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Confused about APM telemetry VS FrSky and FPV

Discussion in 'Beginners Drone Forum' started by Delta Star, Aug 13, 2013.

  1. Delta Star

    Delta Star Member

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    Posted by Delta Star, Aug 13, 2013 #1
    Okay, I have tried to figure this out, and just can't seem to find the answers.

    Are there two different kinds of telemetry? I am trying to build my Y6 around an APM board, and I understand you can get some telemetry through an Xbee/MAVlink arrangement directly to Mission Planner.

    I also see others without the APM getting telemetry through an additional screen attached to their radio. This requires a special board for the 9X, which for some reason I already bought.

    Range for the Xbee sounds terrible, but it's required for Mission Planner to follow along with the mission. Range for the FrSky can be better, but it can't be read by Mission Planner, which seems pointless.

    After all that, I still don't know if either of these telemetry systems actually transfer any kind of video. I don't think so, though... because I think the preferred method is to use a separate 5.8gz video transmitter/receiver.

    Lastly, does the go pro supply the video feed? Or do people generally just install a separate camera for FPV?
     
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  2. RTRyder

    RTRyder Merlin of Multirotors

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    Posted by RTRyder, Aug 14, 2013 #2
    The quick and easy summary is, the APM sends detailed data about flight controller status and location information from a GPS module over a radio link to the ground station for use with the GS software for flight planning and monitoring. FRSky sends basic information by two way communication over the 2.4 gHz band and is limited to data about the link between the transmitter and receiver unless additional hardware (sensors) are added on the receiver end to monitor those specific things.

    The APM telemetry is a lot more detailed since it's sending information about location as well as status of things related to the flight controller itself, with an RSSI connection to the receiver it can also send basic data about the strength of the signal from the transmitter. FRSky telemetry at it's most basic is only sending information about the link between the transmitter and receiver, it knows nothing about the flight controller or what it's doing. By adding sensors to the FRSky system you can get more than just radio link data, there are sensors for battery monitoring, altitude, speed, and a couple other things like fuel level for gas or nitro powered planes and helis, but it still cannot link to the flight controller or overlay that data onto a video signal.

    APM sends data that is intended for use with the ground station for waypoints or completely autonomous flight, by adding a Mavlink OSD you can capture some of that data to be displayed as an overlay on the video stream for FPV flight whether it be through goggles or by a monitor of some sort. FRSky on the other hand is limited to providing an RSSI link to either a flight controller such as the APM or to an independant OSD providing telemetry overlay for the FPV video stream and in order to do that you need specific receivers that have an RSSI out such as the DR8-XP.

    Video is a completely separate system and can be sent over a variety of different frequencies. The basic system takes a video signal from a camera and transmits it as a data stream to a receiver on the ground. In order to get the telemetry data from the flight controller or other onboard systems you need to pass the video signal through an OSD (On Screen Display) module which then adds that information as an overlay to the signal from the camera. As I mentioned above the APM data can be added to the video stream through a Mavlink OSD board, the FRSky data cannot, it can only be displayed on the data screen that is connected to the transmitter module with the exception of the RSSI information provided the receiver is capable of generating the RSSI data for the OSD.

    Some OSD systems are independant units that have GPS modules and battery/current monitors that can add that telemetry data to the video so the pilot can see things like altitude, speed, distance, direction, etc while flying FPV and may not have any links to the flight controller or receiver although most are capable of taking RSSI data from the receiver to display the signal strength as part of the telemetry data.

    Lastly, almost any camera that has live video out connections can be used to send video to the ground, flying the airvraft by video is usually done by either a dedicated FPV camera or through a GoPro video feed. While it is possible to use video from a camera like a Sony Nex 5, those video feeds often have to go through a high definition to analog convertor before they can be transmitted and that adds latency. The last thing you want is any significant lag between what the camera is seeing and when the pilot is seeing it, that's why most FPV pilots use a dedicated camera which is the lowest in overall latency with the GoPro being a close second.

    Ken
     
  3. Delta Star

    Delta Star Member

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    Posted by Delta Star, Aug 17, 2013 #3
    Thank you so much for the extensive response! Very informative :) I still have a couple unclear points though... 1) Is the Xbee's range inferior to that of the FrSky? Or is that just a matter of getting a better antenna set? Is there a high gain system I should be considering? 2) If I get the Xbee, I understand that sends telemetry over MAVlink. You said the OSD board can add an overlay to the video, but is the Xbee sending the video as well? Or am I then looking for a separate video tx system on top of my craft's 2.4 and the Xbee's 433 signals? In other words, do I then get a 5.8 just for the video? And if so, what's the best one to get?
     
  4. dazzab

    dazzab Member

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    Canberra Australia
    Posted by dazzab, Aug 17, 2013 #4
    Forget about the XBee. The 3DR TX/RX radio kit works much better and is cheap. You can get it in 900mhz or 2.4 versions depending on your need.
     
  5. Delta Star

    Delta Star Member

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    Posted by Delta Star, Aug 17, 2013 #5
    Forgotten. 3DR it is. Then let me rephrase all that :)...

    1) Is the 3DR tx's range inferior to that of the FrSky? Or is that just a matter of getting a better antenna set? Is there a high gain system I should be considering? 2) If I get the 3DR tx, I understand that sends telemetry over MAVlink. You said the OSD board can add an overlay to the video, but is the 3DR sending the video as well? Or am I then looking for a separate video tx system on top of my craft's 2.4 and the 3DR's 433 signals? In other words, do I then get a 5.8 just for the video? And if so, what's the best one to get?
     
  6. dazzab

    dazzab Member

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    Canberra Australia
    Posted by dazzab, Aug 17, 2013 #6
    Well, first of all, how far do you need it to go? That will determine what antennas you use etc. I can assure you it will go much further than LOS.

    As for the video, it's totally separate system. You can buy OSD boards from 3DR, JDrones etc that accept input from the 3DR radios and overlay all the flight info but that's the only interaction. How you send video from your copter is a separate exercise and requires a video TX on the copter and something on the ground to receive it like Googles with inbuilt Rx or a little monitor with built in Rx or even a small Rx with AV jacks that you can plug whatever you like in to them. I've only used one Tx so far and I think in comparison to what others here use it's a cheapy so hopefully others will chime in here on what video Tx they use. I'm using the Boscam 5.8Ghz 500mW AV Tx which you can get from HobbyKing. Here in Australia 5.8Ghz is legal but I think the max legal power is actually 50mW so apparently I'm a criminal broadcaster.
     
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