Replies to This Discussion

ModeratorPermalink Reply by Sgt Ric on July 21, 2010 at 10:07am

I wasn't sure, -thats why I asked for clarification, since each has it's own requirements and complications.

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Permalink Reply by Boz on July 19, 2010 at 9:58am

I tried the wifi link and its both good and bad.

The good:

it's cheap and easy to make it work - and it does work. the quality is better than analog, too, noise free.. and latency is not bad.. but..

The bad:
It's not all that long distance and if you lose the wifi link, it takes long enough to re-establish that you have already crashed. I barely go more than 500m by security, even if it could go much further, it doesn't feel safe enough. At this short range no issue however.

It lose link a bit "at random" (it feels like using a Spektrum radio for FPV, except Spektrums reconnect quick, if you have Spektrum+FPV or UAV experience you'll know what I mean)

Also, the power ratings and sensitivity ratings of the wifi devices aren't any better than cheap analog ones. That means, a 1W rated Alfa device does not emit at 1W. It's approx 800-900mW in 802.11b at 1Mbit (which is not enough) and around 4-500mW at 54Mbit, 802.11g (it's not bad at all but it's not what it says)

Likewise, I have found out the sensitivity at 54Mbit to be around -60dbm (its -76bdm rated or so I think so it's a pretty good drop..) - keep in mind its one of the best consumer wifi device (there are better ones but they cost a lot more). You can fix the power issue with a booster, but not the sensitivity.

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Permalink Reply by Andre S on July 21, 2010 at 9:24am

I have had similar experiences w.r.t "random" link losses. I used ad-hoc mode and was somewhat surprised that the wifi card would not even send out a packet if there there was not other node in the same cell (although this may be specific to the driver/card.. no idea). At least the LED on the stick stopped flashing once I seemed to have lost the link during my tests on the ground.. This was for UDP broadcast packets.

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Permalink Reply by Jeremy on July 21, 2010 at 10:14am

patch the drivers your using and use the link on a linux box most of these issues will disapear. There are tons of driver patches for linux that solves these issues. I use a adhoc setup from my UAV to my GS mine goes from a gumstix over/ UDB combo setup I built. There is one alfa adapter to stream the connection to the GS, which initially had a patched driver for the wifi card but is now running my own driver which tuned out the last few issues I was having and I am getting roughly 50mbps average streaming rate. I also have another wifi card onboard but it has nothing to do with a connection back to the GS. Hope this helps some, if your running on a linux box and interested I can clean up my driver and post it in a little while. but the driver I made is very specific and built for an arm platform so not sure would easily work on i86 without some retweaking

Also you should be running a script to look for a loss of connection and making it auto reconnect if you loose it. I have had luck with up to roughly 2 miles ( the furthest I have flown my UDB at this point, no signs of loosing connection for me yet) with just a patch antenna on the groung and a 9bi duck on the plane

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Permalink Reply by Andre S on July 21, 2010 at 10:36am

Thanks for the optimistic news :)

Both the macbook on the ground and the gumstix overo in my setup run linux (macbook relatively recent Ubuntu with updated kernel). However, I had a headache to get one of the wifi adapters working at all and needed to use a driver from the staging branch of the kernel (IIRC), which are supposedly experimental. Both adapters are based on Ralink chips, though I right now don't remember which ones.

I would definitely be interested in as much detail was possible.. like which wifi cards you use and which drivers and whatnot. Why did you for example need to modify the driver? To get it run on the overo ARM? Thanks for your patience :)

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Permalink Reply by Jeremy on July 21, 2010 at 10:47am

I am using an overo fire, it has an onboard wifi chipset marvel sdio, this one does not connect to the GS, its job is different. The one I connect to the GS is a USB alfa adapter. The onboard chip I had to use a driver for the same chipset but from the OLPC project as it gives more functionality to the onboard system. If you look up OLPC firmware you will find the drivers, but its VERY tricky to get it working for gumstix. For the alfa the reason I had to patch the drivers and then further tweak it was to give me the full functionality of what I am trying to do with my system. with the stock driver for the alfa there were dropping and distance issues as it was not giving me full control of the chip in the adapter, So I patched that driver as I normally would for giving it full abilities for my security uses, which drastically improved performance but still was not giving me the bandwidth I wanted so I further tweaked it with the help of a wifi driver guru thats in my lab. The final mods where to make it function cleaner on the gumstix arm setup and some of the bandwidth issues it was having was because of it being on an arm. I tried the same driver on just my i86 linux box and it wouldnt even modprob.

If you post the exact chips your using I can point you to what I would use for a starting driver patch and see where it takes you. Just a hint though most of the patches you want are also the same patches you find for doing security audits :) Feel free to IM me if you want me to email you the driver I have on the gumstix, I would be happy to trade a bunch of the gumstix tweaks I have done, especially if your a bitbake recipe master as I am lost in a few recipes I am making :P Of course I will share even if your not but worth throwing it out there as I am tired of natively compiling some programs on the gumstix.

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Permalink Reply by Mike W on July 21, 2010 at 11:19am

Has anyone tried boosting power on a Linksys WRT54GL after flashing the firmware with DD-WRT or OpenWRT?
I own a few 54GL's (awesome routers by the way) and the first thing I do is flash the firmware with DD-WRT. The additional functionality is priceless. They can be field striped very easily to just the main board and two antennas and the weight is only a few ounces. They also host a serial port on the board that you can solder headers to. I've read a couple accounts of people using them as the sole control and communications platform for remote control applications (usually ground vehicles), but since they run at ~250 Mhz and there is ~MB of free memory on board, and its capable of easily connecting to an SD card, you can really expand them to do a lot!

I really have to get of my WRT54GL's with the power boosted way up (again done in firmware) flying and let you know what the results are.

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Permalink Reply by Jeremy on July 21, 2010 at 11:26am

That seems like an awfully big footprint to use in a plane though. Those boards are not that small, even though they dont weigh much. Just my opinion. With my gumstix I still have yet to pass 35% cpu usage and its streaming video sending data to the GS and tracking antenna and running any where from 10-30 scripts and programs at any given time. plus I have 120 GB thumb drive and a 16gb sdcard (for the OS) plus the onboard nand. all running at 700mhz. be careful boosting your tx power on your chipset, once you pass a certain point its easy to fry those chips, especially depending on the driver patches you use. :) Just my .02. I have 35 flights running my setup so far with no issues with distance or drop outs.

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Permalink Reply by Mike W on July 21, 2010 at 11:37am

Wow thats fantastic! And yes your right about boosting the power and frying the chips, I've read about people bricking them online.

Will you be posting a build log of your Overo Fire anytime soon? I bought one of those boards a few months ago but I havn't gotten around to playing with it much yet. Also what range are you getting?

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ModeratorPermalink Reply by Sgt Ric on July 21, 2010 at 12:23pm

Check with TJ Bordelon (one of our members).
I know he has been working with wifi for dozens of years now.

Check out his site.

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ModeratorPermalink Reply by Morli on July 21, 2010 at 12:27pm

6 hour ride sucks but gives you lot of private time to write about :), so please post as much details as possible of "what to & what not to" with lots of photos+ some videos. You can start a new blog for it.I think there is fair enough amount of interest for Overo + autopilots here. thanks

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Permalink Reply by Boz on July 21, 2010 at 3:05pm

Jeremy,
I take it you are not really using wifi (802.11), only the chipset right?

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