Catastrophe!

[Nigel R]

They're almost all "cheap chinese ESCs" gangster, very little of this nature is made in Europe or USA.

60A with 80A burst, should cope no problem with a loop's worth of full throttle at low to mid 50 A.

Even on the bench - where a problematic install leading to cooling issues will not be affecting things - it is exhibiting the same odd behaviour. And quite repeatedly, if I understand Jonathan's post correctly.

I'm really struggling to see the failure mode in the ESC that could cause this throttle latching. For it to continually run at full throttle, it has to see a full throttle signal, continuously, at the signal input, which indicates the RX is putting out that full throttle signal.

Which suggests, not a BEC or power issue after all.

More digging needed to really figure the problem.

edit: correction to earlier post, I am not using an XP 60A, my father has and for quite some time, I have briefly but the ESC I am using in the install I was thinking of is actually a Hobbywing 60A.

Edited By Nigel R on 28/01/2019 10:24:04

[Chris Walby]

IMHO

The first "throttle" issue can only be either the ESC or RX to latch at full speed or continue to send full speed signal. Its odd that in both situations I won't expect the throttle cut to work as once "locked up" why would it unlock.

Second issue with the servos seems a power supply problem to the RX or the RX. If the supply dropped caused by the servos then the RX will restart (taking its time), but you would reproduce this on the bench.

Try a different RX and ESC an see if the fault goes/comes back.

Good luck and keep hunting for the issue

[Don Fry]

OK, I'm going to have a go. Now I know next to nothing about modern electronics, little about electric flight, and indeed little about radio control systems apart from long use.

But I have had formal training in problem and logic analysis.

Now, I can't think of any reason why, an esc will put out full power, ignoring the throttle stick, and then cut power when the throttle cut switch told it to. It's contact with the word is down the signal wire from the receiver. Therefore the problem is upstream, receiver or transmitter of that signal wire.

A partial and interesting test is to rebind the bits to a new memory on the transmitter. Then we lose all the funny old memory idiosyncrasies. Does the fault repeat in the new memory.

And why think it's a power supply problem, if lack of power shuts the receiver, failsafe cuts power, or if reversed leaves it on full, but if the receiver is down, then throttle cut won't work.

But be very careful. One broken model annoys. Two scars the soul, if caused by the same fault. As I once found out.

[Peter Beeney]

Certainly an excellent test report on the errant ESC, Jon, very thorough and concise indeed! It really does point to this as being the hobgoblin that gave you the grief. I’d say you are not really too much of a stranger to this electrikity stuff in general anyway.
One other little trick I might be tempted to try would be to re-bind another model to that memory and test them both in unison. That would prove the conditions irrevocably one way or the other, but now I’d be very surprised if it wasn’t exactly as you describe.

I’d guess that when the throttle stick is it’s top position the speed control pulse width signal is cut off completely. The same may also apply when the cut-off switch is operated. It seems the ESC does’t properly recognise a change from this for some reason; but you did say that it had been ok previously so now the other little factor in play is that you'd reprogrammed it immediately beforehand. So is it worth going back and having another look at this to see if you can spot any abnormalities that have now crept in here. Difficult to think what, but you never know… …otherwise it’s very coincidental again.

Overall though, it might really be a dodgy unit, If it does prove to be hope you can get some compensation. I think if you payed with a credit card that may be one avenue to look at if necessary. It’s certainly been done before.

Gook luck.

PB

[Martin Harris - Moderator]

Did you ever confirm the failsafe behaviour? I don't know your radio but could you have been in failsafe for a short period initially and the response to the cut off switch may have been coincidental? The loop could well have continued under failsafe holding the elevator deflection.

Could the throttle lead have been intermittent in the receiver port? Was the lead tight? I once carefully laced the servo leads on a model into a neat cable form and had one aileron servo stop responding during a roll - at full deflection! Luckily, I managed to land after a few fraught seconds while I established that level flight was possible with almost full opposite aileron and a large elevator deflection. Quite frankly, had the model gone in and I had not seen the frozen aileron I would have had little hesitation in putting it down to a massive glitch.

Examining the connections revealed that the mass of the bundled cables had pulled the shortest lead loose from the receiver under the rotational G load...

