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Voltage drop and the dreaded "Brownout" , What's really at fault ?

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Voltage drop and the dreaded "Brownout" , What's really at fault ?

Old 09-24-2015, 01:08 PM
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BarracudaHockey
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Digital servos have their advantages and their place. If you're flying 3D, jets, or where precision, holding power, and repeatable centering are premium, then you're probably going to want digitals.

As for power systems, other than review planes that come with batteries, I use A123's wherever possible.
Old 09-24-2015, 02:01 PM
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dirtybird
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Several years ago I did some servo testing for RCU that was never published due to a stupid presentation mistake on my part. Analog servos have a deadband of about 13us, digital servos with a three pole motor are usually about 5us and digitals with a coreless motor are typically about 3us. The JR 8411 was advertised at the time at 0us deadband. My tests revealed that that was in fact true. That meant the servo had no resting place. It was continually in motion and drawing current. This would wear out the gears. There is a fellow flier(a top IMAC flier) in my club that uses them or its replacement. He sends his servos to JR every year to be refurbished and a gear change. If you want ultimate return to a spot you have to pay for it.
Unfortunately the 8411 has a fairly linear transfer function. I prefer a servo that gives more torque at a smaller error signal. For that the Hitec 5995 is best. I prefer it even though it is a 180 deg servo.
I have not tested later servos so I have no data on them.
Old 09-24-2015, 02:33 PM
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Originally Posted by ackroyd View Post
What a great thread, full of very useful info and without the degradation into whinges and belittling certain radio brands. Thanks, great points on digital servos pulling the voltage down.
jmiles1941 is a great friend. He has the latest and greatest SERVO PROGRAMMER...He gave me his old one. Take his advice and get one. But only if you fly large 3-D aircraft. I love mine.

Do you remember the Giant Futaba servos? I have them in my 155" cub. Only one per control surface...However, today we use multiple servos that are 300in oz of thrust. As my friend said...We are a lot safer doing that. I just put Dual Spektrum AR-7000 receivers n my 111" Extra 260. We use mainly LIFE for power and an Eq-10 when I can afford it. The red one is perfect for airplanes up to 50CC.

You can get a digital voltage monitor for only $10.00 . Well worth the price.
Old 09-24-2015, 02:39 PM
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Originally Posted by dirtybird View Post
Several years ago I did some servo testing for RCU that was never published due to a stupid presentation mistake on my part. Analog servos have a deadband of about 13us, digital servos with a three pole motor are usually about 5us and digitals with a coreless motor are typically about 3us. The JR 8411 was advertised at the time at 0us deadband. My tests revealed that that was in fact true. That meant the servo had no resting place. It was continually in motion and drawing current. This would wear out the gears. There is a fellow flier(a top IMAC flier) in my club that uses them or its replacement. He sends his servos to JR every year to be refurbished and a gear change. If you want ultimate return to a spot you have to pay for it.
Unfortunately the 8411 has a fairly linear transfer function. I prefer a servo that gives more torque at a smaller error signal. For that the Hitec 5995 is best. I prefer it even though it is a 180 deg servo.
I have not tested later servos so I have no data on them.
Hi-Tek Servos are what we all use. The 645MG for 60 size and the 5995 for the big ones. the next size down is $40 less and has plenty of torque..I use those most of the time. 1941 only uses the best...I love that guy..and his fiance. Great Christian Lady.
Old 09-24-2015, 03:59 PM
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deadstickdan
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So, is the official verdict on the battery power for Spektrum receivers to be run on 6v or will a .40 size plane, such as what i'm finishing now. which is using only 4 HiTec HS322HD servos run on 4.8v okay without worrying about power issues? I have only used Futaba and never used Spektrum before. The new Spektrum module I have is mounted in an older radio and the receiver is the AR610 which I just purchased.

Last edited by deadstickdan; 09-24-2015 at 04:12 PM.
Old 09-24-2015, 04:33 PM
  #31  
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Originally Posted by deadstickdan View Post
So, is the official verdict on the battery power for Spektrum receivers to be run on 6v or will a .40 size plane, such as what i'm finishing now. which is using only 4 HiTec HS322HD servos run on 4.8v okay without worrying about power issues? I have only used Futaba and never used Spektrum before. The new Spektrum module I have is mounted in an older radio and the receiver is the AR610 which I just purchased.
deadstickdan I would run 6 v on all and you shouldn't have any problems just my thoughts and I use hitrc 7955 titanium gears my 42% extra weighs 40 lb

