ESC problem do you think?

[Tim Kearsley]

Just been flying my Ready2fly Venom, trying to get a throttle-elevator mix set correctly, to counteract a tendency to pitch down under power.

The first two flights were fine, but on the third and last there were a few "glitches" where the motor suddenly lost power, just for a fraction of a second. We didn't notice any loss of control, suggesting that it wasn't a complete loss of electrical power. I checked the Deans connectors when we landed and everything seemed OK - wiggling the connectors about didn't cause any breaks in contact.

So..... do you think it could be an intermittent or brewing ESC problem? The model comes with motor, fan and ESC installed, so I have no idea what brand or quality the ESC is. I'm inclined to have it out and fit a replacement to see if that fixes the problem.

Any thoughts chaps?

Tim.

[Tim Mackey]

Are you sure it wasnt simply the LVC cutting in - after all it was its third flight.

[John Privett]

Or possibly a momentary radio "glitch" - particularly if you're using 35MHz rather than 2.4GHz.

Also - though I know it's not the question you asked! - if you're getting pitch down with power that suggests to me that you've got too much downthrust on the motor. Wouldn't reducing that be better than masking the effects of it by adding in an elevator mix?

[Tim Kearsley]

Thanks for the responses chaps.

Tim - the nature of the interruptions didn't seem like LVC action to me. The third flight was with a fresh battery and the glitching was happening after just a minute or so, and I'm getting typically 5 to 6 minutes with each battery.

John - yes, I agree that it sounds like the thrust line isn't right - but how do you adjust that with an EDF model? Bear in mind that this is a foam ARTF, with fan already fitted. I'm not sure you can adjust the thrust line.

Tim.

[John Privett]

Posted by Tim Kearsley on 16/09/2012 16:06:06:
John - yes, I agree that it sounds like the thrust line isn't right - but how do you adjust that with an EDF model? Bear in mind that this is a foam ARTF, with fan already fitted. I'm not sure you can adjust the thrust line.

OK, fair point! I hadn't appreciated it was an EDF, though I'll admit the clue was there in the name.

One of our club members builds free-flight ducted-fan models (in the past powered by very small glow or diesel engines, his most recent is electric.) If I remember correctly he trims the thrust-line on those with small manually-adjustable (by bending) 'tin-plate' vanes in the tailpipe of the model. Might be worth a try, though I can see why a throttle/elevator mix might be easier to implement! Of course in his case that's not an option...

[Tim Mackey]

Fair enough Tim - as you say, it doesnt sound like a tpical LVC thing. As John said, is it 35mhz?

[Tim Kearsley]

No, it's Spekky 2.4 GHz kit. I think I'll extract the ESC to see what brand it is - it loooks fairly simple to get at. There's a separate UBEC to power the RX and servos, and that's a Hobbywing 5A job.

[Allan Bennett]

Not very long ago the tail of my T-Rex 500 heli kept twitching -- not enough to be a problem, but enough to be annoying. After changing the usual suspects (tail servo, and then gyro) I realised there was a momentary change of motor/rotor sound whenever the tail twitched. It was the ESC causing the motor to lose power momentarily about every half minute or so, and the change in torque was causing the tail-twitch. Replacing the ESC has cured the problem, though I have no idea why it was doing what it did. Nothing seemed to be overheating, and it wasn't lvc because it always continued running after the 'blips', without me having to reduce throttle.

[Tim Kearsley]

Very interesting Allan - that describes very well the symptom I am seeing - momentary loss of power (for a fraction of a second) and then normal operation.

I think I will replace the ESC and see what the effect is. If it turns out NOT to be the ESC I can always use a spare!

[Tim Kearsley]

Well this one is baffling me now! Today I flew the model for the first time since replacing the ESC. Result - no change!! The same momentary losses of power to the motor as before were occurring every few seconds.

Is it worth swapping out the receiver do you think?

It's annoying, because in every other respect the model is a superb flyer.

Incidentally, I put the Eagle Tree data logger on it for an experiemnt yesterday and fired up the motor - it dissipates approximately 1.5 kW!! In a model weighing around 3 lb, no wonder it goes!!

[Clifford Stone]

Posted by Tim Kearsley on 16/09/2012 20:28:53:

No, it's Spekky 2.4 GHz kit. I think I'll extract the ESC to see what brand it is - it loooks fairly simple to get at. There's a separate UBEC to power the RX and servos, and that's a Hobbywing 5A job.