[Jonathan M]

I've finally solved the throttle problem! There remains the problem of loss of all control during the later spin manoeuvre, and there's also the annoying problem of the slow servos. But first the throttle problem, for which I went through a number of discrete steps in an attempt to keep the process logical.

The Throttle Problem

The steps: first eliminated the model memory (made a new model on the TX and bound this to the RX), then eliminated the transmitter itself (checked this on an old E-Flite park-flyer), then was left with the ESC itself (using the RX from the park-flyer), until I finally realised that I needed to do a global re-set of the ESC (rather than just re-confirming the individual settings by working through the menu-tree of beeps). When I did this with the park-flyer's RX connected up to the ESC, the problem disappeared completely and the maximum draw at full throttle-stick was 47A. When I repeated this global re-set with the original RX connected up and also re-calibrated the ESC to the throttle-stick on the TX, then not only did the problem remain gone, but the max draw increased to between 61 and 67A.

I then realised what had caused the problem in the first place! When very originally first binding my TX to the RX, I had made the error of not properly calibrating the ESC to the throttle stick. Having only previously had two electric RTFs I had never needed to calibrate their throttles (this wasn't necessary as I recall, and certainly wasn't necessary when binding my current TX to the old park-flyer this evening). Having more recently been flying IC with a throttle-servo, I thought I could overcome the lack of power at full throttle-stick by increasing top level sub-trim (I'd previously needed 70% throttle just to maintain level flight) , and reduce the excess of power at bottom stick by tweaking that sub-trim, etc.

None of this was a problem with the first dozen flights, but on the day of the crash last week, just before going up to the patch, I'd decided to check the individual settings (soft-start, correct battery-type, etc) by going through the beeping menu-tree. For reasons that are beyond me, although I didn't in fact change anything but just reconfirmed the settings and didn't alter the throttle sub-trims, in flight the ESC didn't like letting go of full-throttle any more.

Hope this all makes sense! But also, notwithstanding that I've corrected the problem by doing the global re-set and proper re-calibration of the ESC to the stick, and with no messing with sub-trims - and having learnt some very BIG lessons - I'm going to put this ESC (£22) straight into the rubbish bin.

My replacement Wot4 will have a more expensive ESC from 4-Max, and for good measure I'll be powering the RX with a separate 2000mAh NiMh.

The Fatal Loss of Control Response During The Spin.

Unless the loss of control during the spin was somehow connected with the specific ESC problem explored above (but I can't see how this could happen), then the culprit comes down to the Spektrum AR610 receiver (from a regular well-known RC online supplier so I assume not a copy), a poor connection somewhere, or interference of some sort. It might be that the RX is not at fault, but I cannot rely upon this, so that too is going in the bin (£36). The interesting thing about the AR610 is that (unlike the little old park-flyer's AR6115e) it doesn't possess the slow-flashing red light that indicates a brownout. There's also no way I can test now for any connection issues, nor can I easily determine interference.

Servos

I've tested my set of New Power XL-38HMB servos using different receivers and different battery types, etc and - torquey as they may be - they are unbelievably slow!!! I used a stopwatch to repeatedly time ten cycles of full stick one way then the other (60° travel) and the time for full movement was about 0.6 or 0.7sec!! They are advertised as 0.14sec at 6.0v and 0.16sec at 4.8v and are patently NOTHING EVEN REMOTELY CLOSE TO THAT!

I'll definitely be contacting the retailer for a refund!

Thanks so much for bearing with me on this one folks. Its been a big learning-curve, not least the importance of grounding a model at the very first sign of trouble and keeping it there until the problem is fully resolved!  The loss of any control during the spin remains a mystery and might have occurred at some random stage anyway, but I'm hopefully the wiser for having gone through all this.

Thanks for all the contributions and suggestions!

Jon 

PS The replacement Wot4 arrived from 4-Max (not the original supplier) today.  It has a slightly smaller and lighter 35 sized motor and the dearer ESC.  The lighter motor, combined with a separate NiMh for the RX positioned under the wings, should help me get the CG properly back - as I really need to get that spinning manoeuvre properly sorted....!

Edited By Jonathan M on 28/01/2019 21:01:39

[Nigel R]

I wouldn't be so hasty to bin the ESC and RX.

