AirmanAirhead

Can I add a small battery to a T-28 to run the receiver? I just lost all power after a flight on my stock Ahm 1800 battery. Lost power and control. That's never happened before. Couldn't pull out of a dive. Lot's of glue later, I'm almost ready to fly again. But I'd rather not go through that exercise again!

If I can (I note that there is a battery slot on the Rx) what do I use?

Thanks,
JN

SkunkyMagoo

Crap man, HOW LONG ARE YOU FLYING FOR?

Just get an external BEC.

eflight-ray

Yes you can add a Rx battery, (4.8v), BUT you must disable the BEC supply coming from the ESC, just diconnect the center red wire from the connector. If you look carefully there is a little plastic retainer that holds the socket in the plastic housing, lift it and pull the socket out, just tape it back.

The next BUT, why do you need to do it? You need to analyse why the power went.

Was it the flight battery draining too low?, the motor should have shut down long before the Rx.
Did the BEC side of the ESC fail?, the 5v regulator has failed?
Did the Tx actually fail and the Rx shut down to safe mode?
Was it interferrence that shut things down?

You really need to know as just putting a Rx battery in may not solve the problem.

AirmanAirhead

E-Flight Ray,

Thanks for the the good questions. Actually, I wonder the same things and just jumped prematurely to the battery question. To date, I never had experienced such a complete power loss. I try not to run things to the brink for that very purpose. I also understand that the ESC or BEC is suppose to allow me at least enough juice to bring it in gliding. I had no ability to do that. Everything was "off". When I put that battery on my Cell Pro 4s charger, it read 6% left. I assumed that I should only be able to drain 80% off before the cut off. This in the past has been my experience.

So what do you suggest? How can I trouble shoot some of the questions you raise?

Thanks
JN

eflight-ray

Have you checked the radio out since the crash?
Check Tx batteries?
Checked for range?
If you still have the near discharged lipo, (not re-charged), use that to power the model.
Check all connections, servo to Rx, ESC to Rx, battery leads and connectors.
Check the Rx crystal is firmly seated.

If by chance you haven't already charged the lipo. (I wouldn't recommend this with a fully charged lipo as heat build up while the model is static and can do more damage).
Connect it to the model and see how long the motor will run for, and when it cuts whether the radio gear still works Ok, lots of servo extremes. I would have expected the servos to run long enough for you to get bored. If you have throttled down after the cutoff and then throttle up, the motor should run for a few seconds before cutting again and the servos still continue working.

If it doesn't, I would suspect the ESC is letting the lipo go too low, as if it thinks there is a 2s, (7.4v) pack connected instead of a 3s (11.1v). But I doubt it unless the ESC needs manual setting for the LVC, (Low Voltage Cutoff), most are auto detect.

As I said this is just a guess. But a total loss of control is most likely to be a radio/connection problem. Trouble is after a crash we usually pick up the bits plug them together and it all works, so we often never know why.

AirmanAirhead

E Flight-Ray,

Thanks for taking the time to be so complete. Yes, you are right, I wanted to get things back together again that I already recharged the battery wanting to to see if it was OK, etc. Next time I fly however, I'm planning on bringing it in before it is too low, then put it on my charger just to check to see what' left. Then I'll do your static test to see if I lose all power to the servos. Since I know there was 6 % left right after the crash, I can duplicate that level fairly easy using my charger as a guide.

In the future I'll also be more aware of timing my flights. It's just darn hard when things are working well! It's seems almost every flight there is something to learn.

Thanks again for your time.

JN

raming

I have flown my new PZ T28 for about 10 flights and am using a 2200mAH 3S battery. Here is what I do to ensure that I don't run out of battery in mid flight:

1. Set Timer on Transmitter for 6 minutes. At 2/3rds throttle this runs down the battery to about 60% which is best for ensuring long battery life.
2. Use an Audible Alarm on the Battery Balance connector while flying and set it to 3.7V/Cell. This ensures that you bring her down if the batteries are severely drained. The best gizmo for this is the Integy C23212 Lipo Voltage Checker/Warning Buzzer and costs about $10. When one or more cells goes below the set point, it produces a loud alarm which can be heard while flying.

fhhuber

Generally a complete loss of control for the T-28 will indicate a bad connection between ESC and RX, sometimes between battery and ESC.

