Taranis - Odd Throttle Action

[Dave Bran]

Today I was helping someone who thought he had a faulty Transmitter.

I fixed that problem, which I won't bore you with, but along the way found another problem he'd been living with and which again he thought was a faulty Transmitter.

I first noticed that at stick down (glow engine powered plane) the carb barrel was completely closed. He had no idle down or throttle hold or cut set, he was using full down stick to stop the engine, so if he went there by mistake, instant cut!!

But there was worse.............as you increased stick from zero the throttle opened progressively to about 75% but then if you continued to increase stick the throttle snapped shut! Not the fault I was asked to look at, but I'd noticed that he was struggling with take off power and recovery from touch and go, which he said was an iffy engine and not a problem. Guess!

Putting the Taranis into Monitor proved that it WAS the Tx closing the throttle above around 75%, drop back under the trigger point and it worked normally.

Right:-

1. Other models were fine, no sudden reversal/cut, only this one model.

2. It was NOT a throttle curve.

I cured it, but for a laugh, what do YOU think was causing it?

 

 

 

Edited By Dave Bran on 06/08/2016 16:17:45

[Andy48]

You can do this by setting up a logical switch so that when throttle > 75 LS is true.

Then create a special function using that logical switch to override channel 1 and return a value of -100.

 

 

[Andy48]

Couldn't add anything more to above post as it was too long, but I'm guessing there is a simpler explanation.

You could also do a similar thing by setting flight modes.

Edited By Andy48 on 06/08/2016 17:33:22

[Biggles' Elder Brother - Moderator]

The problem is we can't guess this because it is in the nature of the Taranis that 10 people who set out to do that could probably find 10 different programming solutions as to how to do it!

BEB

PS Guess No 3 - set a special function to MAX the throttle setting a la servo driven retracts!

PPS Guess No 4 - copy the throttle channel to a GV,. test it and reset it to -100 whenever greater than some threshold value.

 

We could go on all night....

Edited By Biggles' Elder Brother - Moderator on 06/08/2016 19:18:09

[Dave Bran]

Except none of the offered solutions so far are things that a person that could not make the Tx say "bombs away" on a switch operation and thinks binding is a really difficult task would be remotely likely to do or stumble across............................he did not set out to do it...........it happened to him!........

[Andy48]

Posted by Biggles' Elder Brother - Moderator on 06/08/2016 19:14:24:

We could go on all night....

Edited By Biggles' Elder Brother - Moderator on 06/08/2016 19:18:09

At my age that is not a possibility.

[Bob Cotsford]

I've had odd things happen when using 'throttle trim idle only' with less than +-100 set on the throttle output, but in that case nothing happened below 1/2 throttle, then all movement was from 0 to +100 - now if you reversed the throttle action, what would that do?

[Andy48]

Seems like we're never going to find out .....

[Denis Watkins]

Itis an odd set up servo arm going past full travel at 75% , past optimum, then starting an opposite travel?

[Denis Watkins]

Thus closing the throttle

Edited By Denis Watkins on 08/08/2016 13:12:19

[Dave Bran]

That would ramp down throttle beyond the point of change, this was as stated "snapped shut", get to around 75% smoothly increasing stick and throttle snapped to zero, instantly...........

You lot give up quickly!! TEE HEE

[PatMc]

Yawn.

[MattyB]

Even speaking as a fully diagnosed OpenTX nerd(!) there is no point in this thread. As BEB points out there are lots of ways you could achieve this behaviour, so having us guess is somewhat futile. Just post the answer and maybe we can all avoid a similar "gotcha" in future (though speaking as someone who always pre-flights their models thoroughly I am struggling to understand how anyone would consider flying with such a setup).

[Dave Bran]

Posted by PatMc on 08/08/2016 13:33:56:

Yawn.

Nobody's forcing you to come here, so don't......................

[Andy48]

As Beb says its pointless Dave, there are many ways this can be achieved. If its important and we ought to take note of it, tell us, otherwise I for one am not going to keep guessing.

[Dave Bran]

Point is, AFAICT, he had no mixes set, no throttle curves, no flash programming at all (most of which you'd never get to by simple keying accident anyway, and he's not up for it). There was nothing I could find that I would have expected to set throttle to minimum as the stick was raised, the only abnormalities being IMO (right or wrong) trivial ...........

