Cor I nearly crashed again

[Erfolg]

I was flying my model glider today, all seemed well on the first flight.

 

As I had not flattened the battery, I later decided to fly again.

 

This time on launch, the motor seemed to cut out intermittently on the climb out.

 

Having reached a reasonable height, I cut the motor, cruised a little, finding no lift, I wanted more height to search for a thermal, so switched on the motor. Shortly after switching on the motor, it seemed the motor was not running, at that point the model rolled on its back, dived vertically for about 200 feet.

 

 

No amount of stick waggling did anything, until about 50-75 foot above the ground, then the model responded, pulling out of its vertical dive. I slowly, so it seemed regained control, and brought it back to the field,tentatively turned into a landing pattern, and landed long. I dare not try and go round in case the model stopped responding, nor try the motor.

 

On landing, I ran the motor, which seemed to have bags of power, for a few minutes. At this point a member produced a battery checker, which indicated 18% full. I forget the volts shown.

 

Whilst returning home I began to think perhaps, switching on the motor dragged the volts down to a level that my Rx stopped functioning for a short period, when the volts recovered in the battery, perhaps the Rx responded.

 

I then thought what motor voltage cut of should I use to ensure that the Rx continues to function?

 

Of course I could be wrong what the issue is, yet i have had a number of issues since re-motoring the model. All of which I had put down to interference.

[Tom Wright 2]

35 OR 2.4 ?

A t 18% you should have been ok unless one cell is in a bad way.

 

TW2

Edited By tom wright 2 on 27/04/2011 20:09:09

[Erfolg]

In this instance, I was flying on 35.

 

Does not the voltage sag from a battery if you are pulling a heavy current?

[Tom Wright 2]

Hi Erfolg.Sorry my last post was rushed ,evening meal was on the table !

It sounds like you had an interesting problem,35 and EP does make me a bit nervous ,but it was not necessarily the problem. Lets start with the battery what was the make ,capacity and C rating?

 

TW2.

[PatMc]

What type of battery - lipo or nickel & were you using BEC ?

Sounds like you may have reached LVC & the intermittent motor running was the battery recovering & promptly dropping when the load's back on. Loss of control could have been that the battery was close to exhausted but recovered a bit on the way down.

These % battery checkers are misleading. IMO they're a complete a waste of money.

[Tom Wright 2]

Pat .

I have found batt checkers do give a reliable guide to safe power remaining,but not if the battery is a low C cheapy or near the end of its useful life.Lets wait and see what he was using and the recharge results.

TW2.

[Tom Wright 2]

Erflog.

Was the motor actually cutting out or surging ?are sure the tx and rx aerials were fully extended? Have you been flying the model with the same power train for some time?

At this point it does seem that the batt sagged enough to cause the problem,if so it could suggest that the batt C is very depleted at the indicated percentage remaining.try a better batt and check all plugs sockets and joints , then bench test the system,and do a range check before flying again,hope this helps unless you have found something else in the mean time .

 

TW2.

[Erfolg]

The battery is a 1550 Rhino (Lipo), 20c, pullng246 watts static. The speed controller is a AE series 40 amp Turnigy with BEC

 

On the second launch, I think the motor was cutting out. Another flyer, who the model passed by, as it climb out, said it sounded like a clunk.

 

 

The surprising thing to me, is how long there was no control. To put the model into a truly vertical dive, would in my opinion require the model to stall, in a massive way. The model then continued truly vertical for a good number of seconds, revolving slowly as it dived.

 

AS far as I was concened the model was going to crash, it was so enevitable, as the time passed. I was pulling up I assume, and probably trying to stop the rotation. Nothing was doing, I had sufficiet time to assess if the model was over the field or over the woods, and considered the issues of a retrieval from the trees. I then got some response, I do not think it was a solid response, as the pull out was somewhat tentative and slow. Once level and heading towards me, my confidence did grow, yet I feared that the radio link was less than solid. Hence my decision to land some 29-30 feet from me.

 

 

The battery check was less than ideal, as it was an afterthought, and also I did not have the presence of mind to check servo response on running the motor on the ground.

 

It was perhaps worth noting that the battery was very hot after all of this.

[PatMc]

Best take a note of what the battery voltage is now & how much charge it takes to assess what was actually left in.

[Simon Chaddock]

Erflog

At 246W static you are working the 1550 quite hard giving a full power duration of just under 4 minutes. The hot battery would seem to confirm this.

 

I would suggest that on the second flight you momentarily pulled the battery voltage down so low that the BEC stopped. This could well cause the servos to 'twitch' moving the control surfaces a bit, hence the dive.