As you don't yet know what caused the loss of control crash, it could also be the TX, any wires you may have used, the battery in the TX, some interference. And you're not throwing the TX, I presume?

Your control loss in a spin (with throttle closed anyway) could have easily been the default failsafe behaviour. Occasionally, 2.4GHz does have signal problems, it is not 100% immune. I would put that as more likely than an RX build issue. I think you need a flightlog or telemetry module to show if the AR610 recorded a brown out or frame loss (interference).

Perhaps worth asking about the RX install. Was the aerial aligned with any carbon or metal pushrods? Has the RX ever experienced any physical trauma in the past, is there any cause to suspect its aerial is damaged?

Personally, I would put the RX on foamie / parkflyer duty for a good long stint. The ESC I would at least keep for bench test duties. No sense cutting your nose off.

All of which leaves aside that it's good work to nail down the subtrim and incorrect setup of the ESC as the cause of the sticky throttle. That's just a lesson to learn for the future - always set up the ESC... and don't ever mess with subtrims on electric - there is no point and it serves only to drive the ESC incorrectly.

I note the overlander instructions do actually tell you to do the throttle range on first use.

Lastly, I also note the overlander instructions look remarkably like the ZTW instructions I received with a Beatles 50A ESC. Apologies for misinformation earlier where I stated I thought Overlander were rebadged Hobbywing.

[Former Member]

[This posting has been removed]

[Jonathan M]

Nigel, good questions about the RX and its installation!

It was brand new, but it was mounted on the balsa floor of the Wot4 in a fairly restricted position about 2/3rds back from wing LE, with the R&E servos in their tray just above it. Other than the servos themselves (Sullivan snake for the elevator and pull-wire for the rudder, both running aft away from the RX) there was no other metal nor any carbon, but there was some bunching of wiring (the R&E servo leads and the extension leads from the aileron servos) in the general boxed-in area of the RX. The LiPo and ESC were of course well forward

Thinking about this some more... the RX wasn't exactly in an optimum position down there on the floor with its short antennae potentially shielded from the signal, especially during a spin or rapidly spiralling dive!

On the practical front, it was also a right fiddle to get to. So for the replacement Wot4 I'm inclined to mount the RX on the side wall higher up towards the wing seat and maybe a bit further forward away from the servo-tray and any concentration of wires.

---

Whether or not I keep the old RX for anything less valuable, I do wish to equip the new Wot4 with a new RX, but the question is which one? A Spektrum unit with a smart failsafe (one which doesn't just kill throttle like the AR610 which but returns control-surfaces to individually pre-set positions: level ailerons, slight rudder and very slight up-elevator) would have perhaps saved the model completely or at least resulted in less catastrophic damage.

However, I am in fact getting a Taranis 9X for my glider stuff (slope and thermal), the original plan being to keep the Spektrum for the two or three power models I have, but I wonder whether I might just sell the DX7 and all servos and re-equip the power models with FrSky...?

Any opinions on this?

Jon

[Ron Gray]

No matter what failsafe settings you have in place if it was a power failure then they wouldn’t have taken effect. I know that to my cost on my GP Revolver mentioned before.

Whilst I am a FrSky advocate I wouldn’t suggest getting rid of Spektrum just because of this event. However, if you only have 2 or 3 models on the Spektrum then consolidating on one system does make sense, the cash you get for the Spektrum would pay for the FrSky RXs.

[Martin Harris - Moderator]

Posted by Jonathan M on 29/01/2019 13:05:05:

Thinking about this some more... the RX wasn't exactly in an optimum position down there on the floor with its short antennae potentially shielded from the signal, especially during a spin or rapidly spiralling dive!

...seems to preclude blanking IMO - with rapidly changing orientation plenty of correct data packets should have got through.

[Jonathan M]

Cheers Ron - I'll first see how I get on with the Taranis with my gliders, then maybe migrate to the power models in due course.

Re the NP servos, I've spoken to the retailer and explained their geological-time slowness. They've asked me to post them back for examination etc. On the assumption that they're happy to refund, this will pay for a fresh 4s LiPo to replace the damaged one.