I stopped it happening by looking at what WAS set which was a throttle up end point at 79% and putting this back to default 100%. (which did not overrun servo travel at the throttle so why it had been done is, well, "uncertain", unless someone helping him decoded he didn't need that much power"

This immediately on monitor showed throttle being where the stick was, right up to full stick, no sudden cut back to bottom stick -100% at around 75-79% any more. Servo now (inevitably) operated normally over its whole range.

The ONLY other thing was that the default 1500uS servo setting for throttle was "off default" down at around 1350uS from memory.

So, why was an end point setting below 100%, even combined with a relatively minimal uS setting change, causing the throttle servo to be instantly zero'd (-100) when the premature end point was reached? Servo travel should stop at end point, not go full neg, Right?

I have no idea, so wanted to see without leading the witness if anyone had been there or had similar.

[Bob Cotsford]

Posted by Bob Cotsford on 06/08/2016 20:55:54:

I've had odd things happen when using 'throttle trim idle only' with less than +-100 set on the throttle output, but in that case nothing happened below 1/2 throttle, then all movement was from 0 to +100 - now if you reversed the throttle action, what would that do?

so much like my case where less than +-100 on the throttle output revealed a bug limiting movement...

[MattyB]

Agreed, that does sound like a bug. What version of OpenTX is/was he running, is it repeatable on another TX with the same version, and have you reported it via GitHub?

Edited By MattyB on 08/08/2016 17:32:44

[MattyB]

Just tested in Companion 2.0, and could not get it to reproduce what you saw; the throttle operated smoothly and stopped at 79%. I could not set servo mid-point as low as 1350us though (lowest achievable value with endpoint at +79% was 1375us).

EDIT - 1375us appears to be the lowest settable PPM centre value irrelevant of all other settings on the servo menu. If somehow he had managed to get it lower than that (who knows how, but go with it for moment) it's possible would strange behaviour would result, as presumably the rest of the firmware is not expecting a midpoint that low - maybe it will encounter some kind of value out of range error it can't handle?

Edited By MattyB on 08/08/2016 18:15:32

[Andy48]

Using Companion 2.1 you can get PPM lower than 1375.

If it is a bug, it has obviously been cured in later versions. Given this person's knowledge level he was probably using the original version of OpenTx which was loaded on the Tx, possibly OpenTx 1. If so, moral is its always worth updating.

One could always trawl through closed Github issues if you've a month or two to spare!

The 79% is easily explained. If converting a plane which had a Spektrum receiver, you would set the servo travel to 79% as Spektrum gear does not have the same range of servo travel as the Taranis. Max extended limits on the Spektrum is equivalent to the Taranis 100% (which is why it is better never to use extended limits on the Taranis). PPM centres differ between makes also, though the Taranis and Spektrum are the same here. It sounds like your friend has done a little reading/ video watching/advice taking, but has not read enough to understand what is going on.

At this point I've probably put quite a few off moving over to Taranis!

[Shaunie]

The 79% is easily explained. If converting a plane which had a Spektrum receiver, you would set the servo travel to 79% as Spektrum gear does not have the same range of servo travel as the Taranis. Max extended limits on the Spektrum is equivalent to the Taranis 100% (which is why it is better never to use extended limits on the Taranis). PPM centres differ between makes also, though the Taranis and Spektrum are the same here. It sounds like your friend has done a little reading/ video watching/advice taking, but has not read enough to understand what is going on.

At this point I've probably put quite a few off moving over to Taranis!

I've been considering Taranis, no you haven't put me off but the servo travel part concerns me. In my naïveté I believed that most systems had servo centres at 1500uS (I know some are 1350uS) with +/-500uS as 100% travel. So what yo are saying is Spektrum says that's 125% and Taranis says that's 100%.

The wonderful thing about standards is there are so many to choose from!

Shaunie

[Andy48]

Spekky and taranis have servo centres at 1500, Futaba uses 1520 I believe.

Normal servo range on a Spekky is equivalent to about 80% on a Taranis.

If converting over the best bet is to first ensure that the flying surfaces don't need any trim, rather than relying on Tx trimming. Next measure and record the various throws. Then swap over receivers, and I would suggest altering the throws on the model to use the Taranis 100% range. Sounds a pain, but it never does any harm to check the trimming of a plane. I've got some Emax servos that do very strange things if you go too far beyond their advertised limits.

Finally to make things easier, the Taranis has an instant trim function. Get the plane up in the air and flying level with the sticks, then flick the instant trim switch and it will set all the trims for you.

You can read up on using servos with Taranis here:

**LINK**

You want reference section 3 part 1 pages 28 to 30.