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Old Jul 06, 2007, 01:01 PM
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dick hanson's Avatar
slc ut
Joined Nov 2003
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Good show !
I see sales by all 2.4 mfgrs as good for the modelers .
1- credibility for 2.4 increases -especially for the timid souls
and
2- the many uses and misuses of the technology gets a quick sorting out .
It couldn't be better -
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Old Jul 06, 2007, 01:03 PM
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pda4you's Avatar
USA, TX, Trophy Club
Joined May 2002
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Quote:
Originally Posted by JimDrew
I love getting steamrolled then. Just based on our distributor sales alone, we will ship more than 30,000 complete systems before Christmas. That does not include additional receivers or anything sold to the general public (thousands of which have already been sold that route). 50,000+ full systems by the end of the year is expected.
Impressive for sure Jim - but don't you think Spektrum with the JR distribution channel behind them has sold more? Especially since they have a lengthy head start on you!

I have never seen an XPS system in either of the large hobby shops here - but I can tell you the Spektrums go out the door faster than props......

I tried to get Steve to tell me how many they have sold - he would not say, but I can say even they were surprised!

But no question to your point that 2.4GHz technology has become well entrenched in the hobby - a great think for us!

Mike
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Old Jul 06, 2007, 01:04 PM
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Gordito Volador's Avatar
Tampa, FL
Joined Apr 2003
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I love bright sales forecasts, especially when manufacturing can ramp up to meet demand.
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Old Jul 06, 2007, 03:35 PM
Proud to eat Kraut ;-)
Julez's Avatar
Germany
Joined Dec 2003
5,374 Posts
Quote:
Originally Posted by dick hanson
I might have to question this -
On my test bench - looking at servo performance with batteries commiting suicide -
the actual servo abilities to move depend on the servo LOAD.
some would stall and voltage went flat - IF the stick was held over - it all simply went in the toilet .
I was doing servo/battery exams at the time- the rx was then -a JR PCM
My conclusion was that dead batts are dead batts once you pass the knee in the cell discharge curve.
anything with over a tiny amp draw administered the Coup'
Ahhhhhhhhhhhhhhhhhhhhheeeee you die ! Yankee pig
(a little dramatic )

Gentlemen - we are not talking about dead batteries here. They cause crashes regardless which RC system we decide to use. Once again:

Low voltage because of dead batterys is not the problem.
Low voltage spikes because of load peaks are the problem.

There are load peaks in every plane. Some battery packs and switch harnesses are affected more by them, some less.
It all boils down to the internal resistance of the voltage source. This is the determining factor of how much voltage drop one will have with a given load.
The thing is: The lower the voltage, the smaller the current. It is Ohm`s law.
When the voltage will become low enough, the servos will stall and hardly draw any current any more. This means, even with the worst battery and switch harness, the voltage will never drop below the point where the servos are stalling because the load, that caused the voltage to drop, is not applied any more in this case.
In fact, it is a kind of control loop:

Load increases-->voltage decreases-->load decreases-->voltage increases.

When using a normal battery pack, one will never be likely to experience a voltage drop so severe that ist leads to a permanent servo stalling. But, it might be possible to have voltage drops that go quite deep.
In fact, when a servo begins to move, it draws the blocking current for the split second it takes the motor to begin to turn. Once the motor turns, the current is considerably lower.
This means, that a pack can be totally appropriate for operating all servos - but the voltage will still drop in this tiny split second where the servo draws the maximum current, as the motor begins to turn.

Now, we come to the critical part: How will a reciever react on these voltage drops, which are inevitable concerning the nature of batterys and Ohm`s law?

We learned, that the battery voltage can never fall beyond the stalling point of the servo - if this was the case, no servo would move in the first place, and this would be suspicious even to the sub- average modeller.

For best safety of the complete RC setup, one would want a reciever that locks out at a voltage so low, that this level is never likely to occur.
As the servo stalling level is at about 3.1V, and the voltage cannot be any lower, the best reciever would only lock out when this level was undershot.
Futaba Fasst recievers lock out below 2.6V.
This way, Ohm`s law works like a safeguard that lowers the load to a value where the voltage will not longer decrease. This happens at a level where the voltage is still above the level where the RX would lock out.

