sfsjkid

I think both points of view in this thread are correct. Most, if not all manufacturer of nicads will tell you that voltage is not a good indication of charge in the battery, yet using an ESV gives me an indication of the state of charge.

No, I cannot tell the state of charge if told the pack is at 5.060 volts. However, knowing that I charged my, say, T-34 the night before, starting the begining of the day at 5.440 volts, hitting 5.060 volts after about 4, 10 minute flights, I know I am still safe to fly for about 6 more flights, with this particular plane. Putting my this plane on the discharger and noting the time remaining, comfirms what my voltage readings, and my judgement is telling me. So what I'm trying to say is, while I am measuring voltage, which in itself is meaningless, given everything I know about a particular plane, and how I prepared it, what I'm actually doing is getting a sense for the actual current remaining.

I don't know about other clubs, but ours requires a voltage check before each flight. I've noted that people have different methods of coping with the go, no-go decision, some charge immediately after going below 5V, others charge before each flight etc.. Seems to work given the fact that there are few planes lost to bad batteries.

islandflyer

I guess I solved my RX battery doubts by going way overboard: 2200 Mah on my 1.20 or smaller planes, 4400 Mah on my 33% SA plane, and two 4400 Mah on my 42% SA plane (all LiIon). And I still measure Volts under 1 amp load on landing, and before take off (even if it only makes me sleep better, it works fine for me).
It seems that wether the users are knowledgeable or plain consciencious makes little difference: these rarely have any problem.
I am more concerned about the (fairly or really) new guys who usually were sold equipment with grossly over-simplified instructions (via LHS or on line); they also usually don't want to spend the extra-money to buy a decent chager/cycler, a decent tester, or larger than stock batteries. In many cases, when you start telling them about safety and reliability, they don't want to hear it (like you're ruining their "innocent harmless"fun).
Eventhough we have a club, we fly on public property and therefore cannot enforce club safety rules (or any rule, for that matter).

BillS

WilsonFlyer

Voltage reporting is the first step and the easiest variable for everyone to understand, especially the manufacturers.

Where might information be found about the ‘report back’ features?

Likely you are aware that it would not be too difficult to write code to calculate time remaining on a battery pack by picking up voltage in 30 second intervals under flight load conditions. Some automobile computers calculate the number of miles to empty. The problems with varying rates of usage are similar. Batteries have the additional complexity of a nonlinear discharge curve and a knee, which must be avoided. For purposes of writing experimental code battery discharge is sufficiently linear over most of the usable range. It is suspected that you could build a spreadsheet to calculate the remaining battery time in less than half a day.

But first the manufacturer must be convinced of the need for voltage downlink. The conversation here is less than convincing. There are far too many willing to accept status quo.

Bill

Mike01

So no one wants to try to tell me what the remaining capacity of my RX pack is?

I thought voltage and voltage under load was what you guys rely on to safely fly your planes? Surely you can at least come close to telling me what the remaining capacity is based on the numbers...resting voltage and votlage under load...that I provided?

Resting votlage: 5060v

Voltage under momentary 1amp load: 4.724

Going once?

Flying Geezer

My Feedback: (14)

Let's get serious AND scientific. You can determine the approximate flying time left in your battery pack by reading the voltage, knowing what size battery pack you have, and the average current draw of your airborne system.

THE BIG SECRET is reading the voltage loaded. You can use gin, vodka, 2 six-packs, and many other sources to get loaded. I personally prefer Kentucky Bourbon. When you are sufficiently loaded, approach the aircraft very carefully, you wouldn't want to fall on a wing or step on a stab.
connect a voltmeter to the battery, receiver, charge jack, etc, so that you have a straight connection to the battery. You will then be able to look down through the monokote, foam wrap, shrink wrap, the metal cannisters, directly into the battery. When I do a loaded voltage test I can always do this. The current in the battery is red with streaks of yellow in it. I always mount mine vertically, so it's easier to see how much is left, or how much is gone. Are the cells half full or half empty? There is a difference you know.

If on this inspection, you determine that you have enough current to fly one more flight, and there aren't too many yellow streaks in the current, you may fly after a 2 hour wait and half a pot of black coffee.

Hope this helps,

BillS

I’ll pass on the bait.

Mike01

Why?

I'm not going to lie...the pack is what it is.

If you claim voltage is a useful way to measure capacity, why won't you try and tell me the capacity of my RX pack?

JNorton

My Feedback: (2)

Mike01
If you go to the manufactures web page and download the discharge curves for that particular battery you can get a pretty good idea.

