By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by CML

WOT4 Becomes Racing Car

A bit of a head scratcher.

All Topics | Latest Posts

Search for:  in Thread Title in  
Devcon109/02/2018 21:57:28
avatar
1243 forum posts
368 photos

A couple of points, one already touched on..

I once had a connector pin pull out of the servo lead socket/housing, the servo locked out in flight but then began working again on the ground. It wasn't immediately obvious until very close inspection showed the culprit.

I've certainly experienced this in the winter with cold hands, at the point my hands become cold my brain has been sending the correct signals to my thumbs to pull on the elevator and I think that's what they are doing but my eyes tell me a different story with the model reacting as though very little input has been made, I then have to very consciously pull more stick to get the desired input.

In simple terms could your fingers or thumbs have failed to physically move the stick as much as your brain was telling you it had.

Ive always landed when this happens as it's quite an unnerving feeling.

David Gilder09/02/2018 22:16:30
avatar
1839 forum posts
636 photos

Probably a long shot but I have experienced this when flying gliders.....

Downdraft like a Microburst.

This wouldn't need to be excessively strong for a model aircraft but would prevent it lifting!

question

kc10/02/2018 08:16:00
5511 forum posts
161 photos

Everthing has been covered so far ...except the elevator horn being loose in the balsa or the elev joiner being loose in the balsa meaning only half the area moves.  Or a clevis slipping on the thread.

 

Edited By kc on 10/02/2018 08:17:25

ChrisB10/02/2018 08:42:30
1212 forum posts
34 photos

Loose servo or tray, flexing snake or pushrod, ill fitting servo horn,Tx settings, hinges?

Cuban810/02/2018 10:14:28
2031 forum posts
3 photos

I blame Brexit.................sorry joke!

Geoff Sleath10/02/2018 11:36:13
avatar
2720 forum posts
199 photos

Probably witchcraft. Did you notice any flying brooms in the vicinity?

Geoff

Devcon110/02/2018 13:11:07
avatar
1243 forum posts
368 photos

How about a prize or certificate for whoever identifies the cause 😂

Trevor10/02/2018 15:24:07
avatar
290 forum posts
40 photos

Might be worth re-calibrating the ESC, just in case full throttle isn’t. If you see what I mean.

Trevor

Biggles' Elder Brother - Moderator06/03/2018 15:12:42
avatar
Moderator
15429 forum posts
1409 photos

I think I may have found the answer!!

The WOT4 has flown a few times since the incident - no problem - and its scheduled to come to the field with me tomorrow. So this morning I'm pottering around the shed checking stuff out for tomorrow and I gather the batteries for the WOT4 together to check them and if needed charge them. I realise that actually I'm a battery short, I sould really have 4, there are only 3 and have been for a while. I remember that the battery that was in the model on the day of its racing car behaviour I left at the back of the workbench. OK no probs.

So, I check the batteries and I come to the one in question. Probably doesn't really need charging, it only did a taxi out and a 80 yard run down the strip! But I put it on the battery checker,....98% - as I thought. Hang on! 13.6v? That's very low for a fully charged 4s - should be more like 16v+. So I check the cell voltages - two at 4.16V (fine), two at 3.0V! What! Looks like two cells have gone down on the battery.

Just out of interest I put it in the model with the wattmeter attached - full throttle 82W - no wonder I couldn't take off the model weighs nearly 5 pounds!

Its possible of course that the cells "went west" after the incident - but I doubt it. I think I have found the cause of the behaviour. That batterry would have just enough umph to give me a brisk taxi and apparently reasonable initial acceleration. But within a few seconds the power would drop off, add in the fact that as the speed went up the drag resistance would increase and you can see tha,t while initially all may look OK, in reality it is far from being OK!

So what can we learn from this? When I was working with the UAVs we logged every battery into and out of the drone recording individual cell voltages. I'm not so diligent as a retired hobby flyer! But it does show that just taking a few seconds to flip through the cell voltages at the end of charging, even if you don't record them, is a very good idea!

