Maiden flight crash

[david harrison 2]

went flying today, with a brand new sebart sukhoi s29 50e. The model was fitted with the factory Hacker A50 16s motor and Hacker s bec 70 pro .Battery was a thunder-power 6 cell 3850mah LI_PO. Servos are aileron JR8231 dig, rudder JR8411 dig, and elevator JR589 dig. A highly proficient friend was test flying this model very well for approx 4 minutes, then did a reasoably slow run-by on knife-edge. Then he did a snap-roll to opposite knife, when he informed me he had lost all control. The model carried on in knife and flew a perfect arrow-like trajectory into the ground and trashed itself. The receiver was a SPEKTRUM AR7000.

Can anyone tell me a possible cause. One person suggested bec got overloaded with all of these digital servos and the receiver dropped out thru low voltage, and by the time it has re-booted the model has gone in.By the way, when I got to the crashed model everything was still working OK. Can anyone PLEASE tell me if this is a plausible cause.

Thanks DAVE.

[Former Member]

[This posting has been removed]

[Tim Mackey]

Firstly, commiserations on the model

I cant find such an ESC listed. Do you mean Hacker X-70 SB Pro ? If you do...then my money is on a BEC failure due to overload, which would certainly mean an insufficient supply to the receiver.The reason I say this is the likely cause is because the BEC on that particular ESC is only rated at 3A MAX, and is I think, linear, not switched, and running that many DIGITAL servos AND a reasonably thirsty AR7000 receiver in a fairly large and aerobatic model is a disaster waiting to happen. Spektrum warn quite clearly about the test routine that should be applied to a model using a regulator to supply the radio - do you know what it is...and did you follow it ?

Of course, it could be pilot error , if not, and if my summation of the ESC etc is correct then its owner error, sorry

[David Ashby - Moderator]

Sorry to hear David. Does the SebArt manual say anthing about having a separate receiver battery pack? or separate BEC? It's an issue that manufacturers seem to ignore a lot at the moment. Some of the recent E-flite kits I've built do have a leaflet about this tucked in the box but they're the only ones that I've seen.

[scott cuppello]

I keep saying to people that Spektrum is being treated as foolproof....and it's far from it. Firstly, low voltage from the RX power supply will cause total lock-out with no warning. It's also important to check that BOTH RX light up when you switch on....I have found that's not always the case.....the gear is brilliant, but not foolproof.

As for BEC's, you may have noticed that a new generation of ESC's are popping up with "super" BEC's fitted, which I am just starting to use with caution. I have always worked on the basis that if you have any doubt about the BEC handling the set up.....listen to your instinct....on high power electric models [which is basically all I fly personally these days] I use a seperate RX power supply [nicad on heavier models, Lipo with voltage regulator or seperate UBEC on lighter stuff]....great, no reliability problems ever....provided you stay on top of the RX power supply charge! Sorry to hear about the model David.

[Alan B]

Sorry to hear about the model Dave irrespective of cause - damm shame!  Excuse my ignorance, if you are not fully up to speed on voltage supplies- BEC's - ESC's on electric aircraft and are flying with the manufacturers suggested power gear ie recommended motors, ESC's (with combined BEC's) , props and Lipo's. I fly using speckrum gear incidently - I have just put my Acromaster together and is ready to, then rule of thumb would be - if in doubt then always add a seperate power pack to power the RX independently.

concerned!

Thanks Al

[Michael Dearden]

Ooooo I know the feeling David - so sorry

Going back to basic electrics, a heavy current drain on any power supply will reduce its output voltage, by how much depends on its power rating. It is ALWAYS a good idea to have a separate receiver battery. That way, no matter what happens to the main powere supply, you will at least retain control.

Thinking back on things, I think this was a contributing factor to one of my Gemini crashes which happened "for no apparent reason"! It only takes a split second to lose all control, but several to regain it!

As they say, hind sight is 20/20

[Tim Mackey]

Yes and I keep saying that if your receiver locks out or fails in any way due to an insufficient power supply, then its NOT AN EQUIPMENT FAULT, its an operator fault. Any R/C receiver needs a n appropriate level of power to work, and if starved of such then expect a problem !

[Mouldy]

I run a Sebart Katana with 35mhz equipment installed.  Same ESC and Im using the internal BEC. This BEC is rated at up to 6 servos, (digital or otherwise, 2 being the minimum number to use), and the Katana is only running 4. I suspect that the Sukhoi is the same. I have no problems at all with this set up.