The ESC should kill power to the prop LONG before you have inadequate power in the battery for the RX.

If you are thermalling long after the low voltage cutoff you are asking for trouble. Even putting in a separate RX pack isn't going to help you because you can still thermal well past the time that you will have RX power.

The LiPo alarm is the answer. Don't bother with a separate RX pack.

JetPlaneFlyer

Or it could be the famous 'Brown Out'. This is caused when the BEC in the ESC fails to maintain adequate voltage supply to the receiver, usually caused by a cheap ESC with inadequate 'linear' type BEC.

kyleservicetech

Yeah, I've seen this happen more than once in our club.

BEC Linear Current Rating
http://www.wattflyer.com/forums/showthread.php?t=63779

solentlife

You say that the LiPO showed 6% after flight - that I take it was some time after the plane came down ? So that would be RESTED battery !

That indicates then that you literally hit near ZERO on the battery in flight and your crash is a matter of flying TOO low on battery such that all power was lost to ALL ...
I'm surprised if the LiPo will survive that in good condition ...

80% is NOT a cut-off ... that is the level that you can use safely ... a Low Voltage cut-off usually carries on past 80% use well into potentially damaging low voltage of pack ...

Question :
a) How long were you flying ?
b) Did you have warning by motor slowing down or cutting out ?
c) How long have you usually flown this before WITHOUT failure ?
d) Did motor slow / stop and you gave it another full throttle stab and it started up again ?

Nigel

pizzano

Personally, I see no real need or advantage to adding a seperate "battery balance connector" or an additional battery "audible alarm" to a plane like the PZ T-28.
The vast majority of pilots I'm around who fly this bird (even modified with 4s 2600mah power systems) rarely fly longer than 12min. and seldom spend time "thermal" chasing........not to say that this plane dosen't have good a glide rate or is not capable of "floating around" at sustained altitude, rather it's more of a sport acro bird better suited towards fast and quick manuvers, which generally translates to shorter battery flight time.
Setting the flight timer on one's TX (if available) is the more common practice for any flying with any model (regardless of type of ESC/BEC being used), especially once one has experience with the models flight charcteristics and power consumption.......an audible tone setting giving ample amount of "fail safe" cushion is wise as well.

For me, adding more power consuming equipment requiring additional "attention to detail and monitoring" does not seem to make sense on a plane basically stock designed for moderate sport flying (power speed mod's exempt).......I have enough to think about just keeping the plane flight worthy and airborne......

JetPlaneFlyer

No, 6% remaining would be a voltage of roughly 3.5V per cell minimum. Even under load that would be at least 3v per cell, so total battery voltage about 9-10V.. That's more than enough to keep the radio powered.

Unless you are gliding around in thermals it's impossible to run a (2s or higher) LiPo down far enough to lose power to the radio. The LVC kills the motor and the plane comes down long before you get there.

pizzano

"Unless you are gliding around in thermals it's impossible to run a (2s or higher) LiPo down far enough to lose power to the radio. The LVC kills the motor and the plane comes down long before you get there."

+1.....unless someone didn't bother to charge their TX before hand and was asleep at the sticks..

solentlife

LVC occurs ... you can then shut throttle and re-open it to get a short run of power that really is last bit of battery pack if he has low LVC set - you should know that ...

We don't know his power draw ... and if he hit LVC ... and then shut / opened throttle again - he would drag out the last bit that is AFTER LVC ... he may not have realised it and not be on a final circuit as you or I would do as soon as that happens. He may have tried to continue flying ...

I have had a model do this when I tried to use that last few sec's power after LVC happened ... I had the 20 secs or so power - then EVERYTHING died ... seriously..... I reckon I still had servos ... but the model was doing own thing and appeared to be dead as the proverbial Dodo...

That's my point and why I asked the questions at end of my previous post ... to see if that did happen.

Nigel

JetPlaneFlyer

Indeed i do 'know that' but LVC still only takes the battery down to the LVC voltage (3.2v or whatever LVC is set at). LVC by definition cuts power when the battery reaches the cut-off voltage.

Even if you do lots of re starts it wont go below LVC value. The re-starts are simply due to the voltage bouncing back when not under load, LVC cuts in again as soon as the voltage once again drops to the threshold value. If you keep doing re-starts then soon the battery no longer 'bounces back' above the LVC value the motor will no longer re-start. By that point you are on the ground anyway.