Well, that feels good. I accept those incidents where I get it wrong and stuff it in - we all do it! I accept it when fate decrees something fails despite reasonable checks and maintenance. We learn from such things. What do you learn when it all works? Nothing, except that you were right! Experience is in reality nothing more than the accumulated knowledge of many failures! So I hate it when it goes wrong and I don't know why!

Thanks to everyone who helped, suggested and encouraged. I offer this experienece to you, that you may gain from my pain!

BEB

J D 806/03/2018 15:47:14
avatar
875 forum posts
54 photos

Thats good BEB,you can stop wandering now as to what happened. yes

I check individual cell voltages after a flight. Have found that that this is more likely to reveal a battery on the way out thanan after charge check.

Geoff Sleath06/03/2018 15:54:08
avatar
2720 forum posts
199 photos

I think I had a similar problem on my Riot now I come to think of it a year or so ago. I checked the charge on the 3S2200 LiPo before I fitted it and it showed fully charged (ie 95%+ I suppose) but it seemed very sluggish on my attempted take-off. When I re-checked the battery it was still showing fully charged but a fully charged 2S rather than a 3S.

I just forgot about it until your post reminded me, BEB. You live and learn

Geoff

The Wright Stuff06/03/2018 16:10:19
avatar
1264 forum posts
225 photos
Posted by Biggles' Elder Brother - Moderator on 06/03/2018 15:12:42:

But I put it on the battery checker,....98% - as I thought. Hang on! 13.6v? That's very low for a fully charged 4s - should be more like 16v+. So I check the cell voltages - two at 4.16V (fine), two at 3.0V! What! Looks like two cells have gone down on the battery.

Which battery checker was it, BEB? Measured using the balance lead?

I'm a little confused as to how it could read 98% if it 'knew' there were 4 cells and not 3?

Chris Walby06/03/2018 16:28:19
avatar
540 forum posts
96 photos

The feature (not a problem as its outside the design of the ESC) is that the resting voltage when the ESC is powered up thinks its a 4S, but as the voltage collapses under load so the ESC backs off thinking the lipo is discharge. It all becomes self limiting (been there had that, but mine had just taken off!).

The twist is that if you stick the lipo on a resistive load you can get full current all be it at a reduced voltage the alternative is the cell goes open circuit. The difference will be the RX will loose power and you won't have any control (but then as the voltage recovers the failsafe activates) so it just dead sticks in.

There is no real way of testing lipos without a big (as in high power) resistor and logging individual cell voltages and even then there is a view that stressing lipos does them not long term good!

Ron Gray06/03/2018 16:40:38
924 forum posts
231 photos

But isn't the correct time to check a battery's state just before you fly, both by % but also cell by cell?

Andy4806/03/2018 16:49:11
1333 forum posts
1 photos
Posted by Biggles' Elder Brother - Moderator on 06/03/2018 15:12:42:

So what can we learn from this? When I was working with the UAVs we logged every battery into and out of the drone recording individual cell voltages. I'm not so diligent as a retired hobby flyer! But it does show that just taking a few seconds to flip through the cell voltages at the end of charging, even if you don't record them, is a very good idea!

The answer is to plug in the lipo voltage sensor to each model when you fly it, and set up a warning in OpenTX when the lowest cell drops below 3.4v (and critical battery level set at 3.2v). That way you would have instantly got a low battery warning when you opened the throttle. You were perhaps very lucky that the 2 failed cells were as bad as they were. Had they had a little more charge in them, you might have been able to take off then lost power whilst still low down.

I have every model with a SPort lead permanently plugged into its receiver, and then swap voltage and current sensors from model to model as I fly them.

Andy4806/03/2018 16:52:00
1333 forum posts
1 photos
Posted by Chris Walby on 06/03/2018 16:28:19:

There is no real way of testing lipos without a big (as in high power) resistor and logging individual cell voltages and even then there is a view that stressing lipos does them not long term good!

