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Old May 07, 2005, 03:53 AM
Professor of Wood
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Nampa. Idaho
Joined Nov 2004
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I use this regulator.
http://www.digikey.com/scripts/DkSea...330214&Site=US

The geko 201 GPS will work with your overlay unit to display the information you want as well as function to get you back to your "goto waypoint". It will output NMEA 0183 data format at 4800 Baud. This is what most of these devices operate with. It's an industry standard. You will need to take the output from a garmin type connector. Check out http://pfranc.com/projects/g45contr/g45_idx.htm for after market connectors if you want to save a few bucks. There are only four connections on the plug and only three you'll need to make. + voltage will bring in your 3.3 vdc from the regulator. Output will split. It needs to go to both your overlay board and to your guidance system. The battery and guidance device need to have their common tied together and connected to the geko - input. I will have a NEW PDC-10 in a month or so for sale if you want one of those. It will be $ 115.00 + shipping but doesn't include an altitude lock. It follows the GPS information and steers the rudder. You will need a co-pilot or similar for roll control and some form of altitude lock to complete the package. I can sell you a PDC-20 altitude lock if you need it but those are prime and rare. It will be $ 150.00 for that unit if you want it. If you aren't going very far, the co-pilot should serve you as long as you aren't flying real close to the ground. It will stabilize pitch, but won't keep altitude. Your plane will be subject to sink and thermals.

Dan
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Old May 07, 2005, 05:33 PM
JettPilot's Avatar
Miami
Joined Apr 2005
10,883 Posts
Hi Dan,

The PDC 20 sounds like exactly what I am looking for I am going to be flying long distances so altitude lock is something I definately need. You can email me at orcabonita@hotmail.com and I will send you a check right away. I will also order my gecko today. I looked at the digikey site, i guess I will have to build the regulator ? Is that the switching regulator that is 85% efficient ? Im sure you are familiar with the old type of regulator that just wastes its ecess power, cant have that I will be using an FMA copilot to keep the plane level. Do you suggest the new FMA8 copilot, or is the old FMA4 just as good ? I would really rather use my JR receiver than thiers... Thanks for all the info, I would have been looking for a long time to find a good combination of components.

Mike
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