Last edited by jmiles1941; 09-24-2015 at 04:42 PM.
Old 09-24-2015, 05:35 PM
  #32  
shooboy
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I fly most of my planes with my Spektrum DX8 and 4.8 volt Nimh Turnigy batteries on my smaller 40-size planes and the 6.0 volt Turnigy's Nimh on planes up to 1.20 size. Even running one on my Sig Rascal 110 with no issues. The only time I've had a problem was when a receiver sold to me as genuine Spektrum was a fake, and I lost my 43cc Ultimate Bipe because it failed. I sent the receiver to Horizon before I knew it was a fake and they sent it back saying it was not a Spektrum product. I am also just getting some good hours on my new JR XG8 DMSS and starting to switch over to LiFe receiver batteries. I'm flying a new Seagull iSport 10cc with an Evolution 10cc gas engine, and using inexpensive little Zippy 700mah LiFe's on the receiver and ignition. What a deal on those batteries, under $5 each and with me running almost all analog servos the little guys will last 4 flights with no issues at all. I'll eventually be switching everything over to LiFe's because of the consistent voltage and I'll probably going to buses for the servos on my bigger planes as some of you guys have suggested. I am very happy with both my new JR tx and my Spektrum DX8, I just had a meltdown about all the fake Spektrum receivers out there. I honestly believe that there are guys buying fake Spektrum AR9000's or whatever for $30 and selling them for $80 or $90 and passing them off as genuine. I see that somehow they are selling them in baggies or whatever and there's no original packaging. I will never buy one of those ever again, only stuff in real Spektrum packages. I see a lot of receivers for sale on RCGroups and they are as I said, no packaging and the sellers seem to have several week after week. Thanks and I appreciate all the info here, Shoo
Old 09-24-2015, 05:42 PM
  #33  
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Actually the AR610 can run on up to 9.6 volts based on whats stated in the manual.

If you were to separate the servos onto their own power buss, you could run the servo buss on 6 volts NiMH, since the HS322HD servos are 6 volt rated.. and then run the receiver on either 6.6 volt LiFe, or 7.4 volt Li-Ion... that would insure a good power supply to the receiver, with optimum performance and range... its just a suggestion... I would always power the receiver separately, that's just the way I think!




John M,

Last edited by John_M_; 09-24-2015 at 05:49 PM.
Old 09-24-2015, 05:53 PM
  #34  
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Originally Posted by shooboy View Post
I fly most of my planes with my Spektrum DX8 and 4.8 volt Nimh Turnigy batteries on my smaller 40-size planes and the 6.0 volt Turnigy's Nimh on planes up to 1.20 size. Even running one on my Sig Rascal 110 with no issues. The only time I've had a problem was when a receiver sold to me as genuine Spektrum was a fake, and I lost my 43cc Ultimate Bipe because it failed. I sent the receiver to Horizon before I knew it was a fake and they sent it back saying it was not a Spektrum product. I am also just getting some good hours on my new JR XG8 DMSS and starting to switch over to LiFe receiver batteries. I'm flying a new Seagull iSport 10cc with an Evolution 10cc gas engine, and using inexpensive little Zippy 700mah LiFe's on the receiver and ignition. What a deal on those batteries, under $5 each and with me running almost all analog servos the little guys will last 4 flights with no issues at all. I'll eventually be switching everything over to LiFe's because of the consistent voltage and I'll probably going to buses for the servos on my bigger planes as some of you guys have suggested. I am very happy with both my new JR tx and my Spektrum DX8, I just had a meltdown about all the fake Spektrum receivers out there. I honestly believe that there are guys buying fake Spektrum AR9000's or whatever for $30 and selling them for $80 or $90 and passing them off as genuine. I see that somehow they are selling them in baggies or whatever and there's no original packaging. I will never buy one of those ever again, only stuff in real Spektrum packages. I see a lot of receivers for sale on RCGroups and they are as I said, no packaging and the sellers seem to have several week after week. Thanks and I appreciate all the info here, Shoo
shooboy the fake recievers may be a large part of the spectrum problems , not being genuine Spektrum that would be a huge problem , sorry for your loss I guess there are people out there that will sell anything just to make a buck , really sad
Old 09-24-2015, 06:25 PM
  #35  
deadstickdan
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Okay, 6 volt it is and I appreciate the information very much. Better safe than sorry

Dan
Old 09-25-2015, 04:15 AM
  #36  
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^^^^ Exactly...spend a few $$$, go to 6v and be done with it.

