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Author Topic: Servos at 6V  (Read 980 times)
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Madrid
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so i been working with some servos on an RC project i'm working on. and here is the thing most servos have 2 modes

Speed @ 4.8v:  0.21 sec @ 60 deg.
Speed @ 6v:  0.16 sec @ 60 deg.
Torque @ 4.8v:  3.3 kg.cm
Torque @ 6v:  4.1 kg.cm
(also seem some high speed servos that only work at 6V)

i would like to get them working on 6V using an separate battery for the servos, so i'm thinking in building a power distribution board for the servos, so i have a 2 cell 7.4v battery my first thought was to use a 7806 Voltage regulator but what will happen when the battery drops bellow 6v? i been thinking that maybe using a charging pump but most of them seem to be for 5/5.5V like the LTC1751, MCP1253, TPS61200.

so maybe i'm approaching this the wrong way, can anyone give me pointers to get in the right direction?

i may have to add i'm relatively new to electronics  (learning my way trough it now)
« Last Edit: December 06, 2012, 08:04:22 pm by lacion » Logged

Manchester (England England)
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You want to look at boost regulators for generating a higher voltage than the battery.
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Just keep in mind that each servo should have at least one amp of current available for it, so design your regulator(s) to support the max number of servos you wish to power at any given time.

Lefty
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Madrid
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ah thanks a lot Grumpy_Mike, i believe this could work http://www.pololu.com/catalog/product/791

retrolefty, i didn’t thought about the 1A, i will keep it in mind.

the attached image is the basic idea of what i thought, i may end up integrating the boost converter but i don’t see the necessity of it for now.


* servopowerboard.png (7.63 KB, 596x499 - viewed 7 times.)
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Most RC hobbiest use a UBEC like below to act as a power regulator. They are more efficient than linear regulators and have a 6v setting for supplying servos.

http://www.hobbyking.com/hobbyking/store/__3735__HXT_UBEC_5_6v_output_5_5_23v_Input.html
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Madrid
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yeah i saw thoose zoomkat, but that would remove the whole learning experience!
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I'm using a 3S Lipo for mine instead of 2S.  I had an extra one from my Parkzone P-51...

Like you, I didn't just want to plug in a BEC- I wanted to make one to learn.  I found a simple design that seems to be working well.  I have two 7806CT voltage regulators running in parallel.  On each side of the regulator I have a 10uf cap to ground.  Then the outputs go through a diode and then join before going to the servos.  I'm sure my lingo is incorrect. 

I found the schematic online and copied it.  The schematic ads two leds so you can tell if one isn't working becaues of overheating, but I didn't bother with that.  You don't get exactly 6V, but pretty close. 



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Oh, and I only used two regulators instead of 3 because each are rated at 1 amp, and I am only driving 2 servos.
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Oh, and I only used two regulators instead of 3 because each are rated at 1 amp, and I am only driving 2 servos.

Yes, it looks to be an effective circuit. But keep in mind that when a project is portable and battery based, duration of the batteries is an important and perhaps expensive goal and the use of older linear voltage regulators is costing extra money in either less duration or requiring a larger mAH rated battery pack then one might otherwise require. Switching regulators should certainly be the first preferred method considered in this day and age.

For example just using one each of these switching regulators for each servo is a pretty cost effective and certainly more battery efficient way to go:
http://www.ebay.com/itm/251066005460?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Lefty
« Last Edit: December 07, 2012, 01:32:17 pm by retrolefty » Logged

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I've used the below setup for many years to supply servos 5.7v using a 7805 regulator and a small diode.



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Quote
Yes, it looks to be an effective circuit. But keep in mind that when a project is portable and battery based, duration of the batteries is an important and perhaps expensive goal and the use of older linear voltage regulators is costing extra money in either less duration or requiring a larger mAH rated battery pack then one might otherwise require. Switching regulators should certainly be the first preferred method considered in this day and age.

For example just using one each of these switching regulators for each servo is a pretty cost effective and certainly more battery efficient way to go:
http://www.ebay.com/itm/251066005460?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

Lefty

Oh wow, that's nice.  Parts for my circuit from Radioshack were four bucks.  This looks like a much better way to go. 
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Madrid
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thinking about this i found out the LM25118 by TI this will be able to hold a max of 20 amps.


* PowerDistribution.png (41.55 KB, 1301x613 - viewed 7 times.)
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