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  1. #1
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    Telemetry Guide - making sense of all the Sensors and Expanders and stuff

    I thought I'd add a post on Telemetry and all the parts that could be used after having played with various configurations for a while.

    I find the documentation and guidance on Traxxas's website a bit lousy in this area. And I had to learn a bunch of stuff by trial and error. I have no doubt many people on these forums know the topic better than I do but I certainly would have appreciated this kind of content when I started out, so I hope this guide is useful for anyone who are getting into Telemetry.

    I may have some gaps and even errors in my understanding and I would appreciate any replies to correct me whenever necessary.

    I will link all part numbers used to Amazon, just because I think the information on amazon is more useful than the information on traxxas.com (where you normally only see a list of compatible models).

    So let's start.

    What is Telemetry? Think of telemetry as feedback from your model's receiver to you. Two-way communication. You send commands to the receiver (throttle, steering) but you may want the receiver to tell you stuff about itself. What is the motor RPM, what is the ESC temperature, what is the battery voltage. Traxxas implements telemetry brilliantly through use of the wireless link module and a phone app. So your phone becomes the screen on which you can get this information real-time while driving.

    Wireless Link Module
    To get the obvious out of the way, if you want to start with telemetry you have to purchase the Wireless Link Module (6511) which is easily installed in your receiver. If you have multiple models I'd recommend getting one for each transmitter. I'd also STRONGLY recommend you get Transmitter Phone Mount (6532) so that you can mount your phone on top the transmitter. The mount is great and can easily be unclipped from the transmitter so no need to get more than one of those.

    firmware updates! yay!
    ONE reason to get 6511 is just to do Firmware Updates on your model. The first time I connect Link to a model I normally have to do fw updates for the Receiver and the ESC and some other sub-systems. Which means that Traxxas is bringing out better firmware, and your model will not get patched unless you connect through the Link app. Firmware updates can be important, for example certain X-Maxx users report that the ESCs burst out in flames, and perhaps (I don't know but perhaps) Traxxas has since resolved this by tweaking some settings in firmware.

    So the first time you connect make sure your phone has enough battery to last a while and go through the firmware process.

    Standard Telemetry, without any Expanders...
    The standard receiver has a port called "V/T" and a port called "RPM". These are both 3-pin plugs (and that is important for later).

    Some of the more expensive traxxas models come with volt or temp or rpm sensors pre-installed, and if you have these you'll get some telemetry readings immediately after connecting. If you don't have anything plugged into these two ports, then you can purchase these sensors
    Temperature and Voltage Sensor, long (6521)
    Temperature and Voltage Sensor, short (6523)
    RPM Sensor, long (6520)
    RPM Sensor, short (6522)

    The T/V sensor (6521/6523) measures BOTH temp and voltage.

    The grey plug goes into the V/T port.
    The red plug (or the single wire going to the red plug's middle pin for that matter) goes to the volts you want to measure. Most people just plug this into any empty channel on your receiver, as the middle pin of every channel gives positive volts - but this will give you the voltage at which your electronics are running which is not necessarily the same as the battery (although you'll see volts drop somewhat as the batteries deplete)

    You could also tap this wire from the battery's positive terminal but this may require some soldering or tinkering which you should only do if you know what you're doing. (Traxxas used to sell battery taps like this but they don't fit newer battery sockets, which sucks... so you'll have to make your own.).
    Then the loop on the black wire goes around your motor or wherever you want to mount it to measure temperature.

    All of the sensors can be configured and arranged in dials or gauges on the Link app's Dashboard, which is pretty intuitive so I'll not go through that here.

    Most Traxxas models will give you a Speed reading, which is a guestimate of how fast the model is going based on RPM and gearing ratio and tyre size. You can adjust gearing ratio settings in the Link app, but the speed reading you get will still be an estimate - if you want to get accurate speed readings then read on...