 

Had this problem a few months ago, the 'cheap!' 50a ESC had a seperate, equaly cheap UBEC.  I changed the ESC/UBEC for a 'decent quality?' (cost a bit!) one that incorporated a BEC . . . problem soved, we have discused it on the field?? Concensus, the ESC was fighting the UBEC for power, as a poor power match???

I dont understand the whys and wherefores, but I dont have the problem now . . .

CJS

Edited By Clifford Stone on 30/09/2012 17:41:05

Edited By Clifford Stone on 30/09/2012 17:41:34

[Tim Kearsley]

Thanks for that Clifford. In my situation, there is an 80A ESC without a BEC and a separate 5A BEC, so there shouldn't be any "fighting".

One thing has occurred to me - could it be that there is intermittent loss of radio signal occurring? The Rx is an AR7000 and failsafe would be throttle to idle and other surfaces to last commeanded position. This could explain the momentary loss of power to the motor I guess. I'm thinking I will swap out the Rx for another and put a flight log on after the next flight to see if there is a signal quality issue.

Sound possible?

[Frank Skilbeck]

Posted by Tim Kearsley on 30/09/2012 16:54:37:

Incidentally, I put the Eagle Tree data logger on it for an experiemnt yesterday and fired up the motor - it dissipates approximately 1.5 kW!! In a model weighing around 3 lb, no wonder it goes!!

1.5KW what size battery are you using in that, for a 3lb model 450W would give endless vertical performance and it would fly great on 300W.

[John Cole]

Posted by Tim Kearsley on 01/10/2012 12:54:04:

One thing has occurred to me - could it be that there is intermittent loss of radio signal occurring? The Rx is an AR7000 and failsafe would be throttle to idle and other surfaces to last commeanded position. This could explain the momentary loss of power to the motor I guess. I'm thinking I will swap out the Rx for another and put a flight log on after the next flight to see if there is a signal quality issue.

This would give interruptions to motor power, but not I think as brief as you report,

What type of ESC have you fitted? How is the timing set?

Any possibility of bad soldered joints, e.g. at bullet / Deans?

[Tim Kearsley]

Frank - it's a 6s (22.2V) battery, as specified by the kit producers. Bear in mind it's an EDF, so I presume the usual "Watts/lb" rules as used for prop-driven models don't apply. Certainly the model performs well, but vertical performance isn't unlimited.

John - yes, I'm inclined to agree and I would expect outages due to signal loss to be longer. I'm struggling to think what else it could be. Having been into electronics, amateur radio etc for many years, my soldering is generally OK I think, and I've checked the connections thoroughly.

The ESC is a Hobbywing 80A OPTO (as was the original I think).

[John Cole]

Tim: I'm not thinking of YOUR soldering!

Have you calibrated the ESC (easy on a Hobbywing)? I have had odd results before calibrating.

I assume you mean the Pentium / Fentium / Funfly version. This is supplied in Low timing. I believe that for EDFs this should be changed (easy with the card), but I have no EDF experience.

[Erfolg]

I am not sure there is necessarily a real problem.

Like many modellers my experiences are quite limited, down to my own equipment and observing others. I have about 16 ESC of various makes and models.

I think I have the same issue on one of my set ups, well similar. As the Lipo runs down, my motor cuts in and out, can give the impression of twitching. This is because this particular ESC is set to a voltage cut of point, rather than a gradual power reduction to the motor which I have adopted when ever possible on my other ESC's.

[John Cole]

Worth checking the cut-off setting, but "soft" is the default on HobbyWing ESCs.

[David E]

I don't think that signal loss would necessarily be for longer periods, which would be more typical of a receiver brownout. Can you post a photo of your receiver and satellite installation? Are either near the battery pack, ESC, or other metal objects? How far apart are they? Are the two receivers oriented with their antennas at 90degrees to the other receiver's antennas?

Is the receiver light flashing upon landing? (This would indicate Rx brownout during the flight, although disconnecting and reconnecting the Rx battery without power cycling the Tx will also cause it.)

It's a bit of a long shot, but could the ESC timing setting cause anything like this?

[Tim Kearsley]

Thanks for the theories chaps. The ESC has been left at factory defaults, which I believe means that it cutsppower to the motor gradually when low Voltage is detected. In my case, I've noticed the power glitvhes just seconds after take-off, with a fully-charged LiPo, so I don't believe that it's due to low Voltage.

