Odd effect seen when setting up throttle range

[The Wright Stuff]

I currently have an issue with setting the throttle control on my particular combination of ESC and transmitter. It's a little obscure, so let me try to explain it carefully.

I use a Futaba 6J, which has a throttle cut switch, which can be set to ESC mode to disable the throttle control. I use this pretty much all the time when carrying 'live' models to and from the pits, since it will prevent the motor from starting if the throttle lever is accidentally knocked.

This works perfectly on my Dynam, Parkzone/E-Flite and Durafly models, but I encountered a particular issue when I tried to set up a 10A Hobbyking ESC for a glider that I recently converted.

What happens is that the ESC is 'taught' the throttle range in the usual way, through full stick deflections. Then the motor reaches full power when the stick is fully up, and stops when the stick is fully down. So far so good - and yes, have remembered to reverse the throttle on the Futaba Tx. I can switch the throttle cut on, and the throttle function is disabled. But when I switch the throttle cut off, the motor bursts into life, even though the throttle stick is still fully back. Thankfully, the model was restrained the first time I discovered this. Further investigation (switching off the transmitter) showed that the failsafe also does not now stop the motor, despite being previously set.

My conclusion is that I am somehow inadvertantly entering the ESC 'teach' mode by activating the throttle cut switch, and then the limits are overwritten such that the fully back throttle lever position no longer corresponds to motor stopped. It's infuriating.

I can probably find a work-around by messing around with the EPA for the throttle channel, but I wondered if anyone else has seen this problem, or a similar issue. Either there is a fault with the ESC, or it simply doesn't like the way that Futaba communicates the throttle information...

[Martin Harris - Moderator]

Thinking out loud:

Can the throttle cut setting be reversed - i.e. is it simply setting the throttle to the Futaba closed position (full throttle for everyone else).

Was the throttle trim zeroed before setting the range?

Is the ESC one of the (thankfully) rare examples that activate the throttle on loss of signal/power?  I have come across one or two in the past where switching off a receiver battery before disconnecting the flight pack activates the motor! A quick scan of the Futaba manual suggests that it "disarms" the ESC - perhaps by removing the PPM signal?

Edited By Martin Harris on 31/05/2016 11:15:34

[Chris Bott - Moderator]

Without thinking about this very deeply, TWS, I'm wondering if both bottom stick and throttle cut are giving exactly the same servo position? They should, but is it possible that they could be set to be different?

[The Wright Stuff]

Posted by Chris Bott - Moderator on 31/05/2016 11:34:18:

Without thinking about this very deeply, TWS, I'm wondering if both bottom stick and throttle cut are giving exactly the same servo position? They should, but is it possible that they could be set to be different?

There are two modes that the throttle cut button can be configured in: one for IC, and one for ESCs. The purpose of the button is totally different for each mode, hence I assume the action of it is, too.

For IC, the purpose is to enable the throttle servo to be set 'beyond' the bottom stick travel, such that you could cut the engine by pressing it, but without accidentally killing it when throttling back - it's basically a replacement for fiddling with the trim levers.

But in ESC mode - I'm not entirely sure how it works. It doesn't mimic a particular stick position, but rather communicates directly to the ESC in some 'clever' way that I can't really fathom.

I may well be answering my own question here: I could simply 'pretend' the ESC is a servo, select IC mode and get rid of the 'trying to be too clever'. At least then I can just plug a servo into the channel and see what it is actually commanding!

[Allan Bennett]

You could plug a servo into the throttle channel with the throttle cut in ESC mode, and see what it does. But take the prop off first!

[Chris Bott - Moderator]

I would be very surprised indeed if a Rx communicates with an ESC in any way other than with standard PPM servo pulses.

If you use the IC setting then I think you're asking for trouble because there are two different throttle low settings. At some point the ESC could well learn the wrong one. In fact it fits your symptoms that that is just what it is doing.

[The Wright Stuff]

Posted by Chris Bott - Moderator on 31/05/2016 20:33:53:
I would be very surprised indeed if a Rx communicates with an ESC in any way other than with standard PPM servo pulses.

If you use the IC setting then I think you're asking for trouble because there are two different throttle low settings. At some point the ESC could well learn the wrong one. In fact it fits your symptoms that that is just what it is doing.

Yes, sorry, if I wasn't clear. I think it must use servo pulses, but it doesn't appear to be influenced by the channel settings on the transmitter: i.e. the PPM signal sent when throttle cut operates is independent of end points, trims, subtrims, rates, etc.

So what I need to find, experimentally, is the 'throw' setting in terms of the end point adjust, that best mimics this state in terms of the output signal from the receiver.

It's all part of the fun!

Edited By The Wright Stuff on 01/06/2016 09:23:35

[Robert Armstrong 2]

Had something similar. Cured by setting the throttle trim all the way down.