Even when the battery voltage recovered the ESC would have to reset and in a vertical decent even a couple of seconds is a very long time!

If this is what happened the very low voltage state may also have damaged the battery.

 

How many times have you used the battery? They do degrade with use, both in C rating and capacity and the harder your set up works the battery the quicker you will notice any degradation.

 

Two flights on one charge? You may not be so lucky next time!

 

[Tom Wright 2]

Simon's comments on battery age/ usage may be a clue as a degraded battery can get very hot quickly when you try and drag the last bit of power,it is possible that a new battery under the same conditions would have been OK.It does sound that the power train is working flat out to achieve the climb rate you require ,what is the wing span and loading? My 4m span thermal glider will climb to 500ft at a 45 degree angle of climb and not even warm up a 2A 3 cell and i get at least four climb outs without taking the battery any were near cut off,so i have to assume your glider has a higher wing loading,requiring more power and perhaps a larger or newer battery? of course all this is assuming the ESC is fully serviceable

I suppose the easy answer would have been to try the system on returning home and before charging the battery open the throttle and monitor the bec output voltage .

 

TW2.

 

 

[Erfolg]

The model is a Saggitta, the first model in the foreground

 

The age of the lipo is approx 6 months.

 

Size is 2m.

 

Motor is 480L link

 

The climb out was a stop start affair, as I could not find lift, only the sink. That is till a Buzzard appeared about 10m from my model, in lift, same height. I joined it, when I climbed strongly. A few minutes later I was scratching for lift again.

 

I think I started the motor to climb, possibly 10-30s later, the model rolled into the vertical dive, on reflection, that is how I now think the vertical dive started. Yet with many things with respect to memory, I am not sure of these initial events, as all was so ordinary. Once n the dive my memory is much clearer.

 

 

I have not attempted to charge the battery yet, as I have other things to do, more important.

[leccyflyer]

How many servos are you using and how many servos is the BEC rated for?

 

It does sound like you might have run the battery down to such a state that the voltage was depressed below that required by the receiver, during that motor run.

[Erfolg]

The ESC is a Blue Series 40amp ESC.

 

Two servo are used Park L , which I think are these, though purchased in the UK for about £12 each.

 

Wing loading is about 10oz pe foot square

Edited By Erfolg on 28/04/2011 10:49:05

[Tim Mackey]

I must say I am a bit skeptical about the suggestions.

To run a 3s LiPo ( I assuming its 3s as I couldnt actually see confirmation of that ) so low as to be unable to feed a BEC with the minimum input needed to supply its 5V output means its very very low indeed.

If the regulator is an LDO design ( low drop out ) device then the DO voltage differential is probably only 1V or so.

This means your pack had to be down to 6 -7 V or so.

Thats 2V per cell so its likely goosed it anyway. Or WAS it a 2cell perhaps?

Maybe the BEC ( or something else in the supply chain to it ) failed

[leccyflyer]

I think the point being made is that the extra motor run, with the battery voltage aready low - it was only reading 18% left at the end of the flight (though a record of the actual voltage would be more useful) - may have been sufficient to drop the pack voltage down to a level insufficient to sustain the receiver. That would only need to be a momentary drop of the pack, under heavy load, to less than the required input voltage for the RX.

[Erfolg]

I am using a 3s the battery!

 

Timbo

 

Being really open, I really do not know what happened, other than the loss of control was prolonged, unexpected and the duration so long as to contemplate that the model being over 20 years old had a good run for its money, the second thought was about where it would impact and would I be able to retrieve some of the gear.

 

I was really surprised when it started to respond, I was then fearful it would stop functioning again. I was really tentative about touching controls and the approach path, not just in case, but because I thought disaster was imminent.

 

My own thoughts have tended towards, have I set the programming card properly or sensibly. This is the one I Blue Card use.

Edited By Erfolg on 28/04/2011 11:38:57

[Tim Mackey]

Posted by leccyflyer on 28/04/2011 11:26:29:
I think the point being made is that the extra motor run, with the battery voltage aready low - it was only reading 18% left at the end of the flight (though a record of the actual voltage would be more useful) - may have been sufficient to drop the pack voltage down to a level insufficient to sustain the receiver. That would only need to be a momentary drop of the pack, under heavy load, to less than the required input voltage for the RX.

