Replies to This Discussion

DeveloperPermalink Reply by R_Lefebvre on January 16, 2012 at 2:40pm

I believe the idea of getting the GPS out from under the blades... it's a hunch, but I don't think it's been proven one way or the other.  The idea is that carbon fiber conducts electricity, and blocks radio signals.  GPS signals are quite weak, and any disturbance can make them inaccurate.  So it's best to get the GPS up out from under the blade disk.

Maybe it's unnecessary, I don't think we really know yet.

I originally made my GPS mount under my blades, but I never found out if it made a difference.

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Permalink Reply by Alex O. on January 16, 2012 at 4:33pm

Thanks Robert I cannot prove it but my feelings are that it won't make any bit of difference because of the fact that many others used it successfully...

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Permalink Reply by malcolm churn on January 16, 2012 at 4:52pm

Hi Alex, that was a lot of reading...

Moving the gps from under the blades stops GPS Multipathing. I agree with you that it shouldn't cause an issue, but we are trying to get rid of any errors that may occur from hardware. 

Have a quick read of the following site.

http://gpsinformation.net/multipath.htm

Great that you are going to get involved. :)

APM and ACM are the same thing. I think we have settled on APM (ardupilot mega) :) 

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Permalink Reply by Alex O. on January 16, 2012 at 8:14pm

Thanks Malcolm, I checked that link. Although I have done lots of readings on GPS, I never came a cross with Multipath error. It was an interesting article. The question is that how the other commercial autopilot companies got away with it.

There are different grade GPS receivers out there but I bet that the GPS receivers used in those expensive commercial units are not any different than the ones Ardu pilot is using. I believe they are all 10hz receivers... 

You guys are doing many tests. Is it not possible to test this on the bench? The system can log all the sensor output signals so it should be easy to see I would think. GPS receiver can be covered with a carbon plate to simulate the blockage.

Just throwing an idea. Obviously you guys know this better...

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Permalink Reply by malcolm churn on January 17, 2012 at 1:47am

Like i said before, i don't think it makes any difference either, when the helicopter is on the table in my flat/apartment and i have it hooked up to the lap top with MP running it is bang on the mark in google earth. But i just wanted to make sure that it can get the best signal, electric helicopters are very smooth in operation but there is a lot of electrical and mechanical noise, it just made a bit more sense to do it that way.

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Permalink Reply by Alex O. on January 17, 2012 at 5:49am

Understood. I am glad we both think the same way...

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DeveloperPermalink Reply by Mark Colwell on January 17, 2012 at 6:04am

i have a bench test setup with Remzibi OSD reporting hdop readings.

Best hdop values is about 88,  under 100 is an excellent 3D fix.

Using 2 sets of 600 SAB carbon blades, I passed over GPS, and held then there for several minutes,

hdop would go up only a little to 96 highest value seen was 148,

Satellite count went from max of 10 down to 7, mostly at 9.

I tested this when GPS reception was very good, hdop was below 100 for 20 minutes.

Tested performed with a Ublox inside the house with a lot of RF from radios and videos Tx systems and several computers.

I can't get MTK to report hdop but, I believe it will perform almost as well as Ublox.

I think brownouts, EMI, and excessive vibration are the most likely cause of these issues.

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Permalink Reply by malcolm churn on January 17, 2012 at 7:19am

Thanks for the test info mark :) i used to have my gps fixed to the rear servo, but at the time i was having all sorts of issues with Loiter control, so i thought i would move it to the tail, to give the best possible GPS lock. But to be honest i don't think it made any difference.

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DeveloperPermalink Reply by Randy on January 17, 2012 at 7:21am

One nice thing about the blades not causing problems is we wouldn't need a super long gps cable!  Maybe I'll make a new 3d printed mount that puts it around the base of the tail...

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DeveloperPermalink Reply by Randy on January 17, 2012 at 7:19am

great to see this kind of testing.  It would be good if someone could give a try outside with engines running and not running.  I'd never heard of hdop before but seems like that really is a great way to estimate accuracy.

I tested over a year ago and found it difficult to get a good lock with the gps under the blades but I did have other problems back then too like a noisy power supply.

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Permalink Reply by malcolm churn on January 18, 2012 at 1:56am

I tested GPS last night indooors, had a lock of 8 sats and in MP the map was right over where i live. it didnt bounce or jump was solid for an hour. so maybe its ok to put it under the blades. 

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Permalink Reply by malcolm churn on January 18, 2012 at 1:53am

Dont know if any of you guys can help me with this.

Was using HIL with aerosim, on sunday night it was working really well, i updated MP to the latest version and tried again last night. Problem is it connects when i select the plugin, then after a few seconds drops out, the red LED stops flashing and the green one stays on. I can get it to reconnect if i hit alt tab to select MP window behind Aerosim,  but then the sticks have a huge delay. I followed the HIL sim on the wiki and like i say it worked fine on sunday night. i have now updated the software in the APM to the latest version in MP (HIL), but it does the same. i wonder if i'm missing something. All the baud rates are set correctly. i even reinstalled MP to the last version when it worked, and did the same with aerosim.

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