FYI, I have one plane, a H9 Hellcat .60, that the gear servo would not work on 6v. It likes 4.8, and that's it. So, I rewired to run that servo with it's own dedicated 4-cell 4.8v NiCD pack. In the overall scheme of things, this has the added benefit in that the gear servo cannot drain down the main battery pack. Plus, I needed a little nose weight anyway!
Old 09-25-2015, 05:35 AM
  #37  
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Just wondering. If I wanted to run a dedicated receiver battery. From what I have chrecked the amp draw for the reciever really small. So could I use a lets say 500mah lipo or life. and run a larger battery 2500 or larger to run the servos on a servo city power board? All I have is Spektrum equipment. I am just trying to make my flight packs as robust as possible with economy in mind. And would it make sense to use a Deans connector for a switch instead of the standard small gage wire switches to power my servo city board.

Thanks
Old 09-25-2015, 06:33 AM
  #38  
dirtybird
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yes

You do not want to get the two batteries in parallel. So just bring the signal wires over from the receiver to the power board. Then tie the negative wires of the two batteries together.
PM me if you need to know how to do that

Last edited by dirtybird; 09-25-2015 at 06:43 AM. Reason: more info
Old 09-25-2015, 07:26 AM
  #39  
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Dirtybird

Thanks for the reply. I understand about keeping the batteries separate so one does not bring down the other in a bad situation. i did not think about putting the 2 negatives together though. I thought that using a smaller mah battery will help for room if you want to put your mind at ease in smaller aircarft. Also what do you think would be a safe mah for the reciever? they make some really small high c rating lipos. that might work really well. Do you think that i would have to regulate a lipo for a spektrum reciever?

Does anyone make a balance connector that can be mounted outside of the aircraft? This would work out well to do a battery check without removing the hatch.

Thanks
Old 09-25-2015, 07:28 AM
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Batteries won't take each other out despite the popular rumor spread by folks selling battery isolators
Old 09-25-2015, 07:38 AM
  #41  
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Originally Posted by rcyoucando View Post
Just wondering. If I wanted to run a dedicated receiver battery. From what I have chrecked the amp draw for the reciever really small. So could I use a lets say 500mah lipo or life. and run a larger battery 2500 or larger to run the servos on a servo city power board? All I have is Spektrum equipment. I am just trying to make my flight packs as robust as possible with economy in mind. And would it make sense to use a Deans connector for a switch instead of the standard small gage wire switches to power my servo city board.

Thanks
Go with a larger capacity than 500 mAh, if you fly several long fights, you don't want to fly with the battery below two thirds of it capacity... its like driving you car 300 miles with only half a tank of fuel, why risk it... I fly my receivers on a 2300 mAh 6.6 volt LiFe, and recharge after the third flight.



John M,

Last edited by John_M_; 09-25-2015 at 07:42 AM.
Old 09-25-2015, 08:23 AM
  #42  
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My XPS 6 channel receiver draws 60 ma with no servos connected and receiving signals. A 500mah battery should last up to 8 hours. I don't expect a Spektrum would draw much than that. You should check with Spektrum. Check also the voltage tolerance.
You definitely never want two different capacity batteries in parallel.
If preventing brownout is the object it wouldn't make much sense to do so.

Last edited by dirtybird; 09-25-2015 at 08:25 AM. Reason: correct typo
Old 09-25-2015, 08:29 AM
  #43  
dirtybird
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Originally Posted by BarracudaHockey View Post
Batteries won't take each other out despite the popular rumor spread by folks selling battery isolators
If a battery shorts out it will definitely take the other one down.
Old 09-25-2015, 10:02 AM
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Dirytbird

That is only if you have them in a paralle not separated by the power board and only hooking the negatives together correct?
Old 09-25-2015, 10:09 AM
  #45  
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Hello All,


Like what has been mentioned earlier about batteries and would like to add my experience and experiment.


I have a Lanier Yak-54 87" with a 3W-75i.
Engine has it own switch and battery.
Wing servos, four Hitec 645mg
Elevator, two Hitec 645mg
Rudder, one Hitec 5755mg
Receiver JR 9ch PCM
Switch harness, JR heavy duty
Battery, Hangtime Hobbies 2300Mah A123 dual line EC3 and heavy duty JR (only JR end used in this first set up)
Voltmagic battery monitor and logger.


I flew this airplane a long time. The voltmagic never logged a voltage drop even when working the servos hard back and fourth.