I need a new set for the replacement Wot4. I've got Futaba S3001 servos (specified at 4.1kg 0.22s) in my IC Acrowot which I've been very happy with; these cost £11.50 each. Would there be any merit (increased torque, speed or longevity) in spending nearly double on S3010 servos (6.4kg 0.16s)?

[Bruce Collinson]

Jonathan,

You deserve credit for the thorough and frank investigation and conclusion, some of which lost me a bit, but much of which resonates.

My current Wot 4 artf electric has survived for about 2 seasons, latterly with a Ripmax motor, Yeti ESC and Spektrum rx.. After the last surgery I replaced the rattly motor with a slightly larger Overlander which has yet to be flown; too cold. Never had a bad setup from 4Max so go for it.

Rx; mine is a simplish one, 2 antennae, just ahead of the servos, behind the LiPo which is a 5A 4S so fairly hefty. Never had a glitch. If replacing it I would be very tempted by the new hidden antenna Spektrum upon which there's a post on here recently with generally positive hands-on reports, as opposed to the hands-off Spekky hysteria which breaks out regularly.

Not a fan of New Power servos. Apart from anything else the servo arms are excessively thick. Got some Hyperion minis for a specific project, seem Ok but otherwise I'm keeping faith with Hitec and especially Savox which seem to me to be the optimum compromise of cost, performance and quality for anything I have built/assembled apart from combat wings and the like. Probably, those Futabas are every bit good enough for a Wotty.

Based on 100-odd flights I'm with Martin but they do seem to be a bit sensitive to aerial orientation, rather than location, as far as I can determine. I am happier with a satellite especially if it will go in a wing eg.

BTC

[Nigel R]

"The red LED flashing on the receivers that have it indicates holds (failsafes)"

I'm not sure the AR400 or AR610 do this, I could see no mention of it in the manual.

From mid range, the older 6210, newer 6600T and up, on the other hand, do.

They also do fancier failsafe, if memory serves me right.

"Would there be any merit (increased torque, speed or longevity) in spending nearly double on S3010 servos (6.4kg 0.16s)?"

Not for a Wot 4, no. Massive torque and/or speed just isn't required for 40 class sport models. Different considerations apply for a similar size 3d model, or a 60 or 20cc sport model. But a Wot 4, no, it is amply served by "standard" kit. Remember also that higher torque comes not for free and pokier servos also need a bigger power source; a standard 5A SBEC or 4 cell AA might not be beefy enough to cover them under a 'worst case' scenarios. Same applies to most digitals.

Standard Futabas 3001 are nicely made, and have good centering and resolution. A well proven bit of kit and a good choice.

Hitec 425 (or whatever the number is for the standard size ball race one) would also be a good choice - I tend to go with Hitec in the main. I might put a 475 or 485 on rudder duty, if you plan on flying consecutive knife edge loops.

Savox also get rated, though I am not a user and don't know the model numbers.

[Jonathan M]

Posted by Nigel R on 29/01/2019 14:11:22:

Massive torque and/or speed just isn't required for 40 class sport models. Different considerations apply for a similar size 3d model, or a 60 or 20cc sport model. But a Wot 4, no, it is amply served by "standard" kit. Remember also that higher torque comes not for free and pokier servos also need a bigger power source; a standard 5A SBEC or 4 cell AA might not be beefy enough to cover them under a 'worst case' scenarios. Same applies to most digitals.

Standard Futabas 3001 are nicely made, and have good centering and resolution. A well proven bit of kit and a good choice.

Thanks for that Nigel... however I don't think I'll be doing "consecutive knife-edge loops" for a while yet!

Re a new receiver, just looked up the manual for the new internal-antenna AR620, which does have pre-set failsafe, whereas the AR610 (my current receiver) doesn't. The 6600T also has it but is twice the money and I don't really need telemetry.

But - going back to what could have caused or contributed to the loss of control in the spin - the New Power Servos DO have massive torque, rated in the literature at 11kg! Could it be that with all four servos at their extreme to enter and hold the spin attempt, this proved too much for the 5.5A BEC to RX power-supply... and contributed to signal-loss?!

[Nigel R]

You reported yourself that there was a 2.25A draw with all four servos "going bananas" - although you didn't state the physical load on each servo, or if there were no loads.

