RE: RX voltage display

RE: RX voltage display
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RE: RX voltage display - 10/26/2004 6:27:04 AM

sfsjkid

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Joined: 12/12/2003
From: fremont, CA, USA
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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.

< Message edited by sfsjkid -- 10/26/2004 6:31:45 AM >

(in reply to Mike01)

Post #: 26

RE: RX voltage display - 10/26/2004 7:01:49 AM

islandflyer

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Joined: 6/23/2004
From: Kaneohe, HI, USA
Status: offline

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).

(in reply to Mike01)

Post #: 27

RE: RX voltage display - 10/26/2004 4:12:33 PM

BillS

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From: Greensboro, NC, USA
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WilsonFlyer

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

quote:

You'd think with technology progressing with new radios like the 14MZ from Futaba and RX's that can now report back altitude, RPMs and just about anything else

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

quote:

Now... What we NEED is a real-time, two-way amp usage reporting system that's constantly reporting draw back …

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

(in reply to WilsonFlyer)

Post #: 28

RE: RX voltage display - 10/26/2004 4:29:34 PM

Mike01

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From: Brooklyn, NY, USA
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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?

(in reply to BillS)

Post #: 29

RE: RX voltage display - 10/26/2004 4:42:04 PM

Flying Geezer

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Joined: 4/12/2003
From: Bowling Green, KY, USA
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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,

_____________________________

Flying Geezer
Hughes RC

(in reply to BillS)

Post #: 30

RE: RX voltage display - 10/26/2004 5:04:39 PM

BillS

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I’ll pass on the bait.

(in reply to Mike01)

Post #: 31

RE: RX voltage display - 10/26/2004 5:19:55 PM

Mike01

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From: Brooklyn, NY, USA
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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?

(in reply to BillS)

Post #: 32

RE: RX voltage display - 10/26/2004 5:55:27 PM

JNorton

Posts: 3137
Joined: 1/29/2002
From: Montague, MI, USA
Status: offline

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

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Have desk ... Will Fly....
Saito Member #467

(in reply to Mike01)

Post #: 33

RE: RX voltage display - 10/26/2004 6:08:42 PM

BillS

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From: Greensboro, NC, USA
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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.

(in reply to Mike01)

Post #: 34

RE: RX voltage display - 10/26/2004 6:16:27 PM

JNorton

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From: Montague, MI, USA
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Mike01
An article describing a practical battery gage was in the October 4th issue of Electronics Design.
http://www.elecdesign.com/Articles/ArticleID/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

_____________________________

Have desk ... Will Fly....
Saito Member #467

(in reply to BillS)

Post #: 35

RE: RX voltage display - 10/26/2004 6:20:02 PM

Mike01

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From: Brooklyn, NY, USA
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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.

(in reply to BillS)

Post #: 36

RE: RX voltage display - 10/26/2004 6:44:19 PM

BillS

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From: Greensboro, NC, USA
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quote:

using a voltmeter and history a hobbyist can accurately determine a safe operating range

Correct.

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

quote:

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.

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.

(in reply to JNorton)

Post #: 37

RE: RX voltage display - 10/26/2004 7:28:06 PM

sfsjkid

Posts: 576
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From: fremont, CA, USA
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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

< Message edited by sfsjkid -- 10/26/2004 7:41:09 PM >

(in reply to BillS)

Post #: 38

RE: RX voltage display - 10/27/2004 5:23:44 AM

Hangtime

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From: Babylon, NY, USA
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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!!

(in reply to sfsjkid)

Post #: 39

RE: RX voltage display - 10/27/2004 3:51:47 PM