I believe the BEC supplies 5V to servo's/RX although Im not entierely sure of the current draw and cant find any detail of this on their site. Im also led to believe that the BEC in the Hacker SB series of ESC is above average in that is stable up to and including the use of 6S Lipos.

Sorry to here about the plane, but if you get another and insist on using 2.4gig then I would use a seperate RX battery. Alternatively stick to 35meg.

My ten penneth. 

[Tim Mackey]

Mouldy....which is the ESC actually, and do you have a web link to it? The description given in the opening post didnt seem to match any Hacker ones I found.

Incidentally, why would sticking to 35mhz have helped? 

[Tim Mackey]

I still cant find any Hacker ( made by Jeti actually anyway ) ESC with the description given

The only one I keep getting is X70 SB-PRO and according to THIS  the BEC is only rated to 3A ?? 

[Mouldy]

http://www.hacker-motor.com/deutsch/

Unfortunatly they dont do English!

My understanding of Specktrum gear is it locks out if the battery voltage drops below a given point. This point dosent seem very specific?

Ive never had this happen with 35! 

[scott cuppello]

This has happened to me bench testing retracts, once the RX power [regardless of what it is], the system locks out, you have very little warning.....not enough to get a model down in one piece....it's not a problem....as long as you treat the system with respect.

[Mouldy]

Agreed, but the point being is that 2.4 dosent seem to care much as to what voltage it cuts out at. The original post of this thread indicates that this was a maiden flight. Im also guessing that the battery would be fully charged. So unless it was a duff battery, (possible), then why would the RX lock out?

[Tim Mackey]

OK so it is the one I mentioned. The site I first found it on stated the BEC is only 3A capable, and the hacker site itself ( in deutsch ) syas 2- 6 servos - but I can not see where it says 6 digitals are OK!

However, at least it is a switching mode  BEC - but that is probably down to it being able to handle 6s LiPo rather than anything to do with its current capacity. Switch mode BECs are really the only way to drop such a large input voltage down to the required 5 or 6V. Unhelpfully, the site does NOT state the maximum current capacity of the BEC, and therefore I would be referring back to other site I linked to where t DOES state this limit, and its ONLY 3A ! These maximum BEC limits are often optimistic also, and in reality much above 2A could cause a problem, and I would suggest that on 4 x high power full size digital servos, this current could be easily exceeded.What reinforces this thinking even further is that the rudder servo is a whoppingly powerful ( 155 oz' !! ) brute, that has been measured on another forum as consuming 1.5A all by itself when under load !!

The original post said the model was in slow knife edge pass at the time of failure, so guess which servo was working hardest

Digitals take a lot more current than analogue. 

[scott cuppello]

Timbo hit's it on the head.....2.4ghz is brilliant.....for leccy fliers the best thing since sliced bread.....the point I'm trying to make is that if you don't treat the system with respect.....it will go wrong.

The USA have had them for quite some more time than us [Spektrum], and when it was launched here, people were hailing it as far more than it actually was.....the guys I know over there, quite rightly said;

"All it does is to stop glitching via equipment on the model, and stops another flyer shooting you down, after that, a radio is a radio"

And it's quite right, it will fail through low voltage [as will any 35mghz radio], it will fail through bad installation.....it will even glitch [even though it's highly unlikely] given the right circumstances [2.4ghz camera...been there.....reports of mobile phones in people's pockets...when you are flying...why?].....but all these things I'm afraid, as has been pointed out....are pilot error.

[david harrison 2]

Firstly, may I say I have been overwhelmed by the response to my original posting of "maiden flight crash". In reply to DAVID ASHBY, no there was no warnings in the kit. In reply to TIMBO, yes the esc is a HACKER X-70 SB PRO. As like most aeromodellers, I have a reasonable understanding of ELECTRICS but NOT of ELECTRONICS and their complexities. Getting back to my crashed model, I am NOT trying to blame SPEKTRUM or the makers of the model for the crash. I am trying to understand what may have happened, with a view to a possible future remedy. This model has set me in a sizeable chunk of change which I can ill afford, so a future re-occurence would really tick me off! The battery pack alone was £154 and is splattered on one end so possibly a write-off. Not bad for 5 minutes flying! Any way gripe over and time to move on. As I reasonably understand it, I guess I need a separate battery pack to power the receiver and servos. Considering the servos I am using, would a NI-CAD pack of around 1700mah be sufficient, also would a separate switch be needed? Also how do I actually plumb allthis together on the model, If anyone can help can they PLEASE explain it laymans terms as the intricacies of technical jargon go straight over my head. When it comes to the oily lumps up the front , then I know what is happening! The reason I went to 2.4Ghz was bacause my first 2 electric models went in on their initial flights. The first with 35fm PCM receiver, lock out and goodbye. The second I put down to me. This is my fourth electric model so I am becoming a bit paranoid about LEKKY. Cheers DAVE. 