A test very much worth doing, is, if you hang the nominal rated load, 11kg at one cm, or 10lb at one inch, what does that do to the current draw when the servo operates? The servo(s) may also be faulty. You have already reported very slow operation from what, at 0.16s/60deg, should be a fast servo.

Either way that bench test would certainly rule out (or point the finger) at the total power demand exceeding the BEC's capability, and thus causing a brownout.

Must admit, this is one reason I have simply not bothered getting any digital servos - the unfashionable old analogue servos do not place much demand on their power systems.

[Jonathan M]

Good point Nigel. The 2.25A max draw was recorded on the watt-meter while I was repeatedly going 'bananas' with the TX sticks but with no actual loads on the servos and motor not running. As referred to previously, I also did individual static tests on each servo, travels set on the TX to 100/100 so 60° on the servo, hanging a bag containing 0.815kg of lead from a clevis in the same 3rd hole out of each servo for consistency, and driving each stick in turn from one end to the other.

	Watts	RX volts	Amps
elev	3.8	5.50	0.69
rudd	4.2	5.50	0.76
l-aile	5.4	5.50	0.98
r-aile	6.2	5.50	1.13
TOTAL	19.60		3.56
AVERAGE	4.9		0.89

From this the average draw on each servo was 0.89A, but a total of 3.56A together! However I have absolutely no idea what the current load from each servo would have been during the spiral-dive with the surfaces deflected - almost a kilo each or much less or much more?

BUT I'm now moving on - especially as I've got a lot of day-job work to catch up one!. Had to go to town earlier to see the accountant, so posted the servos back to the retailer with the request that they test the servos themselves for speed and give me a refund or credit note. I'm not in a position to argue for any more refund (i.e. the model itself) as there can be no conclusive blame for the crash on the servos. The main thing for me is that I've learnt an incredible amount more about EP, ESCs, RXs, servos, and prudent operation of a model aeroplane - both from the catastrophe itself and from the many really helpful contributions to this thread. I'm now looking forward to getting the new Wot4 assembled ready to take back to the air as soon as the weather improves.

One thing that will be interesting to then see is how the Wot4 flies with the new 35 size motor from 4-Max on the same 4250mAh batts - compared to the Overlander 40 motor as originally fitted - and any difference in flight duration. If the 35 turns out to be a bit too weedy for my needs (unlikely as I like 'moderate' and this is what George recommends anyway) then I can always swap back in the 40 (with a new ESC rated for that).

[Nigel R]

Hmm. That is some variation between those servos. Also, that 0.8kg, at about 1" out? represents around 1/5 of the rated maximum. So in extremis, I can see the combined load of the four digitals easily being too much for the BEC.

You're taking it very well - treating it as "every day's a school day" is the best thing to do.

I would stick by my earlier suggestion - put the RX on a parkflyer to prove it, and keep the ESC for bench duty.

Whatever you do, enjoy the next Wot 4!

[Bruce Collinson]

PS reinforce the u/c plate before assembly. Far easier now than later.

BTC

[Ron Gray]

Just a couple of things about my Wotty. I too am using New Power servos but only for the rudder and elevators, I've got Hitecs on the ailerons. Having said that, I've not had any problems with the New Power ones and their speed seems to be ok. The C of G is about 98mm back from the LE (instructions say 82mm). I checked the C of G using various flying methods and with it in this position it only needs slight stick pressure for inverted flight. However I have adjusted the tailplane incidence, raising the TE by about 3mm and in vertical, power off dives there is now no pulling to canopy or U/C so spot on. All this has meant that it does all aeros quite nicely including rudder / elevator spins in fact if you feed in a bit of ailerons the spins are manic! Anyway here are some pics to show where the battery is located (5s 3000) and the raised elevator TE.

[Jonathan M]

Posted by Bruce Collinson on 29/01/2019 19:17:26:

PS reinforce the u/c plate before assembly. Far easier now than later.

