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Old Nov 03, 2010, 06:04 PM
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planefun's Avatar
South Central PA
Joined Oct 2003
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Question
LiFeP04 receiver pack and servos

Hi everyone,

Iím using the LiFeP04 1450 6.6 volt receiver battery in my plane. I switched from 5 cell 2/3 batteries about 5 months ago. My plane has JR 368 servos all the way around. In the last 3 months 3 servos have stopped working on me. One stab servo, rudder and flap. Could the voltage of the LiFe batteries be causing the servos to stop working? The 5 cell NiMH batteries were about the same voltage fully charged. Should I change my servos in order to accommodate the new battery pack? Any suggestions?

Thanks for reading.
PF
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Old Nov 03, 2010, 06:33 PM
Eggcellent...
tewatson's Avatar
United States, CA, Orange
Joined Oct 2006
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FWIW, I have not noticed any abnormal servo behavior with either LiFe or A123 packs over the past year. Might be a coincidence.

Tom
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Old Nov 03, 2010, 06:36 PM
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codezilla's Avatar
Chino Hills, CA
Joined Feb 2003
2,370 Posts
I've been using 2cell LiFe cells (A123) with JR 368 servos on two planes without any issues. Check to see if any of the surfaces are binding which could pull more current and burning up the servos.

Adrian
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Old Nov 03, 2010, 06:47 PM
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Silent-AV8R's Avatar
Orange County, CA
Joined Aug 2004
4,310 Posts
Same here. LiFePO4 in everything I fly for ove a year now without any issues, and I am running Futaba 3150 servos that are noted by FUtaba as 4.8 volt only. No problems.

As noted above, these packs make it critical to have no binding, etc. They do work at a slightly higher voltage than a Nimh, but more importantly they will deliver a higher voltage under a significant load way better than a NiMH. So if you are binding or stalling the servos at all they will die sooner. And as Tom said, it may be nothing more than coincidence, either that or the servos were close to EOL anyhow and the stronger packs nudged them over the edge a tiny bit sooner.
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Old Nov 03, 2010, 07:08 PM
mostly gliders
liukku's Avatar
SkellefteŚ, Sweden
Joined Sep 2003
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Very possible!

Quote:
Originally Posted by planefun View Post
Hi everyone,

I’m using the LiFeP04 1450 6.6 volt receiver battery in my plane. I switched from 5 cell 2/3 batteries about 5 months ago. My plane has JR 368 servos all the way around. In the last 3 months 3 servos have stopped working on me. One stab servo, rudder and flap. Could the voltage of the LiFe batteries be causing the servos to stop working? The 5 cell NiMH batteries were about the same voltage fully charged. Should I change my servos in order to accommodate the new battery pack? Any suggestions?

Thanks for reading.
PF
Hello planefun

To answer your question, "Could the voltage of the LiFe batteries be causing the servos to stop working?"

Very possible, perhaps too early to draw any conclusions yet, but it is known that many manufacturers specify their servos for only 4.8V-6V.
LiFe batteries are fairly new to be used to power our old types of servos. I have started using LiFe batteries but I use them together with a regulator. I am about to complete a 2 m Sprite Thermal. In it, I will only use Hyperion high volt servos. That way I will not have to use a regulator.

Read this post in the thread, "Using Lipo's in sailplanes" http://www.rcgroups.com/forums/showp...3&postcount=32 and you need not feel alone anyway.

/Ville
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Last edited by liukku; Nov 03, 2010 at 07:13 PM. Reason: adding info
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Old Nov 03, 2010, 07:22 PM
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tkallev's Avatar
USA, IL, Wheeling
Joined Jan 2003
3,122 Posts
It is far more likely you have some binding in the linkages and the servo is burning up the amplifier because it's trying to center all the time.

I have had no issues with 368s and 2 cell LiFePO4 packs.

tk
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Old Nov 03, 2010, 07:27 PM
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PDX Slope Pilot's Avatar
Portland, Oregon
Joined May 2002
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No issues here with 761z and DS3421 servos on unregulated LiFe packs.
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Old Nov 04, 2010, 12:52 AM
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Tuomo's Avatar
Jyvaskyla, Finland
Joined Aug 2003
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Quote:
Originally Posted by liukku View Post
Hello planefun

To answer your question, "Could the voltage of the LiFe batteries be causing the servos to stop working?"

Very possible, perhaps too early to draw any conclusions yet, but it is known that many manufacturers specify their servos for only 4.8V-6V.
LiFe batteries are fairly new to be used to power our old types of servos. I have started using LiFe batteries but I use them together with a regulator. I am about to complete a 2 m Sprite Thermal. In it, I will only use Hyperion high volt servos. That way I will not have to use a regulator.

5 cell nimh rx batts have been used for years. The big confusion over 3150s rose because DS368/3068 was known to be ok with the higher voltage but 3150 was specsed more like servo for 4 cell rx packs.