Myself when the individual cell voltage reaches 1.1 volt per cell or 4.4 volts I quit flying. Because I like to use a voltwatch on my receiver I can also move the servos to their extremes and see what the peaks / valleys are on the display. It might not meet your requirements but I know I can fly 5 - 15 minute flights and then I recharge the pack.

It's a no brainer.

John

BillS

Now, now Mike.

1. The question is sucker loaded.
2. Voltage is not irrelevant.
3. The problem is not technical.
4. The problem is a people problem.
5. You missed the point.

Pass.

JNorton

My Feedback: (2)

Mike01
An article describing a practical battery gage was in the October 4th issue of Electronics Design.
http://www.elecdesign.com/Articles/A...8764/8764.html

My only point is using a voltmeter and history a hobbyist can accurately determine a safe operating range.
Not an exact battery remaining charge level but a range for safe operation.

Presently I don't see it happening that you'll see the receiver battery voltage on the transmitter because that would require an addition RF frequency to relay the information.

John

Mike01

The question is not loaded. The pack has what charge it has. I read the voltage, and I read voltage under load.

Since you are not going to bite, I will tell you the capacity of that pack. It was discharged to 0.9 volts per cell and then stored for three months. It had no useable capacity left, yet still read over 5 volts and 4.7 under load.

Get what you want from that...it's not my planes that are crashing at your flying clubs due to battery condition.

BillS

Correct.

If battery safety became an issue I believe in the next five to eight years we could see a solution.

Maybe but it depends upon the approach to the solution.

In any event no solutions will come about until we become interested and ask the radio manufacturers for a solution.

sfsjkid

Bill, if you been reading my comments, I think it may be overkill, but here is are systems available today which can do what you want, and it downlinks a bunch of other parameters as well. I think it needs a HUD but it is a start.

Check out,

http://www.eagletreesystems.com/Seagull/seagull.html
http://www.sky-spy.bigstep.com/generic.html?pid=0

Hangtime

My Feedback: (19)

An outstanding thread; great discussion. All the prime 'nails' were solidly whacked.. and the key point remains; ain't no such thing as a 'reliable gas gauge' for a pack. Cripes, change just the temperature of the system by 15% and whatever info you thought you were getting from the 'gauge' previously is rendered suspect .

For a large portion of the modeling public, the mystical magical world of on-board battery management is surrounded by myth, wives tales and to make it worse theres the on-going deliberate misinformation propogated by charger manufacturers and battery salesmen. The greatest value in this discussion has been in dispelling some of that, if not between the respondents here then hopefully for those that read this stuff and mull it over without getting 'into' the debate... this thread should be preserved, one of the best I've seen in years.

For virtually all of the posters in this thread, reality, homework and practical experience have lead you to decision points that work effectively for you and keep you outta trouble... multiple paths to the same basic conculsions:

1. An on board battery gas gauge is problematic because of the nature of the often wild vargaries of the applications.. what works effectively on a low impedance nicad won't provide the same answer on a higher impedeance NiMH .. and what worked yesterday on either of 'em may not offer up the same results when the temperature changes by 20 degrees next week. What works for Joe ain't necessarily the right cuppa tea for Jake.

2. Knowing what the nominal capacity, age and condition of your pack(s) is, what the state of charge is when you start and what the average draw of your system is coupled with common sense and observation and a good trusted loaded ESV is your best 'defense' against a dangerous or tragic loss of an aircraft that may not have been saved by any other means than simply applying a 10 second .5 to 1 amp load before taking it outta the pitts.

3. Redundant/parallel systems and dual switches greatly improve reliability. Appropriate initial battery type/technology choices are a big key to success; handicapping a power system choice to save weight sometimes ain't the best way to obtain better flight performance.

4. The nature of the hobby attracts all types.. those that want to 'buy' the knowledge and those that understand that the 'homework' is the key point.. the raw data garnered by any device is useless without an experienced mind to interpet it.

Telemetry solutions are part of the landscape these days... as pointed out above. I've had some small opportunity to play with some on-board systems and the wealth of info is absolutely priceless in some circumstances and in particular it's a very valueable tool for trouble shooting and improving the genre. Good stuff already available and even better stuff is in the pipeline... and all of it useless data with out an 'experienced' mind to interpet it.