I'm a fan of 5mm nylon bolts for the U/C for both my Acrowot and the Wot4. I learnt that lesson early on with the AW when a mahoosive mole-hill reared up on a dead-stick landing and ripped the U/C off together with the supplied metal bolts and the bottom front of the fuselage! The same happened with the first Mrs Wot4 when I just missed the runway in gusty conditions and came down the in the rough before I could regain airspeed - two minutes later I had the nylon stubs out and the U/C back in place with new bolts. So I'll deffo be doing the same with the second Mrs Wot4.

[Jonathan M]

Posted by Ron Gray on 29/01/2019 20:42:49:

Just a couple of things about my Wotty. I too am using New Power servos but only for the rudder and elevators, I've got Hitecs on the ailerons. Having said that, I've not had any problems with the New Power ones and their speed seems to be ok.

Weird... I wonder what happened to my NP servos then?

The C of G is about 98mm back from the LE (instructions say 82mm). I checked the C of G using various flying methods and with it in this position it only needs slight stick pressure for inverted flight. However I have adjusted the tailplane incidence, raising the TE by about 3mm and in vertical, power off dives there is now no pulling to canopy or U/C so spot on. All this has meant that it does all aeros quite nicely including rudder / elevator spins in fact if you feed in a bit of ailerons the spins are manic! Anyway here are some pics to show where the battery is located (5s 3000) and the raised elevator TE.

Wow, that's a huge difference, a full 16mm further back than the specified point! No wonder I couldn't get the First Mrs Wot4 to spin properly with just rudder and elevator (at 85mm the old CG was a bit further back than spec but still a nose-heavy with a smidge still of up-elevator, at which also she seemed to need to fly quite fast to maintain S&L flight).

One thing I'm going to do before gluing anything in place on the 2nd MrsW4 is put an incidence meter (now on order via eBay US) on the wing and tail-plane.

A question about engine thrust-lines: my Acrowot IC has a built-in offset for right-thrust, but the EP Wotty doesn't have any allowance for that. Surely for proper aerobatics one wants to determine the correct amount of both side- and down-thrust?

[Ron Gray]

I suggest not worrying too much about various settings until you fly it. Get the C of G roughly as the instructions then fly it as that is the only real way of knowing if it is correct. Similarly engine thrust, mine hasn’t got any different from that built in but fly it and see and then make changes accordingly. The problem I had which was why I adjusted the incidence, was that despite the C of G being correct it would drop its nose when flying level, irrespective of engine power, that is why I did the power off vertical dive. I tried changing the wing incidence but found I needed less adjusting if I did it to the tail.

There are still some tweaks I will be making but for 90% of the time it is now how I want it. I’m also going to see what it’s like with a 6s and smaller prop, the one on their at the moment is a 16x6.

[Tim Cheal]

Jonathon

I am sorry for the loss of the Wot 4, but what a great thread, and great to see the analysis and investigation.

I end up with more of a question really, but what happens to the load on your set up when the servos are resisted in movement. Here is what I am thinking......

At full deflection (as per the spin) do (did?) any of the control services get to full deflection, and thus the servo is now pushing against an irresistable force? In this case, what would happen to the current on the servo? I'm thinking that the amperage may go up even higher than your table indicates, potentially causing a brown out. This would potentially happen only when holding full deflections, as you were using in the spin.

It may be the case that the amperage does not increase, hence my question which one of the electronic experts may be able to consider.

Thanks for a great thread though. (And I cant help thinking that BEB would have loved this thread!)

Tim

[Nigel R]

Tim, if you mean the control surfaces were starting to bind, then the servo could (I surmise, anyway) go right up to maximum (i.e. stall) torque which would indeed draw more current than Jon listed in the table. His current was measured at a torque of around 2lb/in, which is only 1/5 of the servo's rated maximum.

If the relationship between current and torque is linear (however I'm not certain that it is, we need an expert on electric motor characteristics here) that could mean, as the highest reading above was around 1A, that each servo could be drawing up to 5A when stalled.

Edit: worth noting that similar torque Hitec digitals (5645), have a manufacturer quoted stall current of 2.5A. This might be a more realistic figure to use in this case; in which case four of these could put a 10A drain on the 5A BEC, - woefully overloaded.  The standard size & torque Hitec digitals (5485) list 1.2A stall current, and four of those (4.8A) would be OK for the 5A BEC.

Edited By Nigel R on 30/01/2019 11:05:39