    Some Traxxas models will also give you other readings like the Amps the ESC is drawing, without the need for any sensors.

    So isn't this good enough? Who would want more than this? Enter The Telemetry Expander 2.0
    Telemetry junkies soon realise that they want more volt sensors and more temperature sensors. It is not good enough to know your motor's temperature. Maybe you also want the ESC temperature or your battery temperature. Maybe you want to measure volts at different places. Like maybe directly off the battery's positive port AND from the receiver subsystem.

    And most importantly, if you want accurate speed readings independent of tyre size or gearing, you will need a GPS. Yes, Traxxas provides a GPS sensor just for the fun of knowing your speed (or maximum speed). This may seem silly to some people, but for some models (especially high speed models) this will be very relevant.

    If you want to use the GPS, you have to get the Telemetry Expander. There is no way around it.

    Here you should be careful. There is a Telemetry Expander and a Telemetry Expander 2.0. Both are still for sale. You want the 2.0.
    Look carefully at the part numbers or (like me) you'll purchase the wrong stuff a few times.

    The new models have an "X" at the end of the part number.

    Old (don't get these)
    Telemetry Expander (6550)
    GPS (6551)
    New ones
    Telemetry Expander 2.0 (6550X)
    GPS 2.0 (6551X)
    You can also buy these two together, which is labelled as part 6553X
    The old and new ones cannot be mixed. 6550 will not work with 6551X



    Some models may require a bracket to allow for installation of the Expander. Like this one for the TRX4.

    The sensors used by the Telemetry Expander are not the same sensors used by the TQi Receiver
    So this took me a while to figure out because it is just not clear on Traxxas's own website.

    Above I mentioned the 6521/6523 T/V sensors that plug into the TQi Receiver (three-pin). These do not fit into the telemetry expander.

    The Telemetry Expander uses a different kind of FOUR-PIN sensors (often with black and blue wires) and it is not possible to plug the normal sensors (mentioned above) into the Expander. The Telemetry Expander sensors are often labelled as "auto-detectable xxxx sensor"
    Auto-detectable temperature sensor (6526)
    Auto-detectable voltage sensor (6527)

    Connection options for the Expander
    The normal way to connect the Telemetry Expander 2.0 is to use the 4-pin data link cable to connect the comms port on the receiver to the designated port on the Expander. But there are two other ways it can also be connected, which is not well understood or documented.

    If you vehicle as lights, it has a High Voltage Power Amplifier which plugs into the ESC. The High Voltage Power Amplifier can connect directly to the normal comms port on the Telemetry Expander 2.0 using the Maxx Data Link Cable (6565)
    (This then replaces the normal comms cable between the Receiver and the Expander).
    I'm not sure why one would want to connect this way, but on one of my own models I found that unless I connect in this way, the Link App does not detect the model's lights. (see this thread).

    One can also use Data Link Cable (6566) to connect the Telemetry Expander 2.0 directly to the ESC.

    As far as I can tell neither of these methods reduce any of the normal functionality of the Expander.


    So that's my 2c. Hope this helps and deconfuses some of the purchases needed to be made to get into this. Please post corrections or questions in this thread.

  2. #2
    RC poster
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    [reserved for future edits]

  3. #3
    RC Enthusiast
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    Very nice post. Thank you

  4. #4
    RC Competitor
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    Very well written, I had to learn of the above too during all of my Telemetry upgrades.

    The RPM sensors aren't really required for the newer models as they read speed via the ESC or even better the GPS module.
    I went and bought the rpm sensors and magnets in the beginning and then realised I didn't need them on my X-Maxx 8S.
    Last edited by morch_66479; 05-15-2020 at 06:45 PM.
    Getting back into the RC game after 10 years!

  5. #5
    RC Champion NYbandit33's Avatar
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    You can still use the 6541 tap with the newer batteries. The newer plugs are a little bigger but they still connect to each other
    Monster Baja Sla2h VXL
    Rustler VXL

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