Sad to say that even with low voltage warning alerts, flashing lights and wailing 'barkin bettys' howing in the pilots ears, planes are still gonna go in. I'd hate to tell you how many boats my kid has pulled off the sandbar in our bay; all of 'em were equipped with expensive and fully functional depth finders, GPS and there's big flashing physical 'aids to navigation' all around the sandbar.. How many of us have seen pilots pull the ESV out after the crash instead of before that flight? And then griped about not having 'some way' of having 'something' do their thinking for them so they don't have to exercise the grey matter to make a decison?

Again.. great thread gents, enjoyed it immensely!!

BillS

Everyone who reads here:
1. Agrees that voltage is not the absolute indicator of battery goodness.
2. Have few if any battery related crashes.
3. Probably read the RX voltage frequently.
4. Probably owns several voltmeters.
5. Goes to a remarkable amount of trouble to read the
RX voltage.
6. Occasionally forgets to check voltage.
7. Probably would not fly if voltage were in a 4.5 to 4.7 range (NiCad).
8. Believe that safety is important.
9. Believe crashes represent a safety hazard.

Every flight field has a few who we shall call ‘Battery Reckless’. Every flight field has a group who we shall name ‘No Battery Knowledge’. ‘Battery Reckless and ‘No Battery Knowledge’ create almost all of the battery related crashes. The crashes are no less dangerous because someone who might disserve to lose an airplane caused them.

An easier and more convenient method to know the battery voltage at all times would help everyone. Also it would make the flight field safer. I think the inconvenience associated with checking batteries deters everyone from checking as often as they should. The radio manufacturers can easily remedy the problem with technology and at small cost.

Safety is the subject. In five to eight years the technology would filter down to everyone. Wouldn’t it be great to go to the flight line and glance at ‘Battery Reckless’transmitter and know that he is probably flying battery safe. Or better yet demand that he land because he is definitely battery dangerous.

Granddaddy didn’t want a fuel gage on his car. He stuck the tank occasionally and mentally calculated when fuel would be low. Granddaddy didn’t want an oil gage on his car. He changed the oil. He checked the oil. He knew the car burnt a little oil. He also didn’t let Grandma drive.

JNorton

My Feedback: (2)

Bill S.
I agree with everything you wrote.

However I'm really quite curious. Did anyone take the time to go to the post I mentioned previously? That gage "system" or something like it would work. You would need to be able to calibrate it to the chemistry and MAh rating of the pack. It could then determine the average current useage after a couple of calibration flights and then give an accurate assement of the batteries charge state. Heck you could do it with a PIC and a USB port connection. A real battery gage shouldn't be that far out in time.

Now all we have to do is look at it!

John

JNorton

My Feedback: (2)

Opps meant to list the address for the article again.

A practical battery gage was in the October 4th issue of Electronics Design.
http://www.elecdesign.com/Articles/A...8764/8764.html

Hangtime

My Feedback: (19)

ROFL!! He also hated cars with 'idiot lights' instead of guages.

Good post, Bill!

I did.. and I agree.. just a matter of time. At less than 5 bucks for the chipset and with a decent IC to integrate it, it would be a very welcome device for all of us.. 'battery challenged' or not. Of course, I may elect to continue to probe the pack with a loaded ESV and make my choices based on that and reinforced by the 'gas gauge'... but that's just because I'm a 'gramps' when it comes to stuff like my planes and grandma.

BillS

John I read the link and was impressed. There has never been any doubt in my mind that the calculations of remaining battery can be extremely accurate.

However for the purpose of simplicity and to avoid confusing the issue with technical details for many to argue and fret about it was not mentioned. It is clear that if the baby steps are not taken there will not be an Olympic runner.

It appears that many are stumbling over:
1. It can’t be done syndrome.
2. It cost too much.
3. It’s not a perfect indicator.
4. Status quo is OK.

Voltage as a first step is not perfect but it is a reasonable starting point. Voltage is used now. Voltage should be easy for everyone to understand. Most everyone except ‘Battery Reckless’ and ‘No Battery Knowledge’ use voltage as a go/no-go gage currently.

It is necessary for a sufficiently large number of people to believe safety is important (people and airplane) and that better techniques are available and also to convince the radio manufacturers. Otherwise safety features will not be added to the radios.

Lets lean on the radio manufacturers for better and safer features.

There might be several techniques that could be used to avoid using a model frequency.

BillS

Hangtime,

Glad this thread lightened up a little. Maybe there is hope.

Yes Granddaddy really despised idiot lights. But by that time Grandma insisted on driving.

The necessity of redundancy is understood. Granddaddy continued to stick the tank for years after the gas gage. When the necessity for frequency control (pin box) goes away there will be many old timers and good friends who will not fly without a pin. Things change and it takes time to adjust.