[scott cuppello]

Hi Dave, ok, firstly, if you go Nicad, bear in mind the extra weight, I would have thought 1700mAh would be OK, I have warbirds running on 7 servo's [inlcuding digital & retract] on similar, without a problem. Needless to say, take this extra weight into account for C of G

You need the Nicad, a standard IC style RX switch harness, which will plug into the "battery/bind" on the RX, into the Nicad, with the charge lead dangling/tied up for charging.....so that's the RX/servo power taken care of. Now, ideally, you want an OPTO ESC, this will obviously control the motor....and nothing else, and plugs into the "throttle" channel, and to the Lipo as standard....and that is it basically.

If you intend to use a BEC ESC in this configuration, you MUST cut the red RX wire, and isolate it. Some people don't like doing this to BEC ESC's, and reccomend OPTO types in this configuration.

You now have RX power not dependant on electronics, and the added benefit of reduced signal noise [not much of a worry anyway on 2.4ghz] from the ESC.

OPTO ESC's will not arm until you switch the RX power on.....BEC ESC's, which have the power lead cut still want to act as before...and may arm as soon as the Lipo is connected....so be careful if you go down that route....an OPTO will just sit dumb until it get's an RX signal [but don't leave the Lipo connected all the time...it will still draw current].

Hope this helps?

[Tim Mackey]

Hi again Dave, and once again I am sure I speak for all - great pity about the "accident"

Now I don't want to point fingers - but have you absolutely eliminated pilot error ? Bit tricky this one I know...but we really are into a process of elimination here

Assuming you have....then consesus appears to be "radio failure due to insufficient power". One thing we haven't ascertained is whether you were on 6V or 4.8V from the BEC, again no information from the website, but I assume ( dangerous ) it was 5V which is the same as 4.8V really and is common for combo BECs. If it was 6V then it means apart from increased servo speed and torque, the whole lot is taking MORE current, compounding your problem of insufficient power available via the BEC. Not even ure that all those various servos are actually approved for 6V anyway.....

Now with that particular style of model, and the fact that you are using full size powerful and thirsty servos, I think I would be inclined toward a seperate battery. There are some good standalone BECs available, but many of them are designed for 2 cell LiPos and therefore you would need the extra battery anyway...so maybe just use a decent ( I reckon at least 3000m/a 4.8V nmh pack ) NmH pack.

Plumbing involves disconnecting the BEC power from your nice shiny ESC. The best way to do this is to lift the little tab on the servo style plug which goes to the throttle channel and remove the RED (or brown if JR style ) pin from the plug, tape it back against the cable, insulated and out of harms way. Leaving the other 2 pins in place maintains the very necessary negative rail to the receiver, and the signal which the receiver needs from the ESC to determine throttle position.

Now, use the battery as above to power up the receiver and servos by plugging it into the normal battery socket on the receiver, via normal switch harness. REMEMBER this battery will need charging and maintenance just as any other flight pack. Best practice is to switch this on BEFORE connecting main power pack to motor !

1700 mahr would do....but with batteries so cheap these days, and a model which will easily take the extra few ounces..... go for the bigger capacity. Just my .02P

[david harrison 2]

Once again, very many thanks SCOTT AND TIMBO for your very quick responses which are very informative. Can I possibly clear up a couple of more points then I will put all this to rest. Firstly is there any advantage of going to a 6volt receiver pack over 4.8v apart from quicker servo response. And if I did go 6v then presumably Iwould need a voltage regulator to keep the voltage at 6v or slightly under, as a fully charged 6v pack can hit probably 7.2v or more, which I believe a JR servo will not tolerate. If so, where do I get voltage regulator from. Also is there any technical advantage in useing  bec ESC over a OPTO ESC or vice-versa. Finally I can emphatically say this was NOT pilot error in any way shape or form. And totally finally! there are a couple of identically equipped models in my club. One of which is running the same aleron servos, similar elevator servo and a digital rudder servo of unknown power.We are both running a gizmo called a SCHULZE LIPO-DIMATIC 6, which is an onboard LI-PO monitor to make sure one cell in the LI-PO pack does not go below a preset voltage, in my case pre-set to pulse the throttle as a warning to land. This never kicked in. The ONLY difference between my model and his is I am on SPECTRUM 2.4GHZ (ar7000) and he is on 35FM useing aFUTABA 12MZ trannie and I believe a MULTIPLEX "IDP" RECEIVER,. He comes up every week and flies with never a problem and I don,t get it.

