Power drain? two servos and esc.

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limpet
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Power drain? two servos and esc.

Post by limpet »

I`m running a sabretooth together with two servos that operate as one.
When these servos are under strain the sabretooth stops operating, once they are moving again everything is ok.
Is there something I can do to fix this? the battery is a lipo 2s 120mah.
I can go to a higher mah on the battery as I`ve got spare weight if that might do it.
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razerdave
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Re: Power drain? two servos and esc.

Post by razerdave »

With only a 120mAh battery I am not surprised it's struggling!
Do you run the servos before the Sabretooth (running it off lipo voltage) or from the RX (5v)?
You definitely need a bigger capacity pack than that for 2 servos. 20mAh I would suggest.
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peterwaller
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Re: Power drain? two servos and esc.

Post by peterwaller »

The problem can be the battery as Dave says and I think he means to try a 200mah not 20.
But usually it is the fact that the 5v regulator on the sabertooth is only designed to supply around 100ma and the servo's could be taking as much as an amp or more each.
You could add a seperate 5V regulator that has a higher rating but you may still need a battery with a higher current rating.
While the higher capacity in mah is an indication you also need to look at the C rating as batteries do vary a lot.
My twin servo lifter is running from a 120mah nano-tech 25C battery quite happily but the regulator is rated at 1.5A.
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Re: Power drain? two servos and esc.

Post by razerdave »

Yeah, 200mAh. Oops :oops:
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limpet
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Re: Power drain? two servos and esc.

Post by limpet »

Thanks, I`ve got about 30g to play with so well within the scope of a bigger battery.
I`ve also asked at Dimension Engineering (the Sabretooth makers) and they have suggested if I don`t use the bec on the board I will need to disconnect the supply to the rx but how do I do that?
If I do supply the rx separately I`m assuming I just plug the battery into it? or is there something else I need to do with lipos.
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peterwaller
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Re: Power drain? two servos and esc.

Post by peterwaller »

First of all don't connect the receiver and servo directly to the lipo most are only rated at 5 or 6V.
I would think the easiest way is to leave the Sabretooth powering the receiver and just power the servo's from a extra regulator.
The regulator input would connect to the battery and the red power wire from the servo's should be disconnected from the receiver and connected to the regulator output as per below.
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limpet
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Re: Power drain? two servos and esc.

Post by limpet »

Thanks Pete that's brilliant. Do you know off hand of a part number for a suitable regulator? It will save me time as I`d like to have it fixed for Burgess Hill
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Re: Power drain? two servos and esc.

Post by BeligerAnt »

PM sent. :)
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peterwaller
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Re: Power drain? two servos and esc.

Post by peterwaller »

I use the LD29150DT50R Farnell No 156-4309 on my controller boards which are rated at 1.5A.
They cost £1.02 but you will need some decoupling capacitors on both input and output.
You can buy ready made BECs but I have never tried one of those.
Hopfully Gary has come up with a more straight forward answer.
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limpet
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Re: Power drain? two servos and esc.

Post by limpet »

Thanks for that Pete. Gary has sorted me out hopefully but it all helps.
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