Has it occurred that maybe in flight loading and voltage testing might be a more accurate indicator than a fixed load condition? Most including me use a fixed load for everything from 40 size airplanes to 35lb airplanes. The current draw and voltage cannot possibly be similar. The wind load across control surfaces cannot possibly be the same on different forty size airplanes. A servo bind will play havoc with battery discharge.

Bill

Hangtime

My Feedback: (19)

Hiya Bill! There's always hope!!! It's why we build new planes to replace the ones we just 're-kitted'.

One of the neatest things to come our way recently has been telemetry and in particular the 'logging' capability of most of these systems to review flight data. One thing that rocked me back a bit was whats happening to voltage on board relative to actual in flight servo loads. Have a gander at the telemetry review I wrote some time back on the RCATS setup..

[link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=317]RCATS Review[/link]

Based on what I've seen, a lot of my presupposed guestimates were tossed out.. baby and bathwater. Here's a data strip garnered in an 1/3 scale Extra with digital servos doing a pattern aerobatic routine..



The same bird on a 4 cell pack had negative voltage spikes uncomfortably close to tolerable Rx minimums, and in fact it tripped the PCM lockouts more than once. In this setup, flown with a 5 cell sub-c pack he was ok... just. A later upgrade to a parallel 'A' cell 6v pack system showed a comfortable decrease in low voltage max spikes, he's happy and I got an education.

The high cost of 'live' downlink at this time is somewhat prohibitive, but the cost of a 'logger' for playback is less than a 100 bucks now, and even those prices are comming down... and seeing what's going on on-board even after the fact has immense value in helping make decisons about whats 'good', what's 'marginal' and what's not suitable; period.

Good things are in the pipeline.. and just like gramps, I'll be 'grudingly' integrating the stuff into my own flying decisions that decreases the risks and improves the reliability.

Cheers to all of yah!!

sfsjkid

Correct Bill, the systems mentioned earlier uses 900MHz with spread spectrum (Seagull), 2.434GHz HAM band (Sky-spy) and the RCCATS system available with both.

BillS

sfsjkid

Thanks the web sites were very interesting. Incidentally it has been over ten years since my last battery related crash.

General field SAFETY

The somewhat hidden agenda in my comments is general field safety over the next ten years. Unfortunately one individual can only improve field safety by about 1%. General solutions might improve safety by 80%.

All flight fields seem to have a few who are reckless with batteries. Fields also seem to have another large group who simply don’t understand battery technology. There is yet another group who are sometimes good builders and good flyers who are convinced that anything electrical is too complicated to learn. All three groups are not going to spend money on solutions when the problem is not recognized.

If the radio manufactures were to believe battery voltage represented greater safety maybe in ten years 80% of the transmitters in use would display RX voltage. Those who don’t understand and the too complicated group would quickly and unknowingly become knowledgeable by glancing at the transmitter RX voltage. It wouldn’t take long to gain an understanding of the significance of decreasing receiver voltage. Cause and effect could be closely correlated.

Everyone including the safety officer could closely monitor those who are reckless. At our field there are a couple of reckless types that could be monitored by walking to the flight line and glancing at the in flight voltage. If the reading were near the knee on the battery curve we could request they stop flying. If they didn’t stop flying they could be given their walking papers for safety violations. With the current system there is simply no way of knowing when the reckless are getting into trouble.

backfire

I agree. It's as old as NiCds themselves, the remaining charge in a NiCd battery (or cell) can not be determined accurately without history (battery design capacity, initial charge state, and the integration of the time/current discharge) due to the relatively flat discharge curve. However, I still do find the 'VoltWatch' useful. For a given setup, one becomes familiar with the gradual retreat of one or two indicators each time it is turned on, and also the depth of indicator retreat as the servos are exercised (an indication of increasing battery ESR). Accurate? No, but better than nothing. And, while not a substitute for flightline vigilance, it might catch a low battery condition caused by a system accidentally left on. I have seen it catch a bad switch.

BillS

Hangtime,

The post probably indicates that I am also battery challenged. It will take a while to dissect the information.

In the meantime a few questions.

Sub-c and parallel A should have represented approximately the same capacity. Sub-c (1500 to 1800 ma) and A’s at 800/900ma each. Was the parallel application important or was the pack size different? The sampling must have been every 12 seconds. Do you know how the data compared to conventional voltage under load testing before and after the flight? How much battery rebound was seen when checked before the next flight? It appears that there was about a .4v loss in three minutes of flight time. What was the loss for the entire flight?

More questions later.

Bill