 

I just did a short, very unscientific check on possible signal quality. I powered up the model (which was in the garage) and walked around the garden and in to the road with the Tx at normal power output (i.e. not "range testing" ) I then plugged a Spekky flight log into the data port. Results:

5.2V

999 fades on the internal Rx

68 fades on the external Rx

52 frame losses

1 hold

 

Now it's not a good test, as the model was in a brick building, but the fact that the signal was poor enough to result in a "hold" makes me wonder. At the furthest, the Tx was probably no more than 80 feet from the Rx. Also, the asymmetric nature of the result makes me think that the Rx may have a problem (it's a year or two old and has been in previous model(s)). If I understand it correctly, a "hold" implies a momentary loss of control.

 

I think my next action will be to swap out the Rx and flight-test again. I'll report back in due course, lest it is useful to anyone else in the future.

 

Edited By Tim Kearsley on 01/10/2012 20:23:40

Edited By Tim Kearsley on 01/10/2012 20:24:09

[Alwyn Gee]

Hi Tim

As you may remember I have this model too and so does a fellow club member. I've not had a chance to fly mine again since doing the mix you are talking about with the throttle and elevator but one thing you should know is, that buried in all the spagetti in the fuselage under the canopy is a switch from the Ubec to the receiver and this was the suspected cause of the demise of my club-mates model. He thinks that it had become partly switched off at some point whilst either trying to get all the wiring pushed into the space below the battery tray or just by pulling the wiring around when fitting the battery or maybe even just because it can float about loose in the compartment. He cut the switch off his replacement airframe and just taped up the wires as it is an open circuit switch so you must not tape the wires together. Having been pre-warned about this I simply taped round the switch on my model so that it cannot move. It would be a lot better if the switch had been mounted in the model so that it was accessible from outside to isolate the receiver to prevent accidental operation of the throttle. Not such a big issue on an EDF i know but still useful.

It would be worth making sure your switch is fully on and not able to be disturbed in flight.

Alwyn

[Frank Skilbeck]

Posted by Tim Kearsley on 01/10/2012 15:43:51:

Frank - it's a 6s (22.2V) battery, as specified by the kit producers. Bear in mind it's an EDF, so I presume the usual "Watts/lb" rules as used for prop-driven models don't apply. Certainly the model performs well, but vertical performance isn't unlimited.

Tim, OK, for info I flew my Top Gun Viper, 90mm EDF, which weighed just over 4lbs with 950w on a 4s, it didn't seem short on power once it was in the air, but yes you need more watts per lb with an EDF.

I flew this with a Spektrum Dx6i with an AR6200 Rx mounted in the cockpit along with the ESC and retract air bottle, no loss of radio control or glitches (just a reluctance to slow down for landing ) One other thing to check would be if you are getting adequate cooling to the ESC, if they get hot they can cut out.

[Alwyn Gee]

This is a 5lbs/2500g bird guys, I dont know where you're getting 3lbs from.

Alwyn

[Tim Kearsley]

Alwyn - my sincere apologies, goodness knows where I got a flying weight of 3 lb from!! You are absolutely correct of course, the spec is a weight of 2.5 kg (about 5.5 lb). So it comes in at around 300W/lb.

 

Regarding the switch attached to the UBEC, I cut that off from day 1!! I'm not a fan of switches as I think they are just another weak link in the chain. So I taped the individual wires as it is indeed a switch which is "ON" when open-circuit!

 

Frank, re cooling to the ESC, I don't think that should be a problem in this model, as the ESC sits directly underneath a slatted aperture in the underside of the fuselage and gets a decent airflow I think.

 

Edited By Tim Kearsley on 02/10/2012 07:35:23

[Frank Skilbeck]

Tim, from what you describe above and the flight log data it does sound as though it maybe radio problems, just to eliminate the TX have you flown other models with this since you had the issues, if not it maybe that the Tx has developed a fault.

Also you may want to repeat the test on the Rx with it out of the airframe and powered by a separate battery, if you get the same results then it's the Tx/Rx if not it points to an installation issue. The age of the Rx shouldn't make any difference unless it's been subjected to severe heat, vibration or arrivals. I've got several spekky Rx's which are 4 years old and they still work as well as the day I bought them.