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Servo voltage question

never tried this before

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Adrian Smith 116/11/2019 16:56:26
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Looking at some servos rates 4.8v - 6v on HK

**LINK**

Now if I wanted to drive then using a 7.2v 2S lipo would I need to buy a voltage regulator? Not tried this before to it may sound like a dumb question blush

Simon Chaddock16/11/2019 17:31:48
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Adrian

A 2s LiPo is 7.4V not 7.2 nominal and nearer 8,2V fully charged.

You would be operating the servo outside its specification voltage limit so if it failed it would be down to you.sad

Cuban816/11/2019 17:43:16
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Running direct from a 2S lipo is a no no. Quite clearly states a max of 6V. Being powerful 25-30kg servo it'll need a correspondingly decent power supply to feed it. Doesn't quote any figures for current in the specs, so you'll need to run a test from a power supply or large 4 or 5 cell Nimh and get some idea as to what current the servo is taking under full load with an ammeter, then choose a supply accordingly. A 3001 drawing a few hundred milliamps it ain't.

Edit.

A Test on YouTube shows a current of 6A. Stall current will be much more.

Edited By Cuban8 on 16/11/2019 17:59:32

Adrian Smith 116/11/2019 18:12:56
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Yes, Simon I realise I committed a typo on the 2S lipo voltage.

C8, as you realise I am looking to avoid a 6V nimh battery and indeed I guessed the higher voltage lipo would be inappropriate and you have confirmed that thanks. Basically I want adopt a simple answer such as this -

**LINK**

Unless you guys know better!

chris larkins16/11/2019 18:43:12
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Use a 2s LiFe battery, less volatile than a LiPo and the voltage drops to 6.6v once it is off charge

Martin Harris16/11/2019 18:43:59
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My preference would be to use 2S LiFe pack running through a silicon diode which will drop the voltage to around 6V.

That £23 regulator will only deliver 5A - a similar or better rated diode will only cost pence rather than pounds and should be at least as reliable.

Peter Beeney16/11/2019 23:06:08
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When the very first lithium polymer cells appeared on the scene a good few years ago they came as single units in an ali foil case and the two output tags; also fairly low capacity, as I remember. At first we couldn’t even get a charger for them, I used my bench supply and a voltmeter. It immediately occurred to me then that 2 cells in series might be very suitable for use as receiver packs. So I just cobbled a 6V 1A output regulator in the wiring, purposely left hanging free for max cooling, and lobbed it into a plastic drainpipe hack model. About 50 inch span and 5lb weight; Irvine 46 as motive power. 5 Futaba standard servos. After some heavy ground testing I flew it as hard as I could many times - the regulator never ever even got warm! Although in all fairness I have to say this was due to the very low input/output voltage differential, max 8.4 to 6V. Thus at best the reg. would only ever have to dissipate 2.4 watts of heat, (in theory anyway), definitely a not impossible task. However, I did abandon this idea sharpish when one of the cells went open circuit overnight; and indeed there were vague rumours this was happening occasionally at the time. Nowadays though, I’m certain this setup would be absolutely reliable, but I would use LiFe’s anyway now. 6V 1A regulators are as cheap as chips, so to speak, so it’s not an expensive mod to do.

Please don’t consider this to be any form of advice or instruction, it’s simply what I found when I was tinkering with it.

PB

Edited By Peter Beeney on 16/11/2019 23:08:33

Cuban816/11/2019 23:35:33
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Posted by Adrian Smith 1 on 16/11/2019 18:12:56:

Yes, Simon I realise I committed a typo on the 2S lipo voltage.

C8, as you realise I am looking to avoid a 6V nimh battery and indeed I guessed the higher voltage lipo would be inappropriate and you have confirmed that thanks. Basically I want adopt a simple answer such as this -

**LINK**

Unless you guys know better!

 

Only good for 5A according to the specifications. The YouTube review of the servo easily exceeded 6A. A good sized LiFe would probably be your best bet, but I'd still need some figures as to what the max current would be. You're going to need a hell of a good power supply with a few of those servos working hard. Keep RX and servo power sources separate as well. Just curious but why such a powerful servo?

Edited By Cuban8 on 16/11/2019 23:37:39

Adrian Smith 117/11/2019 09:26:42
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To cut a long story short C8 the reasons for wanting this type of servo are twofold.

I was using 5 Magregor HV servos (31.5kg.cms) in a 60cc airframe, using a 3.6A 2S lipo for RX power only, given the the HV Futaba RXs I have can cope with it easily. The performance was sparkling using servos with this power. I had used some HV Savox 20kg.cms servos in this aircraft previously, but performance was underwhelming. Recently I used the original Macgregor servos for another project therefore I wish to replace them at less expense in the original airframe. The problem as I stated is the disparity in voltage rating on the Turnigy servos compared to the separate RX batteries (2S lipos) I now use. I have had Turnigy equipment before and have no issues with it.

Hence asking the rather basic original question. I rather expected the substance of answers I received here and it just confirmed my thoughts.

cymaz17/11/2019 09:41:48
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Adrian, have you tried looking through THIS ?

I like the idea of the Powerbox item.

Edited By cymaz on 17/11/2019 09:44:31

Adrian Smith 117/11/2019 11:23:30
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Thanks, Cymaz. The only one that comes close is the Hitec 5955 TG at 24 kg.cms. The manual for the a/c in question recommends MKS HV -777A or HBL-380X8, but I don't have the budget for those assuming I can even get hold of them. The recommendations are +30kg.cms as can be seen from the servos' spec and there's a good reason for that suggestion from my experience.

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