Suggestion - smooth start for ESCs

Info and discussion about the original AQ v6 flight controller

Suggestion - smooth start for ESCs

Postby hogster » Thu May 08, 2014 8:48 pm

Hi all :)

I've had limited experience of the DJI flight controllers, but one feature I do like which I feel is missing from the AQ is the smooth / very slow startup when arming the motors. I can't help thinking the rapid start-up was a contributing factor to the death of one of my ESCs dying, before I even managed to take-off :(


(password: hogstercortex)

It could have had nothing to do with that of course!

Many thanks for your thoughts! :) David
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Re: Suggestion - smooth start for ESCs

Postby Max » Thu May 08, 2014 9:15 pm

With properly calibrated/set up ESCs, AQ motor startup is typically very smooth. No offense meant, but I think you're focusing on the wrong issue. Even if AQ commands full throttle right off the bat (which is definitely not the case in the video), the ESC shouldn't just burn up, and the actual motor starting should still be smooth. Either the ESCs aren't calibrated right, don't like those motors for some reason, or are just junk. IMHO :)

-Max
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Re: Suggestion - smooth start for ESCs

Postby JussiH » Thu May 08, 2014 9:18 pm

"Rapid start" very likely had nothing to do with your ESC failure. Unless the start itself drew an overwattage, there is not much likelyhood of the start beeing the problem, unless it cocked on 1 phase and keep it open. That is not unseen but its pretty rare.

Soft start is also a ESC feature, not a FC feature - I do beleive its already in the BL-Heli wares, dunno about Afro and SimonK´s.

However, I think its a good idea to make soft start....but its not something I could do - so its up to Bill to find time for it....maybe for V3.

Soft start comes from helis and gear driven propellors, where its used to protect gears and pinions from stripping out when the motor start. So as a feature for a MR its pretty useless, but it has a high "cool" factor...
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Re: Suggestion - smooth start for ESCs

Postby Max » Thu May 08, 2014 9:41 pm

CP helis can afford a "soft start" because they don't stop the motor while in flight. Airplanes can glide, so startup speed isn't as vital (though who uses gears on those anymore?). On a MR it seems not only useless, but potentially dangerous. Unless the motor is never allowed to stop completely in flight (which I realize has been done before, back when many ESCs couldn't be counted on to start motors smoothly). Or am I missing something?

-Max
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Re: Suggestion - smooth start for ESCs

Postby JussiH » Thu May 08, 2014 10:03 pm

Soft start is only the actual start itself, Once running it has no effect. All it does is to make sure that there is no abrupt torque moment applied to gears and pinions that cant take it. Same thing for ESC "braking", its designed to stop the prop fast, once you pull throttle low. The purpose is to make sure you can stop prop fast in a landing situtation, but has no effect on running ESCs.

Back in the old days before I learned about flashed ESCs, I ran OEM-ESCs with soft start and braking enabled, and it made absolutely no diff in flight...But I liked that I could stop the props instantly and the soft start looked cool.

Soft start is done by MK on their ESC´s. Basically it starts the motor and then softly spools it up to min level. From there on it acts normal. But its just cool, not useful...

Actually, now that we are talking ideas....I think that a "brake" option would be nice for MR´s. A way to make sure that prop stops very fast, if throttle is pulled to 0 - sort of an "emergency stop"
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Re: Suggestion - smooth start for ESCs

Postby JussiH » Thu May 08, 2014 10:09 pm

One more

ESC32v2 already employs a strategy for "soft start", although it works different than traditional soft start.

If you hook an ESC32 up to a servo tester and then crank the servo tester up to half, then ESC32 will first start the motor at a low RPM for a short period (maybe 1/10 of a second) and then go to the commanded duty as fast as it can. I guess this is done to make sure the motor is started properly before a big duty increase is accepted.
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Re: Suggestion - smooth start for ESCs

Postby hogster » Thu May 08, 2014 10:51 pm

Interesting discussion! I must digress I like the cool factor of the slow start too ;) but I'm interested that you don't think it had anything to do with the burning up - I was just throwing around some ideas really in the hope of coming across the real cause!

I like the sound of the ESC32 soft start, and anything to protect the ESCs against unnecessary surges in current is probably a good thing?

Cheers :) David
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