It's impossible to run a battery below the LVC voltage using the motor, it just cant be done. I have several times inadvertently hit LVC and used re-starts to get back to the landing strip, right to the point that the prop simply would not turn any-more. Never have i lost radio control in those circumstances.

solentlife

Sorry but not true in all ESC.

In some and as in the 'yellow cased' unbranded I had (probably a Mystery) - the LVC cut as we know ... but idle then fullstick then allows you battery power not as a result of bounce back - but real access to battery.
You fly and motor slows and stops - but power is still being dragged down by motor even though stopped. The voltage dips seriously because now there is so little left in the pack - it cannot hold it up...

I actually bench tested to see if that was true on this one ... and that's what I reproduced. I used the pack that was in the crash - not wanting to risk another. I no longer buy those from the ebay seller ... But I do not believe they are the only ones.

TBH - your description is first time I hear that explanation of 'emergency power after LVC' ... not saying I don't believe you - it makes sense sort of ...

But I have never seen an ESC do more than 1 restart after LVC ...

But as I describe does happen. I have the model with the scars and the ESC tested on bench.

Nigel

kyleservicetech

That's one good reason to never fly more than perhaps 70-80% of the battery on any given flight. First, it's likely pretty hard on the battery. Second, if you've got to do a go-around for whatever reason, there is still some juice to do it, without the motor shutting down over the trees, corn field, deep stuff, what ever.

This is easy to manage, simply use a timer for your flights.

As for the Castle Creations ESC's and likely many other brands, you can program the ESC to either shut the motor off on Low Voltage Cutoff, or reduce power to the motor to prevent the battery from going below the LVC that you've programmed in. All of my CC ESC's are programmed to reduce motor power at the LVC on the battery.

JetPlaneFlyer

Nigel,

Al,l i can say is I've never experienced what you describe. I use several Mystery brand ESC's (the blue heatsink type with switching BEC) and they certainly don't do it, if they did I'd have experienced it. Possibly some cheap off brand ESC's do bypass the LVC if you re-start, it would be best to avoid them if that was the case.

In any case it is really a moot point because the OP didnt do a re-start, and he apparently had about 10v left in his battery (6% or 108mAh remaining), which is low but still more than enough to power the receiver for the brief time that the T-28 glided down to earth with a dead motor. It would be a different proposition if it was a sailplane that could fly for several minutes (or more) after the motor quit.

solentlife

I don't disagree ... but unfortunately the world doesn't always do what we want !!



Nigel

fhhuber

I have experienced the LVC "creep down" in response to plugging in a partially charged pack.

Auto-detect of pack voltage and the corresponding auto-set of LVC in some cases does not "count the cells". Some ESCs set the LVC to a percentage of initial detected. With these ESCs plugging in a partially charged pack can result in LVC being below 2.5v/cell for your LiPo pack.

Some of the ESCs affected by this CAN NOT be set for LVC except "high" or "low" with "High" aiming for 3.5v/cell (if its LiPo and plugged in at 4.2v/cell) and "low" aiming for 3.0 or 3.2 v/cell.

VERY CAREFULLY read your ESC's instructions about how it determines where to set LVC.

If your ESC sets the LVC by a percentage of initially detected, then you MUST use a meter to test and ensure the pack is FULL when you power up the ESC.

JetPlaneFlyer

That's a good point!

solentlife

I thought that is only when they detect NiXX packs ... that LiPo was as set
....

Here's a cut and paste from Hobby Wings ESC :

I just assumed that was usual for all packs ?

Nigel

fhhuber

I've got a Jeti ESC that is auto-detect only .. always sets the LVC by a percentage of initial pack voltage. Supposed to be LiPo appropriate and its fine if the pack is full when detected.

solentlife

mmmm just had a Google on Jeti ... and says what you said except it does say it auto-detects TYPE and number of cells ...

That's same as most other ESC's .. except that other ESC's allow setting of the voltage / % LVC.

Trying not to be difficult - but does the ESC not detect it's a LiPo and set up as others do ? Automatically changing from % to set volts ? even if you cannot alter the setting ?

I have to ay that if it doesn''t set a specific voltage to LiPo - then it's surely a bit iffy ?

Nigel