Powering The RFD900

RFD900 I know this isnt a 3dr product but i’m curious if anyone is using this telemetry link?

From what I hear it’s wise to power it from a 5V BEC otherwise I could brown out the Pixhawk. When I power it from a 5V BEC I find that I have to unplug then replug to get it to power on correctly. Looking on rfdesign.com.au/index.php/rfd900 website it does somewhat explain how to power the RFD900 from a separate 5V source “see below” it seems very vague instructions. I tried with and without the jumper, powering it off pins 2 and 4. connecting the ground wire to the BECs ground. Everything I try seems to be the same results unplug then replug to get connection.

Am I over thinking this?

The following cable from FTDI is compatible with the RFD900 modem. Pin 1 of the FTDI cable connects to Pin 1 of the RFD900 header.
ftdichip.com/Support/Documen … CABLES.pdf
To power the modem from the +5V USB power, a jumper is needed between pins 4 and 6.
To power the modem from an external +5V supply, connect power to pins 2 and 4 as shown above.

if you are using a current/voltage sensor with bec to power your Pixhawk then make sure there is a common ground between pin 2 “gnd on the rfd900” and gnd on the serial port of the Pixhawk and pin 4 would go to the other bec for power

see my dodgy mspaintjob for what i mean

Thank you for your quick response.

I tried that same configuration and still didn’t work unless i unplug and plug it back in.

Will the RFD900 pull to much power from the Pixhawk? I have been using it so long with the APM2,5 with no issues but the helicopters that I am flying today are a little pricey so I would hate for something to happen.

I’m no expert but here’s my thoughts. As far as unplug / replug to get it to connect [ solid green ] and transmit the data [ once in a great while I’ve had them, or other telem radios, go solid green but not transmits data] I have had that issue but very infrequently. If it’s not a huge headache getting it out of your model it might be worth taking the radios out and connect them direct to your pc one at a time and make certain the settings are the same for both. I know you can do this without a direct connect and do this via the telemetry but I know for certain once in a great while I could do that several times without it working but then did it direct via the cable to the pc and then it worked fine. You might also want to make sure the LBT box is not checked.

As far a separate power source I was considering that myself until I did a little testing as to just how much the RDF radio uses. I seriously could barely tell the difference in remaining voltage on the battery after a 10 minute flight with the radio and a 10 minute flight without. It seemed if I was concerned about a brown out I would be far better off concerning myself with making sure I flew 10 minutes not 11. Also as far as backup redundancy on power the pixhawk can be set up that way without the need to power the RFD separate manually so to speak. For instance in my gas model [ which is the model I’d be more concerned about the issue because the flight time is 40 minutes ] I have the power module feeding the pixhawk AND a separately switched 5V feeding the servo out rail on the pixhawk. If the main lipo feeding the pixhawk via the power module goes low [ the one feeding the RFD as well ] it automatically switches and uses power from the servo rail with no loss of control to the model. Thanks 3DR! :] That is one of the great benefits of the pixhawk although the older apm’s can effectively have two power sources too via that jumper. But… it cannot automatically switch to the second source. If one goes dead your done irregardless of what the power is on the other one.

Another thought is what is the power setting on your radio? When I did the testing I mentioned it was on full power [ 30 ] and even with that it was not a big issue. They are commonly flown with 1/2 the max setting without issue.

I could be full of boloney on some of that maybe somebody else can chime in but that’s what I came up with. Good luck!