 

Its actually a little worse than that TBH. The receiver ( and servos to some extent ) will probably be OK down to maybe as low as 3,5 - 4V. I have done a lot of testing of this and found it to be so- on spektrum at least. However, as he is using a switch mode BEC of unknown spec, the minimum voltage required could actually be a fair bit higher than the receiver requires. If the unit does not deploy an LDO chip, and has no pass through circuitry, then the minimum voltage required to maintain the output ( 5.5V ) could be as much as 7V or more.

Trouble is, we really dont know how the BEC chip works as far as drop out and pass through is concerned

Of course, assuming it still works OK, then the OP could run some tests to ascertain this.

[Tim Mackey]

Erfolg - the programming should not affect the BEC - only the LVC.

( and of course the motor performance timing etc )

Edited By Tim Mackey - Administrator on 28/04/2011 11:47:57

[Erfolg]

I have set the programming card "Cut of Voltage" to 3.0v, as I thought this was prudent, and set the "Cut off Power" to reduce.

 

Not being knowledgeable in these things I wondered if the current draw could pull the voltage down so quickly that the voltage went below 3v. That is why I wondered at what voltage the Rx would stop functioning.

 

The Tx is one of those Weston Tango 6, Orange/red types, which I have been considering replacing with another make.

 

I have just got the Weston blurb out which came with the Tango which states amongst other things, "operating voltage 3.5-6.3V"

[Erfolg]

I have just put the battery on charge.

 

it was showing 11.72v at the start

 

the cells were at 3.91v, 3.92v, 3.93v

 

charge rate being 1.5amp.

[Tom Wright 2]

Having read though the all the posts again i think ,it is unlikely that the problem was the battery although it would be useful to know the results of testing the system before re charging the lipo.Just seen your last post Erflog,that confirms  the above and Tims comments,although there is still the question of joints and connectors to consider,and the possibility of radio interference.

 

TW2

Edited By tom wright 2 on 28/04/2011 12:26:17

[Peter Beeney]

I think I would generally agree with Tim. The regulator will generally go on giving an output, on a falling input voltage, right down to virtually zero. I’ve personally never seen one that didn’t. This one appears to be a SBEC, or a switch-mode regulator, I’ve never checked one of these, so I can’t give a definitive answer, but I’d very much suspect that it’s the same.
A 35 MHz rx will function down to 2.8 volts, I discovered that when I was idly experimenting with how rx range is affected by low voltage, a while back now.

It’s fairly difficult to envisage the ESC allowing a three cell pack to get right down to these sort of levels, should not the motor supply cut off point be at around the 9 volt mark? Also I’ve understood that it then needs to be re-set by closing and opening the throttle? To reduce the battery voltage would not the motor still have to still be running, albeit slowly, anyway? There would certainly have to be a fair load applied somewhere.

A reading of 18%, - is that what has been used or what is still left in the pack - is either a voltage reading of around 9.6V or 11.9V, depending on the application. I very much suspect the latter. The fact that the pack recovered to 11.72V, about 60%, after standing for a while might suggest there is little wrong with it.

It does seem as though it might stand a small dose of closer looking at, the fact that the motor appeared to be a bit off-colour to start with might be significant. The clunk, (noise?) sounds intriguing. Sorry!
Is this an indicator of trouble?

Just as a point of interest, my Spektrum AR500 rx continues to operate down to 2.7 volts, 100 millivolts below the 35. At this point the servos are also showing signs of being a bit lethargic, sometimes refusing to start. Below that the rx came to a full stop, too.

PB

[Erfolg]

Is there a consensus arising of what the probable issue might be?

 

As importantly what might be a solution.

 

 

After recharging, I have just run the motor on the ground, there seems to be no obvious issues. The motor run was 30sec, as i did not want to overheat the battery, and 30 secs is generally more than I would run, then hopefully at least 3 minutes before needing to run again, thereafter the motor run being 5 -20 secs. The servos seemed to work as normal, as did the motor.

 

What is indicator trouble?

 

I feel I should be out today, not here.

Edited By Erfolg on 28/04/2011 14:19:02

[Tom Wright 2]

Erfolg.

Unless the battery is in a significant blast of cool air i doubt whether it would cool down much in three mins,it obviously gets pretty hot , is the ESC/BEC is in the same compartment?

It sounds like a higher C rated battery could reduce the probability of thermal problems.

I still think that running the system before re charging ,and measuring the BEC O/P voltage could have eliminated any lingering doubts.

Is it possible that the model entered a hammer head stall ?and the dive was simply caused by that? the model looks a fairly clean design and would soon cover 200ft vertically.You could soon check that out next time you fly ,and it would  eliminate another theory.

 

TW2.

Edited By tom wright 2 on 28/04/2011 16:30:35