Hello, I'm looking for a little help / guidance with wireless telemetry.
I would like to add the wireless telemetry to my APM to use with the GCS, as I live in the UK I can't use the Xbee 900's as this is the band used by the mobile telephones here. I have a 2.4 Ghz Futaba T7C so I can't use the 2.4 Ghz Xbee's either. My thoughts are to end up using a 5.8 Ghz video link 2.4 Ghz radio and I hope the 433 Mhz telemetry.
I have seen this post in the Arducopter section of the DIY drones site, there is talk of using a 433 Mhz link, which I understand will work using these Wireless 1 & Wireless 2 it looks like one for the connection to a PC and the other for the APM. I have also seen other posts talking about these as an option on the forum but none of the postings answer the following question / concern:
Reading all the posts it would appear as if it is not to complicated, however as I don't have a great deal of programming experience or a massive background in electronics would I be opening a can 'o' worms which I could not deal with by going forward with this? Could you point me towards a set of instructions to make this work?
I hope someone(s) will be able to help me with this.
Hi Johann, I'm looking at the these now, it seems that the issues with the 868 Xbee's is the “10% duty cycle” that James spoke about a little earlier, from my readings on the web this morning, it looks as if the issue is with the “ETSI” settings. My understanding of the ETSI is that it will only allow (10%) 6 min's transmission in any 60 min's period before it will stop transmitting, then will start up again. This makes it useless for data streaming in the first instance. This is the number one complaint about using the 868 for telemetry.
There is some more information here on ways to over come the issue with the ETSI.
It seems as if the ETSI can not be changed, but the units can be reset so a work around if you will, a simple cycle of the power seems to fix the issues, so the unit is reset and then can go on about its business for another 6 min's.
HI Martint, Yes the duty cycle can be got around by simply applying a low signal on the reset pin. The signal only needs to be very short and the units connect again straight away. The 10% duty cycle is fixed an cannot be changed but please bear in mind it's purely dependent on how much data your pushing through and at what rate. In my case I use 9600 bps and get around 40 mins before it needs a reset but since my lipo only gives about 30 mins max I have not even bothered putting any resetting circuit on the airframe and have flown my plane all summer on nothing but the 868. I'm also using mine for servo control from a joystick so it was critical the units didn't lock. The 6 Mins I presume is using the maximum data rate with a constant stream of data. Even this was your requirement using a simple external circuit to reset the unit every 5 mins or so would solve it. The 10% duty cycle seems like it would cripple the usefulness of such a device but to be honest I found it wasn't too bad and given that we have limited options here in the uk regarding good kit it seemed the best of a bad bunch.
HI D, Johann
I Have'nt really let it go too far out of LOS because I need to alter the GCS software to change the power levels depending on the range and I havent got round to it yet. If they are set too high at short distances they don't work properly because its like they are shouting at each other. Even so, the lowest power level of 1mw seems to go beyond the distance of my Spektrum gear with the right antenna. The GCS I was am using works just fine at 9600.
I bought mine from Digiuk I think. They had a special offer on for the evaluation kit which contained everything to get you going. I then just bought a small generic xbee breakout board for the plane.
Johann, it looks as if the quest for telemetry is nearing its end, we have made a few twist and turns arriving at this point, however I have a good feeling now that there is a firm direction to head in!
Now I guess it is time to source the boards and other items at a good price and time frame.
It looks like as if there might be other interested parties in joining in with the Xbee 868 quest for telemetry, as a thought, we may get the Xbee's for a better price if we were to order a few units at the same time from one supplier, what are the thoughts of the those who have been adding there thoughts, and those who may have been lurking to gain the information before deciding to buy like Davey.
I did come across a very good page on the web while looking into the 868’s which had a lot of information and a very long flight log, I have uploaded the log for others to look at with the thoughts of aspirations of what we could be able to acheieve using these Xbee’s.
James, thank you for your time and information, I think you have helped a lot of people with the postings you have made here!
I had a high level of confidence that we (the community) would make our way to the bottom of the telemetry issues using Xbee’s however, the duty cycle did look like it was going to cause an issue without some help.
your welcome Martint. I went through the same problems with telemetry at the start of last year so its great to be able to share a bit of experience and save someone else the hassle. There was also a discussion started by reto back in jan 2009 called "Xbee Pro long range made affordable until end of February 2009" in which we played with these modules quite a bit so there is some good advice on there should you decide to go with the modules.
I will be looking to get the 868's ASAP! I have seen a kit here in the UK for £99+Vat + Delivery. I believe from your post before that the kit is the same as you got. I would like to see if I can nail the price down with a group buy if others are interested :)
One question I forgot to ask you, did you just follow the manual in the APM page to get the units up and running in the end?
HI Martint, Not really as they can just run straight out of the box. I used the utility to set the baud rate and power I wanted. There was also an option to turn off repeatng of missed packets. I can't recall at the moment exactly what it was called but it's in that post and goes towards keeping your duty cycle down so it's worth doing (you don't want to re-transmit data which has become out of date). Thanks for that link. It is the same kit and I need a another one for a skywalker I have just bought and I cant find my original site were i got mine. it's actually works out cheaper getting the kit than buying them separate.
I also have one of the Xtreembee boards, however they will only go up to 0.3A and the Xbee pro 868's will need 0.8A if you are looking to ramp them up for max range. So these might be redundant. I have read that you do not need to run them at max power, however it is worthwhile noting the limit of the Xtreembee boards.
I thought that the deal on the package was good, but I hope to make it better if we have a few people that would like the units, I think they are based in the South East of England, so they will be under some snow at the moment, orders will take a while to come through even if placed today with the Christmas post & snow. When are you heading back home?
I also think that the kits do not come with the antennas, so you may / may not need them?