Small, Cheap GPS Modules

[joelhaasnoot]

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?

[Mr.RC-CAM]

Sparkfun: http://www.sparkfun.com/shop/index.php?shop=1&cart=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

[LukeZ]

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

[mattweisz]

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

[joelhaasnoot]

OK, the small doesn't matter too much... as long as it's not tooo expensive (i.e less than $75)

[sesat]

$120 for 4hz and UTM output, u-blox is worth it.


Ram.

[AnthonyRC]

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

[Rhathid]

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.

[JettPilot]

Here is a great little GPS module, has waypoints and all the features and software you want :D

http://www.gps4fun.com/gar_gps18.php

[Mr.RC-CAM]

Here is a great little GPS module, has waypoints and all the features and software you wantNice little package. I don't think it has internal waypoints -- that feature seems to be performed on their external PC software (enroute).

RC-CAM

[JettPilot]

You are right, it does not have waypoints :mad: . What GPS to you guys recommend to hook to an autopilot to control altitude and heading ???

[kd7ost]

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

[JettPilot]

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 :eek: , 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 ?

[kd7ost]

I use this regulator.
http://www.digikey.com/scripts/DkSearch/dksus.dll?Detail?Ref=264396&Row=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

[JettPilot]

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

[danstrider]

I'm cooking up a standalone GPS datalogger and was doing some testing this early afternoon. Thought I would share a picture of U-center, a free evaluation toolkit from u-blox for use with their receivers. Sure helps me understand how good the GPS data is (imagine an auxillary plug to check out the GPS before letting a UAV go?).

I paid ~$150 to get my SAM-LS up and running. It spits NMEA format out of two serial ports. At smaller than half a credit card and a measly 1/4" thick, it's definitely smaller and lighter than the handheld GPS units .... might work well with an embedded UAV system.

Just thought I would share....
Dan

[Myron]

Hey Guys,

I have about 100 or so Rockwell Microtracker LP board GPS units.. It is just the board, so no screens or bottons... Probably good for the electronics guru's to get the pinnout and use it as a DIY type deal.. The are 31 grams and they measure 2"x2.75".
Again, it is just the board so you would have get the wiring digram/pinnouts and DIY.

Myron

[kd7ost]

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

I should clarify the Regulator issue. The geko isn't too bad on power consumption. The problem is that it uses 3.3 volt processing. With new batteries you have enough power. As the batteries start getting used, they naturally drop voltage. Once they get down to ~2.4 to 2.5 volts, that’s too low for the processor anymore. The geko says "battery low" and quits working. The batteries will still read 1.2 vdc or so each. They aren't dead till they get around .9vdc as far as non-processor based applications. So, the AAA batteries are small and hold only a little chemical energy to begin with. The geko skims the top and quits. It really isn't that the geko is a power pig.

That having been said, I use a single 3.7vdc 1400 mah LiIon battery into a 3.3 vdc fixed regulator. The geko will run straight for days on that combination. As long as the voltage doesn't drop below a certain amount, it's happy. After a typical day of several hours of being turned on, flying etc, I charge up at home. My Maha charger on that one battery takes about 10 minutes to peak it up and it only takes 40 ma or so. That's with using the fixed voltage regulator I mentioned above. It is cost effective and energy efficient to use in these types of applications. It's also highly reliable. There is no problem of course, that I can see, with using a switching regulator and further increasing the energy savings. I just want to get out that it's not a real problem to use a fixed regulator. You don't need to heat sink the one above. I haven't measured current in the geko while it's on but it isn't much.

There are 3 flavors of geko. The 101, 201 and 301. The 101 WILL NOT work. It doesn't have a serial out port.

The co-pilot I use is the CPD4. It is available from FMA for $100.00. You do need to have some form of "Enable" to work these autonomous systems. That means a radio with Failsafe and spare channels to each devices enable line. You can put a Y cable on a single channel and activate both PDC devices simultaneously, but I would rather enable the altitude lock and the GPS steering independent of each other. I like the ability to fly off a little ways and have the altitude lock taking care of me. I don't want the GPS device enabled just then, otherwise it just flies back to me and I don't get to go look at what I want. (If I do get hit or lost or whatever, the PCM enables the PDC-10 and the plane returns overhead to loiter) If either PDC device is enabled, the corresponding stick input is ignored. You can't over ride the units. When they are not enabled, they are transparent to your input. It's like they aren't there.

