Transmitter Explanation Needed

Discussion in 'Getting Started' started by David A, Jul 9, 2018.

  1. David A

    David A Member

    Just starting out building and programming a drone using a Taranis X9D transmitter but my question is probably for any transmitter.
    The transmitter can use 4 basic channels for throttle, pitch, roll and yaw. But, in the case of a quad, don't a least two motors have to have their speed changed in to roll, for instance. On my receiver I plug the ESC for each motor into channel 1,2,3 or 4.
    So, how does the transmitter know which to motors to speed up or slow in order to roll left or pitch down, for example?
    Does one have to connect each motor to a particular channel on the receiver?
    And for Yaw, does it speed up two motors and slow down the other two? But how does it know which motors to affect in which way?
    Any assistance in understanding this issue would be truly appreciated!

    Thanks, Dave
  2. Jackson

    Jackson USA member at large

    It doesn't, that's the flight controller's job.
    wafflejock likes this.
  3. DrAbsurd

    DrAbsurd Well-Known Member

    The flight controller board handles those things. Not sure what you mean by esc being plugged in to receiver. For a quad to fly it needs a flight controller, power board, controller receiver, video transmitter and camera, (hooked directly together or with the FC in between) and esc boards. Some or all of these can be combined into one board but there is a part of that board pertaining to each. The FC is in control of everything you asked. It tells the motors what to do through the esc's, as it was told by the reciver. They draw and distribute the power, from the power distribution board, to each motor as it will demand.
  4. David A

    David A Member

    Thanks, Jackson, that makes perfect sense.
  5. David A

    David A Member

    Thanks, DrAbsurd, appreciate all the details.
  6. wafflejock

    wafflejock Well-Known Member

    Just to build on the previous explanations you will setup how the receiver input is interpreted by the flight controller. Think most people run Betaflight firmware/software on their flight controllers so when you plug it in over USB and run the betaflight program you can connect to the FC and program it to interpret the input it gets from the receiver however you need/want.

    First step will just be telling the FC which port you plugged the receiver into and what kind of receiver signal it is (lots of walk throughs on betaflight configuration), after that you'll want to go to the receiver tab and map the input values to throttle/ailerons/rudder/elevator (in quad terms throttle/roll/yaw/pitch) to the correct stick and make sure the sticks give values from 1000-2000 at the bottom and top. You'll also want to run calibration on the ESCs to make sure you can use their full range as well (they need to interpret the signal from the FC min-max properly)

    Once you have all the basic stuff working and you've been flying for a while you might be interested in adjusting the PID values to get a snappier/tighter feel or to remove any vibrations when making sharp turns or snap flips/rolls. Ultimately the FC takes in information from the receiver about what you want it to do and it keeps track of what has been happening and makes some small predictions based on current acceleration on what is about to occur and then adjusts all the motor speeds accordingly (this is basically the PID loop). Believe on most FCs it runs this loop of correction at anywhere from 2-8khz or 2000-8000 times a second (faster than the motors can respond in some cases).
  7. David A

    David A Member

    Thanks for all the advice and explanations!

    One more question. I have an X9D transmitter. What does the mode choice of Quadcopter do for me vs Airplane or Helicopter for example.

    Thanks, Dave
  8. wafflejock

    wafflejock Well-Known Member

    Use airplane mode. If your transmitter is setup for mode 2 (typical) the throttle on the left stick won't spring to middle it will just sit wherever you put it (mode 1 the right stick would be throttle and doesn't spring to center).
  9. wafflejock

    wafflejock Well-Known Member

    In airplane mode the transmitter is basically sending throttle, ailerons, rudder, and elevator signals to the receiver.

    The receiver passes those along to the FC and then in the FC you tell it how to interpret that input from the receiver for flying a quadcopter essentially it interprets the input as throttle, roll, yaw, and pitch then it adjusts all the speeds it expects to drive the motors at and sends that along to the escs. Basically throttle means increase speed across all the motors on average, roll left means increase speed on two right motors and decrease speed on two left motors, for pitch it's the same but front and back motors as pairs, yaw will work on changing speed of motors diaganol to each other, but the FC works out all the details and filters out noise in the signals.

    Anyhow let us know how it goes or if you get hung up configuring anything.
  10. David A

    David A Member

    Right, I understand this. But on the Taranis X9D transmitter, there is a QUAD setting and I am wondering what is different about that setting compared with the Airplane setting? What will the transmitter do differently if I choose the Quad setting?
  11. wafflejock

    wafflejock Well-Known Member

    Ah sorry haven't seen that option on my dx6i only have heli or aeroplane as options hopefully someone with that transmitter can chime in.

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