Spektrum recievers, however, seem to lock out at 3.5V.
This is a voltage leven that one is much more likely to experience in an RC setup, as it lies above the servo stalling voltage. In fact, this level can be reached when having a battery that normally does just fine in powering the servos.
I have read about many Spektrum lockouts, where the pilot was able to move the servos in the remaining plane wreck. Low voltage because of a flat battery can thus not have been the cause of the crash.

To me, using a reciever, which is safeguarded against lockouts by Ohm`s law, offers the following benefits:

- The only concern I must have when choosing batterys, is the capacity. Of course, a low internal resistance is a valuable quality, too. But I will never loose my plane just because my batterys do not hold the voltage too well under load.

- Mr. Ohm will protect my plane in the case of one dead cell in a 4-pack. 3 cells will sustain 3.6V normally. Voltage drops will be lower now, but my attention will be caught by slower servo movements, and not by faster plane movement (finally stopped by ground impact).

- I will be able to use singe LiPoly or LiIon cells in my planes. When every gramm counts, this is an important feature for DLG pilots.

Cheers,
Julez

PS: FASST reboot time: 0.9s
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Old Jul 06, 2007, 04:01 PM
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Sunnyvale, CA, USA
Joined Apr 2000
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"But I will never loose my plane just because my batterys do not hold the voltage too well under load."

Try it! You may, or may not, get lucky. There are far too many variables involved and it's dynamic rather than static situation. As the volts are heading south the device in question shuts down when its internal rails fall below whatever the local threshold is and will be following the battery with a delay or lag set by the local storage/regulation arrangements. The particular combination of servos battery and receiver may be benign...........or not.
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Old Jul 06, 2007, 04:15 PM
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dick hanson's Avatar
slc ut
Joined Nov 2003
867 Posts
Nicely written
The problem however is that the low voltage spikes are going to happen especially with high power output servos
You keep mentioning on a system which works down to below 3.5 volts
This is below design voltage on ANY 2.4 setup . To be exact- 4.8 setups do allow some error but 4.8 v batteries are quite low on remaining voltage once they drop to 4.8 with no load.
Why ? common setups are for 4.8v to 6 v in our models.
I don't know which servos you are using or the application - everything I have starts as a 4.8 volt device. Trying to gauge remaining power by slowness of servo operation is quit a risky method.
I have no concern at all about whether or not my system resets at 3.7 0r 3.5 or 3.3 or 3.1. These are levels of voltage so far down the usable battery levels of my chosen setups - I simply do not even consider it a problem
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Old Jul 06, 2007, 04:41 PM
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Daemon's Avatar
Lakewood, Colorado
Joined Aug 2002
29,109 Posts
Quote:
Originally Posted by JimDrew
Not the XtremeLink system. Our low voltage threshold is 3.2 volts. Any voltage lower will cause the receiver to reboot. Our complete reboot and re-acquistion time is 82ms... hands down, the fastest of any system available.
One little correction here. 3.2 volts to the CPU itself may be where it resets,
but my testing shows that that is aprox 3.7 volts external with XPS.
Dunno where the other 0.5 volts is going, but it definitely starts
resetting when voltage drops below 3.7, as measured across the
battery wires. As you well know, I've got video of an oscilloscope screen
showing it.

As for whether it just resets and continues on with reduced response,
or the servo glitches after reset (several do), which causes another
current spike and voltage drop causing it to reset again, and again,
continuously.. depends on the servo.

