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Nov 15, 2013, 10:55 PM
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RFU Install Question


Well I have my RFUs and I'm about to install one on my QAV500, but I have a couple questions.

Please refer to THIS POST for a visual reference if you need to. The quad has evolved some since those photos were taken, but the airframe is the same. I'm now using an OpenPilot Revolution controller and there's currently no GPS receiver on it, but that's a feature I plan to add when the OP GPS becomes available again (December?). It also has carbon fiber props on it now.

Per the discussion in posts #31 & #32 of the same thread my plan is to mount the RFU's antennas sticking out of the top and bottom of the airframe (under & over the battery pack) angled rearwards at 45. That will put the bottom antenna very near (if not in contact with) the ground when the quad is on the ground, but I assume that will be OK considering the antenna diversity and the fact that the top antenna will be free and clear of the ground. Also, I doubt my TX and I will ever be more that 30' or so from the quad when it's on the ground unless I have one of those "oops" events.

The way I'd like to mount them is to build a pair of mounting blocks with a piece of semi-rigid plastic pushrod sleeve stuck in each one, mount them to the airframe, and slide the antenna wires into the sleeves. I'm guessing that the plastic sleeve will be transparent to the 2.4GHz signal, but I'd like some verification. I could extend the white tips of the antenna wires beyond the sleeve, but I'd prefer to let the sleeves protect the tips and keep them straight if there's no problem doing that.

Comments?

Also, any suggestions for a practical way to range-test an RX on a multirotor? They don't have control surfaces to watch and it's next to impossible to see/hear the motors spinning from the recommended distance.

Thanks!

Pete
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Nov 15, 2013, 11:57 PM
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I have range checked using a flag mounted on an extra servo Y-corded in to the rudder channel. No reason to use the rudder channel except that has been the channel I always used. In the "good old days" the shorted range was always with the transmitter antenna pointed at the model with the receiver antenna shielded by the engine.
Nov 16, 2013, 12:32 AM
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Good idea, Chuck, but there are no discrete channel outputs on the RFU. I use PPM mode when I connect Nanos to my multirotor controllers, so I don't have discrete channel outputs from them either. I suppose I could get a Channel Expander and hook it up just for range testing, but then I wouldn't be range-testing the configuration I'd actually be flying.

Pete
Nov 16, 2013, 04:09 PM
Pete, do you have lights on that thing? My multirotors have flashing lights in auto-stabilization mode. I just look at the lights and flip the switch back and forth to see if it changes instantly.
Nov 16, 2013, 07:33 PM
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The controller board has an LED on it but it's tiny (nothing like the LED on a DJI Naza). In retrospect, I think I have an answer... I can use the audio channel of my video link to listen to the motors during a range test. I could even watch the motors spin or watch LEDs on the controller or RFU, but I think it will be tough to walk around without tripping over and walking into stuff with the goggles on.

I'm a lot more interested in what you think of my antenna mounting plan, though. In particular I'd like to know whether it's OK to have the active ends of the antenna wires inside pieces of plastic tubing.

Pete
Nov 16, 2013, 07:51 PM
If you have a video/audio transmitter on that thing, range check the heck out of it! No matter what frequency you are using, the range will be reduced.
Nov 17, 2013, 07:10 PM
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Jim ...


To do this the way I had in mind I'm going to have to run the black shielded part of the bottom antenna wire right between two ESCs and the transition from shielded to unshielded will only be 2-3 inches away from them. Conventional wisdom says this isn't a good idea which means I won't be able to have an antenna wire pointing down from the bottom of my quad, but before I abandon the idea I'd like to hear your opinion.

Second question: How much does a spinning carbon fiber prop affect signal integrity if the prop circle is shadowing the RX antenna?

Pete
Nov 17, 2013, 09:20 PM
The white tip of the antenna wire is the actual antenna. You shouldn't really have an issue running the coax itself next to noisey things. The black coax has a sold mesh ground shielding under it, with a layer of plastic isolating the center wire, which is the actual antenna portion.

Spinning carbon can act like a wall if it is spinning in front of the antenna. In multi-rotor setups, you are always want the receiver under the props (providing you are not flipping it, in which case you need to pay real close attention to installation around spinning carbon at various angles).


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