Yes there is. BEB uses a Taranis, and the current and voltage sensors available for OpenTX will give you precisely these readings.

Biggles' Elder Brother - Moderator06/03/2018 17:28:43
avatar
Moderator
15429 forum posts
1409 photos

OK to try to answer TWS's question - ie how can the checker show 98% with two duff cells - here's how:

First, here's te battery, a 4000mAh 4s Zippy;

battery.jpg


Next up, here's the checker I used - a pretty standard item I think:

checker.jpg

Finally, here's the battery's balance lead connected to the checker:

reading.jpg

Note, 5 wires on the balance lead - as you would expect of course - and the checker tells us the battery is now 95% charged with a voltage of 12.43v. It also tells us (in very small letters at the top centre) that the battery is a 3s!! So, despite a 4s being connected, the checker says 3s - and of course 12.43v is a healthy charged voltage for a 3s - so its 95%.

OK, I should of course have seen the "3s", and the 12.43v should have rang alarm bells (as it did this morning). But I'll be honest - sometimes, you're on auto, you plug the battery in, it says 95%, you think good-oh, and off you jolly well go. I shall be less trusting in future! This is feature of battery checkers we need to be aware of.

BEB

Biggles' Elder Brother - Moderator06/03/2018 17:41:30
avatar
Moderator
15429 forum posts
1409 photos

Andy, yes of course I could use a voltage sensor etc. with my Taranis and I do in my more complex models. But this is winter hack. I fly it on grey cold days and really I just want it as simple as possible.

I have more than enough complex models. Sometimes you just want to plug in and fly! I think I just need to remember to battery check cell voltages pre-flight - not just the percentage charged - to protect myself. It's true that might not give me a very accurate reading, but it will be good enough to spot any major problems - and that's all I need to know.

One or two of you might have noticedI that have a tendancy to over-engineer and over think solutions most of the time! Noooo, surely not, perish the thought I hear you say! But just now and then I can manage technologically minimalist as well! smile

BEB

Devcon106/03/2018 17:55:04
avatar
1243 forum posts
368 photos

Its good to know the cause in the end.

I have a FrSky LiPo sensor installed in all my models, for the relative low cost and only requiring a second connection to be made whilst installing the battery it works for me. I notice FrSky have released a new micro LiPo sensor which means it will tuck away very neatly.

What was interesting BEB was looking back at your description of the event didn't make low power an obvious culprit but hard evidence proved otherwise.

Just shows we need to keep an open mind when fault finding..

(Like the time I convinced myself a new FPV install which lacked picture on my goggles was down to to a failed Video Transmitter when, after swapping in another one I realised I'd not taken the lens cap off the camera... Doohhh)

Biggles' Elder Brother - Moderator06/03/2018 18:01:59
avatar
Moderator
15429 forum posts
1409 photos

No Devcon, good point. We can often form false impressions in the heat of the moment. The model felt OK on the ground - taxi and initail acceleration seems nomal - but obviously died off dramatically, by which time I suppose my attentions were er,.. "elsewhere" as in "Why won't thisdamn thing rotate???!!!"

BEB

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of RCM&E? Use our magazine locator link to find your nearest stockist!

Find RCM&E! 

Support Our Partners
Gliders Distribution
CML
Expo Tools 14 July
Wings & Wheels 2018
Airtek Hobbies
Slec
electricwingman 2017
Overlander
Motion RC
Advertise With Us
Sarik
Latest "For Sale" Ads
What is the main brand of transmitter you use? (2018)
Q: What is the main brand of transmitter you use?

 FrSky
 Futaba
 Graupner
 HiTec
 Jeti
 JR
 Multiplex
 Spektrum
 Other

Latest Reviews
Digital Back Issues

RCM&E Digital Back Issues

Contact us

Contact us