I decided to pick up one of those RCTimer APM boards a few weeks ago to help support free trade. This was before 3dR lowered the cost of the APM board. The kit complete comes with their clone of the APM, Radio Modem, and GPS. The kit arrived and I noticed many things are alike. Including the silk screening on the back of the radio modem that says "3d Robotics" that was covered up by the RCTimer sticker. Then again some items are different. One of which is the plug they give you for the radio modem. 

3d Robotics provides the opposite plugging of what RCTimer provides here. This creates a slight problem if you don't have a cable to swap things around. Thinking about the issue I recalled seeing UART silk screened on the bottom of the board. Flipping it over I noticed that UART 0 is labeled on one side.


Sure enough it's labeled UART0 just like the 3dR port you'd normally plug a radio modem into. After moving the wires around in the plug decided to give it a whirl and it works.

Thinking about it I realized something. Does this mean I can plug my regular 3dR modem into the normal UART0/2 port.. Then plug the Mini mOSD into the UART0 TX port on the side? Many folks talk about making a Y-Cable to attach the Mini mOSD AND Telemetry modems. Seems like adding a pin header on the other side and attaching there is cleaner. 


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  • Okay, here is what i would like to do and am going to try.


    I have the :




    4)3DR Telemetry

    5)LEDs later on.

    I am going to hook this all up by having the 3DR Telem connected to the APM on the appropiate spot.

    Have the IOBoard and the MavLinkOSD connected to UART0 like it was a Y-Cable

    and then utilize a relay on the IOBoard to turn the power on and off for the 3DR Telemtry.

    Reason:  If I am flying in FPV then i don't want the 3DR Rado On, I am just wondering if it would be a problem to Turn the power on and off for the Telem Radio.  This would be on the ground of course... never in flight so would that affect anything.  Like sequence of components to be on.  

    I am also going to use the IO Board to send Telem to the Radio via the Frysky option on D5 and D6.

    Comments, suggestions?

    Thanks in advance, 


  • Great post gentlemen, my RCT OSD, APM2.5 and Telem components came with DF13 4 pin to DF13 5 pin wires and the Servo Type wires as well.  I can use the DF13 4 pin to DF13 5 pin plug from the Telem to the APM2.5 directly.  Then the 4 pin to 4 pin servo type wire from the OSD to the APM2.5.  The one problem is the 4 pin to 4 pin servo type wire has Gnd/Vc/Rx/Tx, so I just cut the wire and switched them around to give me Rx/Tx/Vc/Gnd for the APM2.5 side.  I will add pictures shortly.

  • Yes it works fine. When you make the Y cable you're essentially doing the same thing. I did notice with the RC Timer telemetry if I plug it in to UART0 I can't use the USB port. If I plug it into UART0/2 then I can use the USB Port and telemetry. That's why I flipped things around and placed the MinimOSD on UART0. When the OSD is being used along with telemetry the OSD is a receive only device. 

  • @Scott - So you have the 3DR ratio on the UART0/2 plug the (DF13 one) and MinimOSD on the UART0 pins on the other side? Does everything work ok like this? I was under the impression that you could only use one or the other port but not both.

    I am only using UART0 as I was an early adpoter of APM2.5 and they were not shipping with the newer DF13 telem cable at that point. However, if it works with both ports, I'll keep that in mind for future upgrades!

  • From my understanding. The minimOSD sends a command to the APM to tell it to start sending MAVLINK data. If you're running telemetry + minimOSD then the telemetry does this for you. 


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  • how come the official docs don't say this? seems to be the perfect way to have both modem and OSD! I just soldered on 3 pins and used a servo cable.

  • Ok here's how I ended up hooking this up in the long run. Sadly RCT only includes a DF13 4 pin to DF13 5 pin plug in their whole kit. If you order the telemetry after market you get a cable that doesn't work. Ended up getting a DF13 4 pin to 4 pin cable and the extra DF13 5 pin housing..


  • I just seen the RCTimer offer for AMP2.5 clone (433Mhz ArduFlyer UAV GPS Flight Control System) (The Clone War has started)
    I think that the connection of 3DR modem and APM2.5 showed in RCTimer page is the same that we do within 3DR modem and APM2 (it is that I have done, and works).

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