Buddy Box Training Radio Links & Control Congruence

[Capt Kremen]

Recently I was made aware of an issue which had not, to the best of my knowledge, shown itself before.

On linking a MPX Cockpit Tx to a MPX SX Tx Handset for training purposes via Bluetooth wireless link, on transfer of control from Master/Teacher Tx to Pupil Tx and subsequently back, some control surfaces moved to adopt slightly different neutral positions. (Enough to potentially cause a change of model trim).

I repeated the test and observation using two Spektrum Tx, (a DX8 & DX6i via cable connection), similar slight changes in control positions on transfer were noticed.

In both instances, all Tx trims were centralised to begin with i.e. not off-set, all Tx fully charged/fresh batteries installed and the same Rx and model installation servo used.

Control end-points checked as well as any mixes which might be present, no obvious cause except perhaps component variance e.g. pot resolution(?)

Searching through the manuals of both radio manufacturers, I can see no mention of this anomaly or how it might be rectified or compensated for.

Obviously the Master Tx flying a model in trim then transferring control to a pupil Tx with it changing trim/control position is not ideal or desired.

Have others noticed this with their training link/buddy-box set-ups?

If so, how did they resolve the issue?

Once the pupil has enough flights under their belt/log book, the teacher probably intervenes and takes less control, so the issue is likely less noticeable but the crucial initial first few flights are likely to be critical.

[Murat Kece 1]

I had exactly the same problem recently in connecting a DX8E and DX9 for training.. The trainee was getting reduced control ranges.. I will be pleased to hear if there is any remedy?

 

[Frank Skilbeck]

Dave PM'd me about this and so I did a few tests as follows 

1) MPX Profi as teacher and Sx as student, from what I can observe the Sx doesn't always return to the same centre. The Profi servo monitor screen can display graphs or % movement, when the trainer button was depressed and I moved the Sx stick the centre could be +/- 2% off, this meant that sometimes there was a small servo movement and not others. I only hooked up servos to the aileron and elevator channels and on my Sx it was more pronounced on the aileron than elevator. So it wasn't so much as a mismatch but the Sx not centering  accurately each time. So if you handed the model over to the student, the model might then turn, climb or dive slightly, but then be OK when the student corrects on the sticks. 

2) As an experiment I substituted my Royal Pro as the student set, on the servo monitor the same happened but to a much smaller degree, +/- 0.5%, and you couldn't see the servos move.

 

So in conclusion I think it's down to the stick pot resolution and how well the sticks center, would be interesting to see if the newer hall effect sticks are better in this respect. Note on MPX transmitters when in buddy mode the student Tx only transfers the stick positions the trims stay on the teacher Tx, on some other sets I've used you have to trim the student Tx separately.  I also teach with a Spektrum Dx6i/Dx6 (the original DSM one) but haven't checked if there is any offset when handing over, or whether we've just corrected for that on the trims.

 

What I always try to do when checking a model on a buddy box set up is have an experienced modeller check out the student transmitter first, that way we know whether any drift is the model or the student!

[Max Z]

One way to mitigate this is to use the Teacher/Student switch simultaneously as the flight mode switch. As each FM has its own trim settings you should be able to get the plane trimmed in both modes. But you do indeed have to have an experienced pilot to stand in for the Student during this. And remember that you have to synchronise stuff like stick travel and expo (not dual rate) for both FM's (and some of the stick mixers).

Note that I am familiar with the Multiplex Royal SX only, not Spektrum.

 

Max.

Edited February 28, 2023 by Max Z

[Andy Gates]

You could try rebinding or remaking the link.

 

I came across this once using mixed radios and relinking the Tx's sorted it.

[Capt Kremen]

Thanks Andy, tried that several times, still a trim/control variance of up to 5mm approx. (elevator and aileron in my case), between Tx switching 'tween the two.

I am curious to know how many others and with other radio makes e.g. Futaba, FrSky, HiTec etc. this difference occurs. 

Could explain away a few of the 'difficulties' encountered between the Teacher & Pupil, especially during early stages when getting to grips with just keeping a model in the air!

[Denis Watkins]

If you check on the Tx Monitor, you will find that at middle stick, some show the cursor off centre.

The sticks need " Calibrating " where full deflection is set in the four corners of the stick movement and it's centre.

Look up " Calibrating " the sticks for your Tx.

[Capt Kremen]

Whilst the MPX 'Cockpit 12' Tx has calibration capability, (carried out and indicating successfully all correct), the MPX 'Smart SX' Tx handset/controller does not have any LCD display and no description of a calibration process appears in the MPX manual accompanying the set. With the MPX set-up, the control surface variance remains. 