ian
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Old Jul 06, 2007, 08:00 PM
You can call me FANBOY!
Goodlettsville, TN
Joined Sep 2006
3,058 Posts
Quote:
Same here- the DX7 radios reproduced like wabbits and if there are unhappy users -I simply have NOT heard of them here.
From what I have seen here and else where it appears to me that you simply choose to ignore them. I used to work with a guy like you, he was the server mgr in the IT department I worked in for a large company. Whenever we would approach him with a problem his response was always "I have never had a problem with that." Never mind the favt that we had it documented that multiple users were experiencing it he hadnt seen it so therefore it wasnt an issue. May work great in your world but tell that to the guys who have lost planes due to low voltage resets and uncommanded control inputs and lockouts.
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Old Jul 06, 2007, 08:03 PM
You can call me FANBOY!
Goodlettsville, TN
Joined Sep 2006
3,058 Posts
Quote:
And what brand do you recommend? Maybe the Futaba will be the cure all.
I use XPS! And I will let that speak as to what I trust. Not to say that I would distrust Futaba, quite the opposite. But I am not willing to pay the premium that they command just to get the Futaba name.
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Old Jul 06, 2007, 08:23 PM
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dick hanson's Avatar
slc ut
Joined Nov 2003
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Ther are two shops in our city - (SLCUtah) -which sell em-- I know the people and I fly at the State Park which has th largest number of flyers . If there were some unhappy folks -I would have heard about them . There may be some - but they have not shown up anywhere most of us fly.
Are the systems perfect?
beats me but .they certainly are popular .
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Old Jul 06, 2007, 08:34 PM
You can call me FANBOY!
Goodlettsville, TN
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So were Chevy Vegas, at least for a while. And its not about being perfect, its about being the least flawed.
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Old Jul 06, 2007, 11:47 PM
Xtreme Power Systems
Lake Havasu, AZ
Joined Jun 2005
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Quote:
Originally Posted by Daemon
One little correction here. 3.2 volts to the CPU itself may be where it resets,
but my testing shows that that is aprox 3.7 volts external with XPS.
Dunno where the other 0.5 volts is going, but it definitely starts
resetting when voltage drops below 3.7, as measured across the
battery wires. As you well know, I've got video of an oscilloscope screen
showing it.
I can guarantee it doesn't reset until 3.2 volts. I have hours worth of testing just on this feature, which is something that I deliberately designed into the system.
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Old Jul 07, 2007, 02:17 AM
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Daemon's Avatar
Lakewood, Colorado
Joined Aug 2002
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Quote:
Originally Posted by JimDrew
I can guarantee it doesn't reset until 3.2 volts. I have hours worth of testing just on this feature, which is something that I deliberately designed into the system.
That's odd because according to both my voltage meter and my oscilloscope,
it resets at 3.7 volts or thereabouts. Even during the continuous reset
cycle it still never drops below 3.6 volts.
http://www.thud.us/videos/rc/xps-low-bat-test4.wmv
Has something changed in the later Rx's since I made that video?

BTW, I remember where I first heard that 3.7 volt number mentioned.
Twas you, twice.
http://www.rcgroups.com/forums/showt...+7#post7445237
http://www.rcgroups.com/forums/showt...+7#post7445331
My own tests just confirmed it.

ian
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Old Jul 07, 2007, 03:42 AM
Valid8r
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Boston and Belgium
Joined Jul 2004
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I hate threads that start and the originator never makes a final comment so let me say that as the originator, my questions have been more than adequately answered. My take home message is the following:

For most of the park flyers (loosely defined as those persons flying 4 servos, less than approximately 48oz planes, using decent Lipos and decent ESC's (read CC for me)) that the problem of low reciever voltage problem should not be an issue.

This also makes sense to me as the overall weight addition of the 4 or 5 cell Rx battery pack would severly impact the ability of most park flyers to even get into the air and sales of 2.4GHz systems contradicts this.

Despite the fact that I like the Futaba radios (from what I've heard and read), and I want to support the new guy on the block (XPS), for now I will stick with the gift my loving wife gave me (a new radio was a lot more logical to her than trying to find room in the basement for another plane) and try out my new DX7.

I thank you all for the help, advice and useul information. I wish you all good luck and fun in the ongoing debate.

Sincerely,
Jon
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Old Jul 07, 2007, 04:22 AM
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Christchurch, New Zealand
Joined Jun 2006
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I'd like to add to that: there's a new crop of ESCs coming out with switchmode BECs, especially medium sized ones. These are ideal for something like a T-Rex or the large end of parkfliers, which use a bit more power under load, enough to get something like a CC35 in trouble. I highly recommend using them with 2.4GHz radio systems.
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