Er9x setup buddy box Instructor/Student

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This is a breakout from the original ER9X Firmware manual, with additional information about the PPM fix and other tid bits to make using two 9x radios together as a buddy box system easier.

In the manual you will find this under - Trainer/PPM IN

Before proceeding , ensure you've done the following.

(This step is no longer necessary if you are using r750 or later. Mike B. came up with a creative fix through software.)

For two flysky/turnigy 9x radios to function together in this setup, you need to do the ppm fix.

One way to do this is shown here.

* PPM In Fix for the 9x

Another way to do this fix is in the module itself.

* Info arriving shortly

It would be advantagous to do the fix in both radios. (you can however let the module dangle on the slave/student unit) If you have the DSM or Frysky moduels installed, you do not have to do the PPM fix. (If anyone has had issues, please post on 9xforums, and we can update the wiki accordingly)

* Once you have the mod done, proceed.


Instructor Setup

  • Step 1: Make sure the model is setup and working in the instructor radio before you start doing anything related to the trainer function. This way you won't have to redo a bunch of settings later.
  • Step 2: Enable the trainer function. Go to the radio general settings page 2/6. You get there by long pressing the left key and then scrolling over to it.


 This menu allows the PPMin (trainer) inputs to be configured. The PPMin signal is generated by the student Tx.
 It is the same stream of pulses that is sent to the Tx module normally.  This screen enables the RAW PPM inputs to be 
 selected to replace the sticks for training purposes. Depending on what you have connected as a student transmitter
 the channel order may be different.  JR/Spektrum radios will have TAER, where as a Futaba radio will use AETR.
 All the mixes on the instructors Tx will be applied to the student inputs. If, for example, you have expo on 
 your sticks, this will be applied to the raw trainer inputs when they are selected.
 The mode entry selects how the PPMin value is used:
  • off  : >unused<
  • +=  : add to instructor stick value
  •  :=  : replace instructor stick value
 The % entry applies a weighting to the PPMin value -100 to 100, Use -100 to reverse the input. Use 
 values closer to 0 to reduce the students control sensitivity.
 The src entry selects the PPMin channel for the function.
 The sw entry selects the switch used to action the trainer operation.
 Multiplier 1,0 to 5,0 scale for PPMin values
   The multiplier does as it's name suggests.  It multiplies the ppm Input by a set amount.  Great for 
   dealing with different tx's whose makers don't know how to encode PPM.
 CAL  Center calibration for first 4 PPMin values
 This entry allows you to calibrate the mid point for the first 4 input PPM channels.  
 Highlighting “Cal” and pressing [MENU] will calibrate the mid point for all PPM IN channels.
 PPM IN is read from the signal at the trainer port of the Tx.
 There is an option for each model to enable or disable the trainer input function. If you do not need the 
 trainer function you may disable it, and use the selected switch for something else. All the PPMin 
 values are available to the mixer.
  • Step 3: For most buddy box setups you will want the student to have full control when you flip the trainer switch. There are of course many options, see the "other options" section below for more information. For now set all 4 modes to ':=' or replace.
  • Step 4: Next you will need to set the switch column. Set all of these to TRN.
  • Step 5: At this point you should have the student Tx available. If you are going to use an Er9x Tx as the student follow the directions below for setting up the student mode. Have the instructor Tx on and in the trainer(2/6) setup menu. Plug the trainer cord into the instructor Tx and then into the student Tx. The power switch must remain off on the student Tx. It will turn on automatically when the cord is plugged in to it.
  • Step 6: Centre the sticks on the student Tx, including the throttle. Now highlight 'Cal' in the Trainer setup menu on the instructor Tx. Press and release the menu button on the Instructor Tx. All of the values to the right of 'Cal' should have changed to zero. This is how you calibrate the centres from the Sstudent Tx. In order to check that this calibration has been successful, you should move the sticks on the Student Tx to their fullest extents and make sure that each stick has a range of about -100 to 100.
  • Step 7: This step requires a little bit of work on your part. The type of student Tx determines which source channel goes with which function. I am used to Futaba so my student Tx has the channel output order of AETR. You will notice the list on the left side is RUD, THR, ELE, AIL. This means I need to set the src column as ch4, ch3, ch2, ch1 starting from the top. If you are in doubt about which channel is where the try setting them up 1 at a time. The numbers at the bottom of the screen next to 'Cal' are the PPMin input values. You can move a stick on the student Tx and watch for which value changes at the bottom of the screen. The channels are numbered from the left.
  • Step 8: You are now ready to test the controls. If you find a control is reversed you can reverse it by changing the % value in the trainer setup screen of the instructor Tx to -100. Or you can reverse the channel in the student Tx.
  • Step 9: In the MODEL SETUP menu set the TRAINER parameter on the chosen model to ON.
  • Step 10: Go teach someone to fly. Remember turn on the instructor Tx first. Then connect the trainer cord to it, and then connect the trainer cord to the student Tx with the power switch off. To power down just do the opposite. Unplug the student Tx, then unplug the instructor Tx, and finally turn off the instructor Tx.

Student Setup

This part is a bit simpler that the Instructor side. There is no need to configure the general radio settings page for the student side.

  • Step 1: Setup a basic 4-channel model in er9x. Most trainer setups only require the 4 stick inputs, this will give you that. Don't set PPM 4ch, this seems to confuse another Tx running er9x. Set it to either 6 or 8 channels output. The default is 8ch.
  • Step 2: Turn on the student Tx and make sure that your simple 4-channel model is selected. Once done turn the radio back off.
  • Step 3: Turn on the instructor Tx, then plug the trainer cable into it.
  • Step 4: Do not turn on the power switch of the student Tx! Just plug the other end of the trainer cable into the student Tx. The student Tx will turn on.
 In student mode the 9x will be in a reduced function mode.  The radio will not make any sounds,
 and the Tx module is off so no signal is being transmitted.
  • Step 5: Double check all controls work as they should. Both on instructor and from the student Tx. Learn how to fly!! Have fun!!
  • Step 6: To turn off the student Tx when finished flying. Simply unplug the trainer cable. The trainer cable will also need to be removed from the instructor Tx or it will stay on.
  • Note: There may be a problem with the trainer output with some Tx modules as, when they are not powered they overload the signal. In the Radio Setup menu, set the Enable PPMSIM setting to ON. This uses a different signal route internally that bypasses the Tx module.

other options

What else can you do with this trainer setup?? By leaving some of the controls set to off you can give the student only partial control of the aircraft. Or using the add function you can retain some control, to assist the student (probably great for young kids). You could assign your dual rates switches as the trainer switch. So automatically the Tx would switch to low rates with a lot of expo when the student has control of the aircraft. I'm sure there are many more things you could think of to do. Remember the Er9x motto 'Expanding possibilities'.

Going beyond channels 1 to 4

This entry is thanks to

In addition to mapping the usual channels 1 to 4 for the student it is also possible to pass control to the student Tx for Channels 5 to 8. These are available as sources in the mixer, called PPM5 to PPM8. They are not shown in the Radio Setup screen i.e. page 2/6 but they are still there if you no how to select them. As an example on both the instructor and student Tx's you might have: CH05 +100 P1 to control flaps from pot P1. On the instructor Tx just insert another line on channel 5: R +100 PPM5 Switch(TRN) This is a 'Replace' multiplex mix. When the TRN switch is ON, channel 5 will output the fifth channel from the student instead of the instructor Tx value from P1, thus passing control of the flap deployment to the student. You can do this with all kinds of inputs.