Throttle Cut and Throttle Hold Overview

In order to adjust your servos and gyro, you need to power the helicopter and put the throttle to mid-stick (50%).  The problem is that we’ve already wired up the motor, so the motor would be running as well.  Also, there will be many situations where you need to adjust the servos and linkage rods, but do not want the rotors to be turning.

So, how do we configure the Futaba T7C to kill the electric motor with a flick of a switch.  You have two options:

  • THROTTLE HOLD (TH-HOLD):
    • Throttle hold sets the throttle to a predefined value whenever SW-G is ON.  Throttle hold is normally used for auto-rotation training.  However, in our example, we’ll set the HOLD to equal 0% throttle.
  • THROTTLE CUT (TH-CUT):
    • This is very similar to throttle hold, however, you have a limited throttle range where the throttle cut switch can be used.  This is defined by the threshold setting.  The only issue with using the TH-CUT is you have to toggle the switch at radio power up for it to work.

There is a third option that you can use while building the helicopter:  set the throttle curve to 0% for all positions of the thumbstick.   For more information on throttle curves, click HERE.

Throttle Hold Example:

To configure Throttle Hold to kill the engine at any throttle speed, configure the Futaba T7C as follows:

  • TH-HOLD = OFF
  • POS = 0%
  • R-OF = INHibit
  • RT = 0%

However, if you want to use  the Throttle Hold capability to do auto-rotation training, then you should use Throttle-Cut instead.

Throttle Cut Example:

It is not obvious how to set up throttle cut for an electric motor.  Here is how I set it up:

TH-CUT -> RATE = 0%

  • The RATE is the speed that the motor will go to when the SWITCH is thrown.  Since we have an electric motor, set this to 0%, meaning we want the motor OFF when the TH-CUT SWITCH is thrown.  For a gas powered motor, you might want it set to an idling rate, say 3% or 0%.

TH-CUT -> THR = 17%

  • This is the THRESHOLD setting.  The TH-CUT feature is only active below the threshold, in my case, 17% of throttle.   Another way to think of it is that the software running on the radio will only look at the throttle kill switch (SW A) when the throttle is below that threshold.
  • If you set the threshold to say 100%, then the TH-CUT feature could be activated AT ANY THROTTLE setting, which is dangerous.  Imagine you are flying and you hit the TH-CUT switch by accident !!  You motor would immediately stop.  By setting to some low percentage say less than 5-20% you prevent this scenario from happening.  However, this means the throttle stick must be below 17% for the TH-CUT feature to work.

TH-CUT -> SW = A v  (switch A with a downward triangle)

  • Here is where you specify the switch on the radio to use to kill the engine.  For me, I chose SWITCH A.

Futaba T7C Throttle Cut Screen Configuration

Operation Behavior of Throttle Cut on the Futaba T7C

This part is a bit tricky since the TH-CUT functionality is not active at radio power up.  So here is how you use the TH-CUT feature:

  • Scenario #1 – Servo & linkage arm adjustments.  You have the helicopter on your work bench and you want to make adjustments.  You don’t want the motor turning.
    1. Push SW-A forward (kill position).
    2. Pull the throttle stick all the way back to 0% throttle.
    3. Power on the Futaba T7c radio.
    4. Toggle SW-A, that is, pull it back (TH-CUT = off) and then push it forward (TH-CUT=on).  [** THIS IS THE TRICK **]
    5. Push throttle stick forward and the motor will not turn.  At this point, the throttle cut is active and you can work on the servos.
  • Scenario #2 – Killing the motor after flight is over.  You’re done flying, you need to approach the helicopter and disconnect the battery.   For safety reasons, you want to ensure the motor does not start up.
    1. Push SW-A forward (kill position).
    2. Pull the throttle stick all the way back to 0% throttle.
    3. Power on the Futaba T7c radio.
    4. Toggle SW-A, that is, pull it back (TH-CUT = off) and then push it forward (TH-CUT=on).  [** THIS IS THE TRICK **]
    5. Once you’re ready to fly, pull SW-A (disable throttle kill) to allow the motor to turn.
    6. Push the throttle stick forward and the rotors will turn and you can fly.
    7. Once your flight is over and the helicopter is landed.
    8. Pull the throttle back to zero.  The blade should stop turning.  At this point, your throttle is below the THRESHOLD value.
    9. Push the SW A switch forward to activate the TH-CUT feature which will stop the motor.

I hope this clarifies the THROTTLE CUT feature.