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May 07, 2019, 08:14 AM
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Powering servos


I'm having a problem with my servos. When i move them slowly everything is fine. But if i move them quickly, they kind of stutter and eventually stutter their way to where i commanded them. I can move one servo any speed no problem but two makes this happen. If i move all of them it happens much sooner. So i guess it is insufficient power. I have a bec and tried that with the same results. Changed receiver; no change.
My setup (that would be handy!):
Hitec optima 7 receiver.
Red brick 100A esc.
Futaba s3003 servos. There are 4 of them and i doubt they are legit!
I am using a power meter but it is measuring the overall voltage, power etc. It shows 0.28A with just the elev servo moving quickly. The 2 aileron servos bring it to 0.4A approx. That stays the same when i move them slowly. They work fine slowly too.
Also, i unplugged the ailerons and moved the elevator and rudder quickly with the same stuttering happening.
This same setup was transferred from another plane i have, with the exception of the servos. Is there something else happening here, rather than power?
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May 07, 2019, 09:44 AM
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coriolan's Avatar
The "Red brick" BEC is most likely the weak link in your system, specially with 4 servos if more than 7.4 V Lipo!
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https://cdn-global-hk.hobbyking.com/...anual_ok_1.pdf
May 07, 2019, 11:29 AM
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Thread OP
Thanks for the reply. Yeah, i'm suspecting the red brick alright, but i tried a seperate ubec or bec and it did the same. The only things different here are the servos. All else was transferred from another plane that flew fine. Its a weird one alright!
May 07, 2019, 12:25 PM
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coriolan's Avatar
What kind of voltage are you using?
May 07, 2019, 02:01 PM
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Thread OP
Ah yeah! Another vital bit i left out!
4s battery.
The transmitter was briefly alarming at what i can only assume was low voltage to the receiver. I'll set the alarm voltage a little higher to prove/disprove this a bit.
May 07, 2019, 02:08 PM
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Miami Mike's Avatar
If you have a 4-cell NiMh pack, plug that into an open receiver servo channel and unplug the ESC and/or the LiPo pack. That will tell you if the ESC is causing the problem.
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May 07, 2019, 02:14 PM
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Thread OP
Thanks for the help guys! I have family commitments to endure first. Do they not realise i have a plane to get flying!!
May 09, 2019, 11:59 PM
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vollrathd's Avatar
Quote:
Originally Posted by diggerkelly
I'm having a problem with my servos. When i move them slowly everything is fine. But if i move them quickly, they kind of stutter and eventually stutter their way to where i commanded them. I can move one servo any speed no problem but two makes this happen. If i move all of them it happens much sooner. So i guess it is insufficient power. I have a bec and tried that with the same results. Changed receiver; no change.
My setup (that would be handy!):
Hitec optima 7 receiver.
Red brick 100A esc.
Futaba s3003 servos. There are 4 of them and i doubt they are legit!
I am using a power meter but it is measuring the overall voltage, power etc. It shows 0.28A with just the elev servo moving quickly. The 2 aileron servos bring it to 0.4A approx. That stays the same when i move them slowly. They work fine slowly too.
Also, i unplugged the ailerons and moved the elevator and rudder quickly with the same stuttering happening.
This same setup was transferred from another plane i have, with the exception of the servos. Is there something else happening here, rather than power?
I did a LOT of testing on this very subject a year or three ago. These tests are posted in RCGroups. The last posting on the Arduino Nano VoltSagger project is installed on every one of the models I'm currently flying. This meter measures the voltage 5000 times per second, and displays the lowest voltage ever reached during your flight.

The problem is these servos do not pull simple DC current, but rather a repeating pulse current that hits 3 Amps, 45 times per second. Your meter shows average current, and can not display those peak currents. I have a digital meter that can, but it is a $350 Fluke 87V meter.

That VoltSagger project identified a big problem with my giant TurboBushmaster whose radio/servo system is powered by a Castle Creations 100 Amp ESC with its built in ESC. That receiver voltage was dropping below 4 Volts when the BEC was programmed to 6.5 VDC.

Solution was to install a separate Castle Creations 10 Amp BEC that took care of the problem. That CC BEC can handle brief 14 Amp peak currents, yeah I checked it with one of my oscilloscopes.

If you are flying with glow or gasoline, an option would be to go to a two cell 2500 A123 receiver pack. These cells do not sag in their voltage output with the currents pulled by the typical RC receiver system. I use those A123 battery packs as backup to the BEC's on my three giant scale models with their 2200, 2800 and 4500 Watt power systems. I can provide wiring on how to do that.

Analog and Digital Servo Tests
http://www.rcgroups.com/forums/showthread.php?t=2433116

Rant on using 4 cell Nih Packs
http://www.rcgroups.com/forums/showthread.php?t=2431435

Arduino Nano Voltsagger
https://www.rcgroups.com/forums/show...t#post40495307
May 12, 2019, 09:05 AM
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Thread OP
Thank you! I've been busy with other stuff lately so hopefully i'll get back to this during the week.
May 25, 2019, 03:56 AM
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RCvertt's Avatar
Quote:
Originally Posted by diggerkelly
...When i move them slowly everything is fine. But if i move them quickly, they kind of stutter and eventually stutter their way to where i commanded them. I can move one servo any speed no problem but two makes this happen...
Sounds like a problem I ran into. I was using one 3 amp bec. As others have said, the solution was to use two bec's instead of just one.

BadServoMovement (0 min 29 sec)
May 25, 2019, 07:32 AM
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vollrathd's Avatar

Paralleling. BEC's


Paralleling switch mode BEC's is never a good idea. It might work, but can result in unreliable operation.

Here is a direct quote from the Castle Creations Web page.

"Note: CC BEC's should never be operated in series or parallel with another BEC or backup receiver pack connected to the RX/Servo side of the circuit.
"


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