Strange ESC fault

[Geoff S]

Whilst taking the opportunity (rare this 'summer' for a trip up to the field my Riot mysteriously lost power. Not completely but there was insufficient for take off and it normally takes to the air with satisfying rapidity.

I suspected the well-used motor and when I got home I temporarily replaced it with another and checked using my watt-meter and a 12x6 prop. Still the drive train only drew about 8 amps flat out but ran perfectly smoothly. Replacing the ESC restored normal service and current draw up to 35 amps or so.

Now I've had an ESC fail before but that resulted in very jerky motor operation presumably because one of the MOSFETs had failed but in this case the only symptom was lack of output power.

It was very windy when I was flying and I did a rather clumsy attempt at a touch and go on our grass patch which resulted in a bent undercarriage. I straightened it and it was when the Riot wouldn't take off I found the lack of power. I can't see why the heavyish landing should cause the ESC fail (the prop was undamaged) but perhaps it did. Any ideas? It does seem to be too much of a coincidence but perhaps the loss of power at a critical point in my approach cause a stall?

Geoff

Edited By Geoff Sleath on 07/07/2016 21:08:34

[Allan Bennett]

The only thing I can think of that would result in loss of power but still run smoothly is a high resistance in the battery wire into the ESC. Either a damaged connector, or most likely, the the lead almost broken off where it's soldered onto the board. A heavyish landing could do that.

As I think you know, damage to one or more motor wire, or the output electronics, would result in jerky motor running.

[Frank Skilbeck]

I had the same happen to me, but this was with a new model, using an existing ESC, I knew roughly what amps the motor/prop combination should be pulling, but it was very feeble and amps (using telemetry) very low, I thought it was a battery problem initially but a change of ESC cured it.

[Josip Vrandecic -Mes]

Hi Geoff, I had a similar case with my MX-2 and the cause was substandard already installed ESC. I can not define what it is '' a cheap or bad '' esc but when I installed a high-quality and expensive ESC everything was fine so far. I am a regular user of RC electronics, and did not find it easy to diagnose, or repair faulty circuit boards .... of course this is my experience.

Rgds

Jo

[Geoff S]

The fault certainly wasn't due to a poor battery because the effect remained with each battery I tried. Of course there could be a faulty connection in the ESC itself but it has been performing perfectly for many hours of use.

Josip, I'm a retired electronics engineer but, like you, I find it difficult and frustrating not to be able either to diagnose or repair the ever more sophisticated electronic devices in common use. The faulty ESC didn't seem to getting hot and there was no smoke coming out. I'll cut it open and see if there's anything obvious.

I've replaced the 40 amp Century esc as supplied with the Riot with a 50 amp Black Mantis I had to hand so I hope all will be well for another few 100 successful flights.

Geoff

[Simon Feather]

I had a similar problem (very low max current draw, not enough power to take off) with the ESC in a model I was given (because it only had enough power to taxi!!).

ESC was completely unbranded, no obvious identifying marks on it. Initial thought on mine was that that the throttle end point had been mysteriously reset (easily done if power is connected whilst the throttle is not at zero and you don't immediately recognise the resultant beeps). So you could try resetting the max throttle setting but I don't hold out much hope - it didn't work on mine.

So like you, I simply replaced the ESC and now I use the dodgy one simply as a power supply if I need a BEC on the bench when setting up servos. Better than throwing it away!

Simon

[PatMc]

I once had something similar happen at the field, I think it was a re-labelled Hobbywing esc. After much frustrating messing about changing batteries etc I was about to call it a day but as a last resort before going home, I did a factory re-set of the program. Bingo, full power restored. As the model was an E-glider I just needed to change the brake setting from it's default "off".
I never was able to replicate the problem.