The CPD4 co-pilot is different. It has a couple of options for enabling. I leave the enable line disconnected. That forces it to adjust it's gain to internal setting. I use the on-board gain pot on the CPD4 to set my amount of aileron throw used to stabilize roll. (Remember, I'm not using it for pitch, The PDC-20 is on the elevator for true altitude control) You can override the roll by putting throw in the aileron stick. It's only about 50 percent or so though. Your plane will seem "Sluggish" in roll and if you let off the stick it will flatten right back out right now. You have to stand on any bank your trying to make. Fly like it's a C5 and you'll be OK. (Heck, your plane is about as big as a C5 anyway huh) ;-) You don't have to "counter" stick direction to get out of the bank.

If you don't have a PCM radio and the ability to program failsafe to enable devices, you might consider the other 8 channel co-pilot receiver combination. I haven't used it but I understand the unit uses a proprietary method of memorizing your FM transmitter signal and being able to work like a PCM radio. Don't take my word on that though. By the time I buy a 8 or 9 channel radio, I pay the extra for PCM.

From a systems integration perspective, I highly recommend the following procedure to set all this up. Go one at a time. Your flying skills become automatic as you repeat flight. You don't have to think about it anymore as it becomes instinctive. Throwing all these devices in and going for it will make you feel worse that your first solo. I recommend the following.

1. Install the co-pilot. If your not going to employ pitch, don't put it in. Just connect Ailerons. Naturally, go through the manual and make sure it is set up correctly in the shop. If you use an adjustable spare channel to begin with, you can play around with the amount of gain you need to stabilize. By looking at the picture of your plane, I presume you can go full gain. Thing is, you need to fly it in patterns you are familiar with. Do it over and over and get used to what it looks and feels like. It will be different. You can adjust out the gain if you use an adjustable spare channel. (One on a knob) If it feels too goofy, you have the option of minimizing it and it will be pretty transparent. Like it's not there. So just mess with that until you get used to it. You can remove the enable line later if you wish. (My preference. It frees up that channel so I can adjust my video camera tilt) Then adjust gain in the processor's pot, and now every time you fly it will be stabilized by that amount. You can't adjust it from the ground anymore. Spend time flying with that until it becomes instinctive. This is the easiest part.

2. Next is to put in the Altitude lock. Remember, if it's enabled, you can't input elevator from the transmitter. (That’s with the PDC-20). Again, follow the book on installing it. You need to be in the habit of standing behind your plane just before take off and looking to ensure you have rudder, elevator and aileron command before you start your take off run. Always. If you have the altitude lock enabled on a take off run, you will not rotate. You will stop at whatever you run in to. I have done that early on. Fortunately I was at a dry lake bed and I was able to let it run out with no damage. Rocks? Trees? No good. Always make sure your systems are off and you have control PRIOR to making your take off run. You have to get up to altitude, on your once again familiar flight path, and set the unit to operate. Once it's enabled, you can push and pull on the elevator stick all day long to no avail. So be ready and comfortable with pulling that enable switch off. You'll be looking to see if the plane either, doesn't stay at the right altitude, or porpoises in the range. I would start out at 50 percent gain for your plane. I'm pretty sure that will be too much by looking at your picture. It will bounce up and down at the altitude you set it at. You'll disable the PDC-20 unit, and land. Adjust some gain out and go again. This is repeated until you see it stay where you want without porpoising. It might be helpful to have someone take notes of your observations so when you get on the ground you'll remember what to do. It can be a little exciting going through this. I would recommend you make any motormouth helpers leave too. If you run out of adjustment range and still things don't work just right, you may have to make course adjustments first by changing linkage throws to get you where you need to be, or change out servo's with ones of different speeds. Then go back to the adjustment pots. Be ready to do this if needed.

