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Transmitter changes from PPM to PCM by itself

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Old 07-16-2006, 09:22 AM
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T.W.
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Default Transmitter changes from PPM to PCM by itself

Has anyone noticed this by Alex Whittaker on page 64 of the July 2006 edition of RCM&E: ". . . . the transmitter somehow had decided unilaterally to swap from PPM to PCM, but that's another story"

I intend 'phoning the magazine's office to see if I can establish what the full story is - maybe I'll call them sometime tomorrow. The reason for my interest is that this exact same thing has happened to my new Futaba FF9 - twice! I know it sounds like a very unlikely story, but it's true and I'm really interested to find out exactly what happened in Alex's case, and what he did to fix the problem

But in the meantime, here's what happened in my own case: I was in my workshop when I switched-on my Tx and changed it to a new model's setting, ready to start setting-up the servos in my latest model's wing. The setting-up session went without problem and when I'd finished I changed the Tx back to the model settings it was originally set to, ready for the next day's flying session

A few days later and back in my workshop, I changed the Tx to my new model's settings again, this time in order to set-up the throttle, elevator and rudder servos - which all went-off without any problems. I turned the Rx and Tx off to make some adjustments to the servo horns and when I turned them back on again I found that the servos did not respond to the Tx. In fact they progressed to full deflection in "glitch-like" small movements, no matter what I did with the sticks

At this stage I turned-off the Rx in my new model and changed the Tx to a different model's settings (in fact to the model I had flown the previous day). Turning-on this model's Rx I discovered that these servos also refused to respond to my stick movements, instead they "glitched" their way over to full defllection. At first I thought that I should change my new Tx's Xtal, but as it's the synthesised version it doesn't use Xtals! It was only then that I realised the Tx had changed itself from PPM to PCM! Changing back to PPM "cured" the problem and I assumed that I must have done something wrong to cause the change-over . . . but what?

Over the next couple of days I went flying, using the older model's settings, without anything whatsoever going wrong. But a few days later the Tx again changed itself from PPM to PCM - in almost exactly the same circumstances as the previous time it happened

I really don't know how this can happen and before I 'phone the magazine's office tomorrow (or maybe a little later, depending on any response to this post), I wondered if anyone else has experienced this strange and potentially dangerous phenomenon. To me it seemed on both occasions that the change-over occurred either when the Tx was turned-off, or as it was being turned-off or turned-on. But it certainly hasn't happened during actual use . . . . yet!

So, has anyone else had this happen with their Tx? Or maybe someone knows how I could have made the change-over in error? This is not my first computer Tx by the way, I also have an FF8 and a non-synthesised FF9, so I do know my way around the settings - apart from this particular problem of course

Tony
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Old 07-16-2006, 07:42 PM
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Default RE: Transmitter changes from PPM to PCM by itself

Why don't you take this to the Futaba manufacturers forum?
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Old 07-17-2006, 04:23 AM
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Default RE: Transmitter changes from PPM to PCM by itself

OK
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Old 07-17-2006, 10:15 AM
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Default RE: Transmitter changes from PPM to PCM by itself

Did you have a mobile phone near to the tx at any time?

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Old 07-17-2006, 04:19 PM
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Default RE: Transmitter changes from PPM to PCM by itself

Hi Harry, Interesting point - but the answer is no. I was in my workshop on both occasions when the Tx changed from PPM to PCM and my mobile was two rooms away. On the other hand I've had mobile and Tx right next to each other at the field with no problems. I spoke to Graham Ashby this morning, editor of RCM&E. He gave me Alex Whittaker's email address so I've written asking him what turned-out to have been the cause of his PPM/PCM problem. I'll let you know what he has to say whenever I hear from him. Interesting, no?

Tony
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Old 07-18-2006, 04:17 AM
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Default RE: Transmitter changes from PPM to PCM by itself

Does anyone have a URL for the Futaba manufacturers forum please?

Tony
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Old 07-18-2006, 10:39 AM
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Default RE: Transmitter changes from PPM to PCM by itself

http://www.rcuniverse.com/forum/forumid_125/tt.htm
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Old 07-18-2006, 03:25 PM
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Default RE: Transmitter changes from PPM to PCM by itself

Thanks Deadeye
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Old 07-19-2006, 05:30 AM
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Default RE: Transmitter changes from PPM to PCM by itself

Dirtybird: It seems I shouldn't have taken your advice, according to the response my post received. Never mind though.