[Tim Mackey]

lots of things here Dave

6v over 4.8 - nah... just uses more juice as I said. The figure of 6v is nominal, but IF the servos are happy on 6V ( many JRs are NOT ) then just use a 5 cell pack instead of a 4. No regulator required.

OPTO ESCs have the advantage of completely isolating the ESC from the receiver, which for 35Mhz stuff is an advantage. If you use an opto esc you cannot deploy a BEC, and MUST use a sepeate pack to maintain isolation. Frankly I see little advantage when using 2.4Ghz.

I did an article on this subject somewhere...will try and find it Got it here ya go...

The LiPo guard you mention will only kick in IF any individual cell in the pack drops below the critical LV threshold...usually set to around 2.75V or so under load.

MPX IPD receiver are excellent 35Mhz rcvrs, but will not "lock out and require a reboot time" if they suffer a short duration voltage drop, probably not even notice it....but it may be happening to him as well.

[scott cuppello]

There have been problems with digital servo's on 6v, now, a full charged 4.8v Nicad pack will actually be more like 5.5v, and a fully charged 6v pack, more like 7.5v....which is what causes the problem. Cheaper end voltage regulators are only rated to around 3A! So, if you go down that route, get a good one.

People often ask me what servo's I'm using, because they seem fast .....and are suprised when I point out that most of them are £5 Futaba stockers and so on! The reason they are fast is that my Nicad pack is always full charged when I get to the field. Lack of voltage is either not charging them enough, or the pack running down quickly due to excessive current draw....hence a larger pack needed.

[david harrison 2]

Hi again SCOTT &TIMBO, Can I run one more idea up the pole. I,ve just been looking at various battery packs and the weight of some of them is getting a bit on the high side. How about a 2100mah 2S LI-PO pack running thru a POWERBOX SYSTEMS regulator rated at 5 amps and at 5.6 volts (linear), thats what the ad read. Is there any technical reason why this could not be used as this is amuch lighter set-up

[Tim Mackey]

OY ! you said you'd finished with the Qs !!

If you mean for the radio supply, then you wouldn't really need to go as high as 2100mah if you didnt want to, 1700 is fine, and is what I use in my IC Spit, but equally 2000 mahr is also fine if you dont mind the slight extra weight/size. If you have read the link I gave you, I have explained how using a higher input voltage on a reg, and getting lower output voltage is actually quite good for lowering your battery current needs.

Here's an extract from another thread I did ages ago, on just this subject.

If you are considering the powerbox regulator, then I have a rather favourite IC Spitfire which also uses high torque and digital servos, and I use a somewhat different system on this. It is called a powerbox digiswitch. Although basically still "just" a regulator in principle.....it does feature a clever integral digital switch ( which cannot be accidentally operated through vibration etc ) and an externaly mounted heatsink which allows a greater current flow, easily up to 5A from memory. Plus it has an inbuilt voltage monitor which indicates the level of your 2s LiPo pack, and will prevent switch on at all if the pack is considered too low. Although more expensive than a simple standalone BEC, I feel the extra features make it ideal for more "treasured or demanding" models. It is also very well built using excellent quality materials. Here is a link to the manufacturer.
http://www.modellbau-deutsch.com/e/powerbox_systeme/digi_switch/start.php

Other more elaborate versions are also available with even greater current capability. I hooked a DVM inline with my supplying pack, and physically moved the control surfaces ( several at a time ) to induce force feedback into the servos, and also moved the sticks to full deflection with hand pressure applied to the surfaces to check the typical current drawn in the worst case scenarios. I only ever recorded a peak of around 4A, but it might be advisable to do something similar. I have heard tales of extrememly high currents being drawn through some models systems....over 10A in one case!
PS AL's hobbies are also distributors for these items, so if you dont fancy buying direct like I did, then give Al a try.

[Tony Benton]

do you know during the flight was the areal on the spectrum pointing streight up or was it pointing  out the same as a 35 hrz controller would if areal was out its poss that the signal was lost as you need to point your areal at a 90 degree angle to your controller and should always make sure that it does not point directly at your model if it does in some cases this can mean a loss of signal being recived by your model 2.4 ghz systems operate in what i can only describe as a donut type signal  so if you point your areal straight at you model there is a possability that you will lose signal and crash as one of my friends at our club did he has since had no problems with his spectrum as he always makes sure that his areal is in a 90 degree angle to his controller hope this helps a bit if you wosh to test this out just go on low power setting and test it up to 30 paces with areal pointing streight at you model  hope this helps