Don't put the PDC-10 and GPS in yet. Now you get to learn to fly a different way. You will have to think about it. Fly up to altitude and enable your PDC-20. Your CPD4 should already be stabilizing roll. The plane will be flown in a manner that does not use coordinated turns. Just use Rudder. Steer the plane around with only rudder commands. (Keep enough throttle in to stay up but don't go all out.) Maybe 25 or 30 percent throttle. I don't know in your big bird with twin set up. Don't get too close to stall speed but don't go real fast either. Make sense? Leave the right stick alone. Don't ratchet the throttle. Just steer with rudder. It will not feel right to you and it won't look right either. But it will work. You will use up much more real estate when turning so be ready. The altitude lock will keep you where you set it. The co-pilot will keep the wings flat. Fly this way a lot till you get used to it. Enable and disable the altitude lock and keep the plane a little nose heavy. Practice doing this till you can switch back and fourth and be comfortable with both styles of flying. It's not hard as long as you take a relaxed approach.

If any of this doesn't work out just right, it's easy to manage as long as you keep it in small steps this way. Control throws may have to be tweaked to get your plane set up like I mentioned above. Some quality servos are high speed and some are high torque. (lower speed.) I use low speed high torque servos. The plane should fly looking effortless with no radical pitch, roll or yaw changes or something still isn't set right. It will take a little more airspace than before to get around. That’s perfect. It's a UAV and not a pattern ship.

The PDC-10 is the same way but I'm getting typers cramp. Lets keep this going where you're at and we'll create a written history of at least one way to get set up. Once we're ready for the GPS, we can cover that too.

Dan

[JettPilot]

Great info on setup Dan, its very informitive to know how these things act in the air rather than launching and finding out the hard way :) . Im ordering my Gecko, it sounds perfect. My power supply will be around 18 volts or so.. I think one of my biggest problems will be to find a 3 amp 12 volt switching regulator. Also I will be looking for an 18 to 3.3 volt switching regulator for the gecko. I checked the voltage graphs of NIMH batteries and they vary more than 20 % through thier cycle, my camera is rated at 10% from 12 volts, so I think a regulator will be needed. My 12 volt pack fully charged may actaully be at 14 or more volts when I switch it on, and that may be enough to blow the camera :mad: , so 18 volts and a regulator seems to be the answer. There are plenty of the old style regulators out there that waste the power, but I need all the battery capacity I can get.... 3000 MAH that I have is marginal already... I cant beleive with all the technology involved that I am stuck due to the lack of a voltage regulator :eek: .

BTW, the radio is a JR PCM10X, all the knobs and switches, I will ever need. I am leaning on getting the new FMA copilot 8 ... The servos are digital high speed and high torque metal gear.

[AnthonyRC]

Unfortunately I have to withdraw my recommendation for the SiRF based falcom NAVI-S (or for that matter any SiRF modules).
The data sheet for the chipset claims 10Hz update rate, but after several mails with the manufacturer it seems that this 10Hz is useless since it's not available to the user. 1Hz updates is all that you can get.
It really borders on dishonest advertising, since this is one of the features that got me interested. I should have read the programming manual before I guess...

So... unless you're happy with 1Hz position fix updates for your UAV I would avoid SiRF based modules.

[Arp]

I am leaning on getting the new FMA copilot 8 ...
I would advise to consider carefully -- since to my knowledge, CP4 and CP8 have a significant difference.

To my knowledge, CP8 was integrated with a radio receiver, while CP4 expected input from a separate receiver (or a servo controller). As such, they would be suitable for different applications.

[danstrider]

The data sheet for the chipset claims 10Hz update rate, but after several mails with the manufacturer it seems that this 10Hz is useless since it's not available to the user. 1Hz updates is all that you can get.
It really borders on dishonest advertising, since this is one of the features that got me interested.

Wow, that's rotten. Sorry it didn't work out, though it doesn't look like it was your fault by any means.



If you're still looking for better than 1Hz, the U-Blox (www.u-blox.com) SAM-LS and TIM modules can run at 4Hz. *I haven't yet configured mine to do this b/c I'm still working on the logging software, but I have read about others who have been successful.

Dan