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Old Feb 22, 2012, 07:46 AM
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scruffy1's Avatar
Australia, NSW, Fairlight
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Help!
using a 2s lipo direct to the rx

here's the deal :

i am building a binary 900, and would ideally like to simply plug a 2s lipo into the rx and run the 3 servos involved without causing them to fry

is this possible without some other electronics to step the voltage down to the 6v the servo specs list as tolerable ?

for the record, the equipment is :

orange rx r610 which states in their data "Input voltage: 3.7~9.6V"

arrow servos which allegedly manage 6v

now, if i directly attach a 2s lipo - in this instance the Turnigy nano-tech 180mAh 2S 25C Lipo Pack - do i have a great thing happening ?

or do i briefly witness the intoxicating spectacle of the magic smoke being liberated from the servos ? or the receiver ? or all of the above ?

i am after the lightest appropriate ~200mah pack for my dlg, and this might be a winner if death of components isn't likely

let the erudite input begin, and release me from my ignorance, because i'm itching for this to be possible

thanks in anticipation of educating me
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Old Feb 22, 2012, 08:12 AM
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Three diodes in series should provide about a 2.1 volt drop from 7.4 to 5.3 without impeding current flow unduly. Rectifier types rated for 2-3 amps should be more than enough.
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Old Feb 22, 2012, 08:18 AM
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Quote:
Originally Posted by whitecrest View Post
Three diodes in series should provide about a 2.1 volt drop from 7.4 to 5.3 without impeding current flow unduly. Rectifier types rated for 2-3 amps should be more than enough.
i'm sure that's an answer, but for my abilities with electronics it may just as well have been in swahili

one more time if you would indulge me, but this time as if you were trying to explain it to an idiot (that's me dealing with circuit details, for the record)
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Old Feb 22, 2012, 08:45 AM
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Here's a better explanation:
http://www.allaboutcircuits.com/vol_3/chpt_3/1.html

Basically, you want to run the battery's current through 3 diodes before it gets to the receiver which will also power the servos. The diodes must be oriented correctly (forward biased) or the current will not flow. As the current flows through each one, the voltage will drop about .7 volts (for silicon rectifiers). You can use more or less rectifiers to get just the right amount of voltage drop. They can be obtained from Radio Shack and similar stores very inexpensively.
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Old Feb 22, 2012, 10:58 AM
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Canada
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ermm... buy and fit a bec gizmo, yes it may weigh 3 or 4 grams, so what ?
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Old Feb 22, 2012, 12:00 PM
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Doug Bartley's Avatar
Canada, ON, Owen Sound
Joined Oct 2008
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Remember a 2S lipo fully charged is 8.4 volts! 6 volt servos willl quickly be destroyed at this level. Hk has tiny Becs available in 2-3A, tied to a small 2S lipo, I hardly think the weight (4 gr) would affect your plane.
The other option of course is to use the Bec already in most Esc's of this size. I run all my smaller planes (3S) on the 2-3A bec built in, never had an issue. FWIW Doug B
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Old Feb 22, 2012, 12:07 PM
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Lnagel's Avatar
Moab, Utah, USA
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Quote:
Originally Posted by scruffy1 View Post
here's the deal :

i am building a binary 900, and would ideally like to simply plug a 2s lipo into the rx and run the 3 servos involved without causing them to fry

is this possible without some other electronics to step the voltage down to the 6v the servo specs list as tolerable ?
No, it is not possible. You will have to use some type of electronic device, be it diodes, a regulator or a BEC, to step your voltage down to an acceptable level. Do some research and heed the advice of those who have already posted.

Larry
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Old Feb 22, 2012, 05:13 PM
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many thanks to all the above replies

as to the weight of 2-3 grams not being an issue : this may be true in most planes, but dlg benefits from minimal baggage, and then there's the difficulty in finding a space in the fuselage pod to fit anything bigger than (say) my knowledge of circuitry



and so, the research continues...
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Old Feb 22, 2012, 05:24 PM
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Quote:
Originally Posted by whitecrest View Post
Here's a better explanation:
http://www.allaboutcircuits.com/vol_3/chpt_3/1.html

Basically, you want to run the battery's current through 3 diodes before it gets to the receiver which will also power the servos. The diodes must be oriented correctly (forward biased) or the current will not flow. As the current flows through each one, the voltage will drop about .7 volts (for silicon rectifiers). You can use more or less rectifiers to get just the right amount of voltage drop. They can be obtained from Radio Shack and similar stores very inexpensively.
thanks for your assistance - i am still way below the threshold for enlightenment in electrics, having only recently moved on from 2 channel 29mhz thermal gliders after probably 30 years of experience

my building skills are pretty good, but as my expertise has risen, so has my visual acuity fallen, and apart from understanding a new (to me) field of the hobby, i can't solder well, although i do possess a low power variable soldering station which i plan to improve my abilities using

given the prices at hobbyking mailed here (to australia) it is way easier to buy rather than manufacture electronics - the same for planes really, but i am an avid scratch builder, so that balances the price versus spare time and satisfaction of diy

thanks again to all contributors
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Old Feb 23, 2012, 01:57 AM
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Unfortunately NQRC has just stopped trading, but this is the sort of product specifically for what you want. The 5-6g you gain on the regulator is more than made up by the reduced weight of a 2S LiPo.

Here's an option that is available Dimension Parkbec , dirt cheap shipping. I use in power models, but can't see why not for a DLG.
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Last edited by scirocco; Feb 23, 2012 at 03:25 AM. Reason: fix bad link
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Old Feb 23, 2012, 02:07 AM
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thanks for that info - the link is 404 unfortunately

however, my research leads me in other directions, and i thus cut and paste this from my build thread :


well, the options are now hotting up, as instead of a 2s battery and bec stepping it down, i am possibly more inclined to a 1s pack and stepping it up

especially when there's :

600mah 1s battery


ZIPPY 600mAh 20C single cell
Dimensions: 50x30x5mm
Weight : 14.8g

and a booster for 6v

Lipoly Single cell voltage booster for Receivers
This little unit plugs into your single cell lipoly and will boost the voltage to 5V, allowing you to run a receiver on a single cell lipo!
Why would you want to do this? Less weight of course!

Operating Voltage : 2.7V - 4.2V
Operating Current : 1A
Max operating Current : 1.5A
weight on the reviews is 4.4 gm

admittedly the battery needs a plug attached, but let's face it, 600mah for under $7 at a weight of 19.2gm plus a plug is a major bonus if i can get the cg in the right spot with what i have lined up

that's now ~125gm all up except for the aileron rods and some glue

wooties !


additional : post to oz is $5.99 i think
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