Distributor Comment by Martint BuildYourOwnDrone.co.uk on April 6, 2012 at 4:05pm

Hi Tridge,

 

Thank you for the swift reply, I'm not a radio expert, that's why I have so many questions!

 

I see the allocation in the 433 band, however is the 10% cycle only 6 min's of use in every 60 min's?, so will there be the 54 min's of down time where the radios will be silent like the duty cycle on the 868 xbees I blogged about, about a year or so back. Do you know if the 10 Mw going to give us the range of Km's? On the Xbees there is only a very short range when they are at 10Mw's......

 

The other question I had with the use here in the UK and in the EU is due to the Repeater Output Channels here, they operate in the 432.994 - 433.381MHz range, how will this work with the 3DR radios?

I wish they would let us use 900 Mhz here.... life would be so much easier!

 

Regards

 

Martin.

Comment by Grips on April 6, 2012 at 4:36pm

A note for Canadian Users: According to Industry Canada policy, you cannot import any radio device which is not approved by them. At this time, these radios are not approved to be used in Canada, by Industry Canada and will not be going through the certification process. Please check out the Industry Canada documentation found on their website to make sure your butt is covered.

Perhaps we could get together and see how much the certification could cost. The Xbee's are certified by Industry Canada for use in Canada. To use either of the above radios legally, you still require an amateur radio operators certificate to use the frequencies utilized.

Comment by Keith S on April 6, 2012 at 5:20pm

Anybody know if there is a reason to upgrade yet. I looked through the documentation and don't see why to upgrade. 156k to 250k and frequency hopping are two that pop out compared to the xbee's. Did I miss something?

3D Robotics Comment by Chris Anderson on April 6, 2012 at 5:39pm

Keith: There's no particular need to upgrade, but if you've been frustrated by Xbees "bricking" (an all-too-common occurance), you'll be pleased to know that they don't do that. They also have less packet loss and are easier to set up. But if your Xbees are working well for you, you might as well stick with them. 

Developer Comment by Andrew Tridgell on April 6, 2012 at 5:43pm

@Martin,

A 10% duty cycle is not nearly as bad as it sounds. I've tested these radios with a 10% duty cycle with AIR_SPEED=128 and ECC=1 and I can get continuous telemetry of all streams from APM at 2Hz.

The reason this works is that it doesn't just transmit continuously for 6 minutes then shutdown. The 'duty cycle' is calculated based on how many microseconds the transmitter is active in each TDM round. The normal duty cycle for an APM sending telemetry is only about 30% for typical Mission Planner settings, so 10% just means that your maximum telemetry stream rate is a bit lower.

So you can run with a duty cycle of 10% all day, and you will keep a good link to your APM. Your GPS data points will be a bit further apart, but it is quite usable.

Cheers, Tridge

Developer Comment by Andrew Tridgell on April 6, 2012 at 5:47pm

@Keith,

The new radios should perform better than Xbees because we have been able to build features into the radio firmware that we could never do with an Xbee. For example, the 3DR radio sends information to the APM telling it the state of the internal serial buffers and signal strengths. That allows the APM to modify its telemetry rates to ensure that you don't get serial overruns. That makes a big difference in terms of reliability.

The 3DR radios are also a lot more customisable. You can drop the air speed right down for very long range and you can enable MAVLink framing which optimises the packet layout to match the telemetry format that APM uses.

So I'm expecting that people will find these radios do a lot better than Xbees.

Cheers, Tridge

Comment by Jonathan M on April 6, 2012 at 5:48pm

Pretty cool!  I am glad I waited :)

Unfortunately, I just got a 900mhz 1W FPV system from my friend.  Any chance they I can get enough frequency separation between the two transmitters?  My gut says not a chance

Developer Comment by Andrew Tridgell on April 6, 2012 at 5:57pm

@Jonathan,

yep, that shouldn't be hard. If you are in the USA, you can use any freq from 902 to 928 MHz. At 64 kbps AIR_SPEED (which is the default), you'll need about 100kHz between channels, and to meet US regulations you need to use 50 channels. So, you can pick any 5MHz band or wider for the 3DR radios in that range. See the wiki page for how to set that up.

To prevent interference, just keep the FPV system a couple of hundred kHz from whatever range you set for the 3DR radios. The high level of configurability of the new radios is one of their big advantages.

Also, even if you can't adjust the frequency of the FPV system, you'll probably find it works OK even with the default settings. The frequency hopping in the 3DR radios means it is quite resistant to interference from other radios.

Cheers, Tridge

Comment by Rick Stewart on April 6, 2012 at 6:10pm

Wow, its like they waited till I pulled the trigger on the XBee and then they introduced this. :(  Oh well, Good work 3DR team, I cant wait to hear the reviews.  Cheers,

Rick

Comment by Keith S on April 6, 2012 at 6:43pm

Andrew Tridgell,

Alright, that's really great news! Having that kind of firmware flexability opens up some great possibilities.

Thanks for sharing....

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