2s Life pack has lower voltage than 5s nimh pack. I would use them unregulated without doubts. Regulators have also some problems, so better avoid them if possible.
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Old Nov 04, 2010, 04:10 AM
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Warwickshire, England
Joined Sep 2006
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true, but I suspect LiFePo4 has a higher voltage under load (nimh drops voltage quite easily). I dare say most servos can take a high voltage under no load.

I am not sceptical about Life, I am just thinking about the difference under load.

I am thinking of trying LiFe in my next model with 2x 761s and 4 x graupner ds3288s, but I am not decided yet.

Tom
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Old Nov 04, 2010, 06:46 AM
mostly gliders
liukku's Avatar
SkellefteŚ, Sweden
Joined Sep 2003
960 Posts
Hello
It is "always" just a matter of time before anything breaks. Thats the nature of things. But as many Americans say, "each one becomes blessed in one's faith", no, that is not the saying, what is it? To each his own? nah...
"Like a bolt from the blue.", not sure.

/Ville
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Old Nov 04, 2010, 07:29 AM
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Tuomo's Avatar
Jyvaskyla, Finland
Joined Aug 2003
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Quote:
Originally Posted by satinet View Post
true, but I suspect LiFePo4 has a higher voltage under load (nimh drops voltage quite easily). I dare say most servos can take a high voltage under no load.
That is very true, but then again, things are not much more diferent if you use Life with (say) 6V 5A regulator, Futaba 3150 is still close to its limits.

Servos will allways burn sooner or later... I think there is no other solution to this dilamma than going to much more robust servos that run on higher voltage. Personally I would not mind flying this way, but we have also those guys in this forum who want to use the absolute smallest and lightest possible servo, to save a few grams in wing.
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Old Nov 04, 2010, 09:24 AM
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Orange County, CA
Joined Aug 2004
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As I have said numerous times, I am using 3150/3155 Futaba servos on unregulated 2S LiFePO4 with zero problems.

Beyond that, I have friends who have used the same servos on unregulated 5-cell NiMH without any issues. Futaba has a bad habit of being overly conservative on their servo ratings. However, real life results show that these servo are fine on both 5-cell NiMH and 2S LiFePO4 without a regulator.

As far as all servos eventually burning out, in 44 years in this hobby I have yet to burn up a servo. The most common reason for a servo going bad for me has been dirty pots causing a loss of centering and smoothness. The pot gets dirty enough and the servo becomes useless.
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Old Nov 04, 2010, 11:26 AM
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When it comes to batteries I love the speculation and opinion expressed on RCG all based on F.U.D. (Fear, uncertainty, and doubt)
Where is Tuan he knows batteries

sj
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Old Nov 04, 2010, 07:22 PM
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near Sacramento, CA
Joined Aug 2010
809 Posts
On diagnosing bad servos

"Quick" note on the subject of diagnosing dead servos on Lixx cell planes.

I just converted a plane to a Hyperion 1450mAh LiFe pack. Plane has 94761's in the wings and DS368's for rud and elev. Seemed to work fine for a few weeks, then started to notice the right aileron getting jumpy around center but also above and below center too. I thought it might be sensitive to higher voltage from the pack right off the charger so I did tests with inconclusive results. As it got worse I ended up replacing the servo which make the jumpy behavior a bunch better but not 100% gone.

Long story short, after much testing with servo and receiver swapping, looking at servo signals on an oscilloscope, swapping harness wires, etc. the problem turned out to be the servo harness connector at the receiver (ATK 10ch) not being fully plugged in (!). It was close but not all the way in. My point: other issues can cause symptoms that masquerade as a bad servo.

Moral of story for me: always bench test the supposed bad servo with a separate battery pack, wires, and receiver (if you can). When I finally did that, the "bad" servo ran just fine.

My .02 on the original post: three servos going bad so close together points to another problem. My guess: it could be due to a bad battery harness connection causing too much resistance somewhere in the battery wires part of the harness. It could also be defective wiring or connector in the pack itself. Either one could cause voltage to drop at the receiver and all the servos. That in turn could cause the current to rise to the servos esp. when they are moving, possibly causing damage. Just a guess. I'll be happy to suggest a few tests if you like.

Chris B.
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Old Nov 04, 2010, 07:23 PM
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planefun's Avatar
South Central PA
Joined Oct 2003
46 Posts
Liukku, that post is basically what happened to me. I use my Supra hard but I donít think there is any binding. The pushrods move very freely. Iím guessing launching hard could put stress on the elevator servo, since this is the servo that went out in mid flight. I really donít what to use a regulator. Regulators scare me more than battery servo problem. I would change the servos out but Iím not sure what to use for the flaps.

Iím in the process of putting a Pike together and would like to use the LiFe batteries. Any one make a high voltage flap servo that could take the place of a 368?

PF
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