I received an email from Alex Whittaker yesterday saying:

"Sorrty I didd not replye earlier - I was away looking at boats. Thank you for your most interesting observations. May I play with my ZAP trannie for a while and get back to you? Your thoughts have prompted a few ideas...Incidentally might I have your permission to publish your letter in my column if my hunch is correct?"

So it seems that the "jury's out" on this one at the moment. But in the meantime the problem hasn't happened again and the Tx is performing exactly as it should, so I'm starting to think that I must have done something wrong and caused the switch-over myself. Time will tell I guess

Tony
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Old 07-19-2006, 09:56 AM
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Default RE: Transmitter changes from PPM to PCM by itself

One thing many people may not realize is that when a different model is not of the same modulation as the one you're currently using, and you change to that model, you must cycle the power before the modulation of the transmitter changes. If you don't realize this, then you may switch models and then wonder why you get no response, even though it worked when you did the original setup. The transmitter has then somehow "changed" that model's modulation type without your having changed it manually. Cycling the the power should take care of that.

On the 9C, the modulation type can be set in the model memory, but if you change to a model that has a different type, the 'PPM' or 'PCM' tag will be flashing. When you cycle the power, the modulation will then change to that of the stored model.
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Old 07-19-2006, 10:54 AM
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Default RE: Transmitter changes from PPM to PCM by itself


ORIGINAL: T.W.

Dirtybird: It seems I shouldn't have taken your advice, according to the response my post received. Never mind though.
Sorry. You would think they would want to know if something like this happens.
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Old 07-19-2006, 12:53 PM
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Default RE: Transmitter changes from PPM to PCM by itself

No Problem DB . . . . and thanks for your words Bax. I'm a bit slow where technicalities are concerned, so I will have to see if I can make my Tx do "exactly" what you say it will do. It does sound as though you are on the right track with this though, so I'll report back as soon as I have duplicated the "problem" . . . . (or not, as the case may be)

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Old 07-19-2006, 01:16 PM
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Default RE: Transmitter changes from PPM to PCM by itself

I would like to add to Bax's comment to say that your TX has a default setting. If it is PCM and you go from a model memory with a PPM setting to a new model memory, reset the memory and program the model, it will still transmitt in PPM even though the memory will say PCM. you will not notice a problem until you turn off then on the TX.
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Old 07-19-2006, 05:33 PM
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Default RE: Transmitter changes from PPM to PCM by itself

You know what . . . . this situation is starting to scare me. I'm not very technically-minded and I'm starting to think that it might be best if I just used my old FF8 or my "standard" FF9. I had no trouble with those Tx's at all. It's too late to start checking-out what you said against my new FF9 right now, but I'll give it a go tomorrow (maybe I'll understand better after a sleep!). Thanks for your comments

Tony
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Old 07-19-2006, 06:41 PM
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Default RE: Transmitter changes from PPM to PCM by itself

Always cycle the power when you change models or your situation will/can happen. It has happened on my 9c and 9Z when switching models with different modulation set either by accident or deliberately.
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Old 07-20-2006, 02:49 AM
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Default RE: Transmitter changes from PPM to PCM by itself

Thanks for this Andy. This I understand - and it ties-in with what happened with my Tx

Tony
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Old 07-21-2006, 02:45 PM
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Default RE: Transmitter changes from PPM to PCM by itself

I would return it to the service center and have them replace the PROM and batteries.
it might be your idleup switch or pitch curve that changes unrequested next time...
Someone at our field recently had such a case. Model 1 and 2 were OK. Model 3 showed broken but only once he was in the air.... The rest of the models were so damaged that he could not even load them anymore.
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Old 07-21-2006, 04:36 PM
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Default RE: Transmitter changes from PPM to PCM by itself

Phew . . . . and other sounds showing great relief were heard in my workshop this morning! After a few "false starts" I have finally got the situation sorted-out, and in the process I've learned that my new FF9 is not faulty after all . . . . it is only doing what it was designed to do when people of diminished technical understanding, like me, get out of their depth (I'm short so this happens a lot )

What happens is: Whenever the "modulation indicator (PPM/PCM) is flashing," the modulation will change to whatever mode is flashing, once the Tx has been turned-off and then turned back on again (powered-down and powered up again)

I must have missed the fact that PCM was flashing whilst setting-up my new model. And even though it was flashing, the Tx was putting-out PPM and allowing me to set-up my new model, so I did not think anything was going wrong. Given that PCM was flashing, the modulation was bound to change to PCM as soon as the Tx was powered-down and back up again. Case solved, and as I said: Phew!
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