Then I decided to purchase a 2.4Ghz radio set up. I decided to try it in this airplane. The only thing I did was swap out the receivers. While doing pre-check outs so far I noticed no problems. I proceeded to work the servos by doing the hard back and fourth test for a couple of seconds simulating high current draw. Bam voltmagic logged a voltage drop. Crude. I verified the battey was full charge (also tested the battery on a Power Lab 8 charger, tested OK) and tried the test again. Voltmagic logged another voltage drop at the receiver.


I happen to have one of Hangtimes heavy duty switch harness. The one that has dual in (EC3 and heavy duty JR) and dual out (two heavy duty JR). The only thing changed was the swap from the JR heavy duty switch harness to the Hangtimes hobby switch harness (Electro Dynamics). Voltmagic has never logged another voltage drop after the swap even while doing the test.


With the tools that I have I can only theorize that the 2.4Ghz received allow the servos to work harder (for some reason beyond me) and the limiting factor then became the switch harness for the amperage draw.


What I learned is to test voltage drop at the receiver.
Old 09-25-2015, 10:49 AM
  #46  
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Originally Posted by BarracudaHockey View Post
Batteries won't take each other out despite the popular rumor spread by folks selling battery isolators
Originally Posted by dirtybird View Post
My XPS 6 channel receiver draws 60 ma with no servos connected and receiving signals. A 500mah battery should last up to 8 hours. I don't expect a Spektrum would draw much than that. You should check with Spektrum. Check also the voltage tolerance.
You definitely never want two different capacity batteries in parallel.
If preventing brownout is the object it wouldn't make much sense to do so.
Originally Posted by dirtybird View Post
If a battery shorts out it will definitely take the other one down.


The two battery packs are isolated from each other through the servo buss... only the negative / ground is common (carried through), so the two different chemistry's and voltages / capacities wouldn't interfere with each other.

Certainly a 500mAh pack would be sufficient to power the receiver with a continuous 60 mAh draw, but my point was I personally would not fly with a battery below 2/3 charge capacity... anyways a 2300 mAh 2 cell, A123 6.6 volt LiFe pack weighs about the same as a 500 mAh 4.8 NiCad / NiMh pack does... and besides a little extra battery capacity never hurt anything.

I have a 5 sub "C" cell, 6 volt, 3000 mAh NiMh pack on the servo buss, and a 2 cell, 6.6 volt A123 / 2300 mAh LiFe pack powering the receivers... I could probably fly 6-8 15 minute flights back to back, or more with that setup without recharging; would I do it, absolutely not... the max I'll go before topping up the batteries is, maybe 4 flights... might as well take advantage of the time while I'm chit-chatting with the guys in the pits, I'm topping up the batteries... am I being overly cautious, or being too annal, you're damn right I am, I wouldn't have it any other way



John M

Last edited by John_M_; 09-25-2015 at 11:17 AM. Reason: Corrected spelling / grammar
Old 09-25-2015, 10:50 AM
  #47  
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My experience agrees with the fact that digital servos are very demanding of dc current. When they initially start or if they are stalled the current demand is higher that 2000 MAH NiMH battery can deliver. Speckrum receiver will reset if their input voltage drop below 3.6 volts even for a millisecond. These are facts, I have measured them myself. As a retired Electronic Technician and a life long electronic hobbyist I have the skills and test equipment to back it up. Solution for me is LiFe battery and to build separate power source for the receiver and the servos. This avoids receiver voltage drops/resets.
Old 09-25-2015, 10:56 AM
  #48  
dirtybird
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Originally Posted by rcyoucando View Post
Dirytbird

That is only if you have them in a paralle not separated by the power board and only hooking the negatives together correct?
Yes
Old 09-25-2015, 11:00 AM
  #49  
dirtybird
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The two battery packs are isolated from each other through the servo buss... only the negative / ground is common (carried through), so the two different chemistry's and voltages /capacities wouldn't interfere with each other.

All of the receivers and power buses I have have both the plus and minus buss common.
Old 09-25-2015, 11:51 AM
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Having a separate battery for the receiver is certainly not a bad idea, but it probably is not going to make much difference if a servo shorts out and pulls down the servo bus voltage so low, that the good servos can't do the job. Your receiver may be fat and happy, but you're gonna crash anyway
Dirtybird,
Many years ago I had a cell short out in a 4 cell Nicd pack. Those old Airtronics 94102 servos were noticeably sluggish, I landed posthaste!
That's when I switched to 5 cell Nicds. Now I use LiFe/A123 in everything I fly.
Pete

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