Dear Customer,

You are receiving this notice because our records indicate that you purchased an airspeed sensor from 3D Robotics. Our ongoing product testing has turned up a rarely occurring issue that can cause poor performance of the airspeed sensor.

There is no further action required if:

You are not using an airspeed sensor with APM 2.5
You are using an APM 1.0 or APM 2.0

When using the APM 2.5 with a telemetry radio and GPS, the current draw of these two devices may cause inaccurate airspeed sensor readings. An immediate fix for this is to disable the airspeed sensor in the Mission Planner.

For those who do need to use the airspeed sensor along with GPS and telemetry radio, and are affected by this issue, you can return your APM 2.5 to us so that we may replace a single component on your board and remedy this issue entirely.

We will do this at no cost to you. Simply reply to this message, and we will issue you a return merchandise authorization (RMA) with instructions on shipping your APM 2.5 back to us.

We apologize for any inconvenience this may have caused you and look forward to continuing to provide you with the best quality autonomous products at the most affordable prices.

The 3DR Team

if the problem is real is what it is and how to fix it yourself?

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Replies to This Discussion


Jyothy Nagol.

Check for what?

i think i also lost an aircraft becasue of this. i had RD900 telemetry + Radio Rx and OSD and airspeed sensor + GPS. all powered by APM2.5. i lost it on June 29. now i know it.

@craig. who would pay the return shipping cahrges. i am located overseas

It doesn't involve overloading a fuse or any kind of brownout or safety issue. Higher current across that fuse just causes a drop in the reference voltage that can throw off readings on certain analog sensors, with the main one being the airspeed sensor. Other sensors are not affected enough to notice. 

3DR. Just contact 3DR and get an RMA.

It's unlikely you would loose an aircraft as a result of the noise but you should not be powering the RFD900 from the APM.  If you are transmitting at full power the radio requires more current than the APM can supply.

I received this notice too and I do use all the mentioned peripherals as well as a MinimOSD. My question is if there is any risk to not replacing the fuse other than some unreliable readings from the airspeed sensor. What might I expect to see as a result of this issue, an airspeed reading that fluctuates more than normal?


Nathaniel ~KD2DEY

I posted a bit of background info on drones-discuss, which may help explain where this change is coming from

      I can't help you with the components, but I can give you a bit of
      background that may help you decide if you need the change.

      The problem was first noticed when users were running relatively
      powerful telemetry radios off their telemetry port. For example, if you
      run a RFD900 radio at full power (30dBm), it will draw 900mA when
      transmitting, then almost zero a moment later. That ramp up and down of
      the power demand on the 3DR power brick through that fuse could cause
      the voltage on the AVR2560 MCU to vary by far more than it should. That
      led to the voltage reference on the airspeed port changing rapidly,
      which led to noisy airspeed results and in extreme cases could have
      taken the AVR2560 voltage below its safe level.

      Apart from the fix 3DR offers there are other ways you can avoid the
      problem. First off, you can monitor the HWSTATUS Vcc board voltage in
      your ground station (eg. MissionPlanner) and see if it is in fact
      varying significantly when on battery power with a telemetry radio. If
      its not varying much (eg. 0.1V or so) then you don't have a problem.

      If it is varying then you have some other options:

       1) turn down the power on your telemetry radio. You may not need all
          the power its drawing depending on the range you need

       2) power the radio externally. For example, the RFD900 has a jumper for
          external power. You can do the same on a 3DR radio with a bit of
          connector soldering.

      I should also mention that recent code changes make the impact of this
      problem on airspeed much less than it was with the 2.72 ArduPlane
      firmware. We previously did voltage scaling against Vcc, which was not
      correct, as the sensor is ratiometric. That made the problem much worse
      than it should have been. In 2.73 the airspeed noise isn't as bad, and
      also drops rapidly at higher airspeeds. It's only really an issue at
      lower airspeeds (say under 9 m/s).

      I also wonder if a strategically placed capacitor would help? I'm not an
      electronics person, so I don't really know. Maybe someone else could

      Cheers, Tridge

Re: What might I expect to see as a result of this issue, an airspeed reading that fluctuates more than normal?

yes, exactly

Hi, I'm interested to read that I shouldn't be powering my RFD900 from the APM2.5 telemetry port. I've been doing that without problem, but only up to Tx power of 25 so far.

The instructions at don't mention the RFD900, but the old manual had a specific RFD900 page that I think just said follow the 3DR setup instructions.

Anyway, how should I power it? Or how high can I set the Tx power if I'm using the APM2.5 telemetry port for power?

@Alexey Kozin, I am having seriuoss problem with my airspeed data since i am using APM2.5 with RD900 and also powering the Radio control Rx. i need a ticket issued so that i can send the APM2.5 for fuse replacement of fuse back to san diego. i have written to support but still waiting for ticket. unless i get a ticket number i cannot mail the APM2.5. thanx ravi


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