I will set up a Spectrum 'buddy-box' test rig using two fully re-calibrated Spektrum Tx and see if they (still) indicate a control difference on switching between.

[Frank Skilbeck]

1 minute ago, Capt Kremen said:

Whilst the MPX 'Cockpit 12' Tx has calibration capability, (carried out and indicating successfully all correct), the MPX 'Smart SX' Tx handset/controller does not have any LCD display and no description of a calibration process appears in the MPX manual accompanying the set. With the MPX set-up, the control surface variance remains. 

I will set up a Spectrum 'buddy-box' test rig using two fully re-calibrated Spektrum Tx and see if they (still) indicate a control difference on switching between.

If I recall on my Spektrum buddy box set up, all the student parameters are transferred across, so you have to trim the model on both transmitters.

[Andy Gates]

Frank, I recall there is a set up in the Spektrum menu where the copying over of a model is not required for buddy box operation - can't remember its name on the menu though.

It just requires a "Trainer" model to be set up on the buddy with the master being used for all the programming / rates / trims & mixes.

[Frank Skilbeck]

11 minutes ago, Andy Gates said:

Frank, I recall there is a set up in the Spektrum menu where the copying over of a model is not required for buddy box operation - can't remember its name on the menu though.

It just requires a "Trainer" model to be set up on the buddy with the master being used for all the programming / rates / trims & mixes.

Yep on the later sets that have wireless training, the Dx6i wasn't that advanced.

[Peter Jenkins]

Does the MPX transmitter have a setting for the Trainer mode as Master and Slave?  I ask, because my JR Tx has 2 types of trainer setup.  The one I like has the master Tx set as Master in the Trainer menu and the slave Tx is set to Slave in its menu.  Now, when you connect the slave and switch to the slave using the trainer switch, the Master Tx merely reads the four stick positions and all other settings are as per those in the Master Tx model memory.  You can also set both Tx to Master but must have a memory on the Slave Tx that is identical to that in the Master Tx.  Now when you transfer control to the slave, the slave Tx reads all the model memory details on the Slave Tx.

 

Before I sussed this out, when I selected the Trainer switch the model control surfaces would move a small amount - enough to alter the model's trim.

 

Does the MPX transmitter have the same system?

[Brian Cooper]

It is probably considered by some to be a type of heresy to criticise MPX radios but, to be brutally honest, the described issues are the sort of thing which is perfectly normal for this particular marque. 

 

It is not a brand which attracts any respect in my clubs.

Inconsistent stick centering and poor stick resolution are the least of its worries.  

 

Nevertheless, I hope the problems can be ironed out a bit. 

Best of luck. 

[FlyinFlynn]

A fine example of how the passing years don't always bring progress... in my day's the only way a trim would get altered between student and teacher was if you caught the trim lever when handing the Tx over!.  🙂

 

It does sound like a resolution issue.... 

[Frank Skilbeck]

9 hours ago, Peter Jenkins said:

Does the MPX transmitter have a setting for the Trainer mode as Master and Slave?  I ask, because my JR Tx has 2 types of trainer setup.  The one I like has the master Tx set as Master in the Trainer menu and the slave Tx is set to Slave in its menu.  Now, when you connect the slave and switch to the slave using the trainer switch, the Master Tx merely reads the four stick positions and all other settings are as per those in the Master Tx model memory.  You can also set both Tx to Master but must have a memory on the Slave Tx that is identical to that in the Master Tx.  Now when you transfer control to the slave, the slave Tx reads all the model memory details on the Slave Tx.

 

Before I sussed this out, when I selected the Trainer switch the model control surfaces would move a small amount - enough to alter the model's trim.

 

Does the MPX transmitter have the same system?

With the Sx it recognises automatically when it is in buddy mode and disables the trims and just sends the stick positions. On the master Tx you have to set up the trainer mode to advise the Tx what channels to accept from the student Tx, i.e. you can say have ailerons on channels 1 and 5 on the master and channel 2 on the student, you can also decide what controls to allocate to the student Tx, so you could set it up so the master Tx keeps control of say throttle and allows the student to control elevator, aileron and rudder.

 

The Sx is MPXs low end transmitter and is a bit toy like and while it works OK I don't think it centers that well, whereas my Profi/Royal Pro and clubmates Royal Pro and Cockpit Sx's have all centre quite well and have proven very reliable, with any repairs being due to operator inflicted damage (i.e. transmitters falling off the bench!)