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Direct 7.4V to servo

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Direct 7.4V to servo

Post by Neodymium09 on Sun 13 Apr 2014 - 16:04

Hi laneboysrc,

Need your advise and confimation on hooking up direct 7.4V to servo.
Is the image sketch correct? Should I connect the GND of servo to the ESC out or Rx out?

Thanks!


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Re: Direct 7.4V to servo

Post by laneboysrc on Sun 13 Apr 2014 - 20:26

Hi!

The diagram is basically correct, but can be improved.
In theory you could connect the ground wire (black or brown) from the servo to either A or B, but your original connection A is not preferred as it would require you to hack up the servo wire from the ESC to the receiver.

So either use connection B, or you can also connect it to the black wire coming from the battery. Then you would run 2 wires from the servo to the battery, and one to the receiver.

See changed drawing attached. Personally I would go for A since you need to splice up the servo cable anyway. But it all depends where the items are located and how easy it is to do the soldering.


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Re: Direct 7.4V to servo

Post by Neodymium09 on Sun 13 Apr 2014 - 20:48

OK bro,
I got it. So basically leave the other connections as is, but red power and black ground connected such that esc and servo is in parallel across the lipo out. Only leave signal wire of Rx to servo intact.. Thanks! Will hook it up this week..  Smile 

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Re: Direct 7.4V to servo

Post by Neodymium09 on Mon 14 Apr 2014 - 10:28

Ok quick update,
Connected with DIY Y-Cable+Deans connectors to connect servos in parallel to ESC across the Lipos. Working fine.  Very Happy Thx Werner.

Tried 3 more alternative that doesn't work;  Mad 
1. Direct attach servo to Rx as normal connection. Glitchy motors when HV servo is in operation.
2. Use separate batts for servo and retaining signal from receiver. Totally no response from servo even checked voltage into servos was around 7.5V.
3. Attached separate battery to receiver free channel. Glitchy operation. Probably due to Rx is 6Vmax rating but batts into free channel is 7.5V Lipos.

Anyone knows of alternate receiver compatible with Axial transmitters? Other methods might be able to work if receivers were rated up to 7.5V.

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Re: Direct 7.4V to servo

Post by laneboysrc on Mon 14 Apr 2014 - 10:43

Glitchy operation usually means that the high current draw from the servo causes the voltage to drop. For example the over current protection of the BEC may be triggered, causing a temporary drop in voltage.

Separate batteries: For this to work you must connect both ground (black) wires of the batteries together. Then it should work fine.

Do not put more than 6V in the receiver, the voltage regulator in there may get permanently damaged.
I think the Axial receiver is a OEM FlySky receiver. HobbyKing has a cheap alternative one, but also only up to 6V.

The receiver is actually a bit special as it has a built-in "boost converter" for 1S direct operation (from what I can see in the circuit, there is not spec about that)

I can modify the receiver for you by changing the voltage regulator and a capacitor, and taking out the boost circuitry. The mod will allow you to directly put up to 10V max into the receiver, i.e. directly use it with a 2S LiPo. Disclaimer: I've done this mod successfully with several HobbyKing XR3000 receivers, but not yet with FlySky; so there is a (low) risk.

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Re: Direct 7.4V to servo

Post by RTECH on Mon 14 Apr 2014 - 19:19

Very Happy 10v into receiver sounds great ! No more worries about using lipo on esc without bec.

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Re: Direct 7.4V to servo

Post by laneboysrc on Mon 14 Apr 2014 - 19:21

RTECH wrote:Very Happy 10v into receiver sounds great ! No more worries about using lipo on esc without bec.

Indeed! Not only is it useful for HV servos, but also when you have old Tamiya ESC like the TEU-101BK or TEU-104BK without BEC. I run such setup on our M05, M06 and Cup Racer.
Better change a $0.20 voltage regulator than throwing away a mediocre ESC Smile

I'd be happy to do the mod for locals. No cost involved, but your risk if I blow up the receiver  Embarassed

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Re: Direct 7.4V to servo

Post by boolean21 on Mon 14 Apr 2014 - 19:30

Awesome gesture from our electronics guru!
 Twisted Evil Twisted Evil Twisted Evil 

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Re: Direct 7.4V to servo

Post by Neodymium09 on Tue 15 Apr 2014 - 17:06

Thanks werner,

Sounds good to try. But let me look-up and find and stock up on the compatible receivers first as you suggested from Hobbyking before meddling with the existing ones.. hehe.
Very good educational thread here  Very Happy 

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