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HV servos with stock RX??

Old 07-30-2013, 08:03 AM
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daveopam
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Default HV servos with stock RX??

Was thinking about trying some high voltage Hitec servos and a 2 cell Lipo without a reg. I use Futaba 2.4 7ch RX's and nowhere does it say if they will handle the 7.4V the 2S lipo will put out.
Surely I am over thinking this and they will handle the voltage. I just dont want to fry a $80 RX to find out.

Any help is welcome and thanks, David
Old 07-30-2013, 08:53 AM
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Default RE: HV servos with stock RX??

I've been asking this same question and have been getting different answers. The Rx I use is the 617FS and the specs say it's rated for 4.8v - 6v. Some guys are saying that they run 7.4v with no reg and have no problems. Futaba says to use a reg and if you want to use 7.4 and HV servos buy a HV Rx.. That's what I was told.
Old 07-30-2013, 09:45 AM
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Default RE: HV servos with stock RX??

Any Rx that does not state HV is rated up to 8amp. Most Hv, digital, and even high speed servos combined (2 or more moving simultaneously) will over load the Rx. Not to say it can not be done, for example a servo rated a lets say 200oz will not pull full amps if  the linkage is set up on the short side of the servo and the long side of the control surface. Hook the servo up at 1-1/4 and the control horn at 1/2 and one will most certainly short the servo. Servos are rated at the 1" linkage mount hole (with exception to a couple, savox being one),  go 3/4 and the torque is reduced by 25% thus reducing the load and amps. These are the reasons many well experienced pilots speak so much of set-up.
Old 07-30-2013, 01:55 PM
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Default RE: HV servos with stock RX??

I did not realize there were HV RXs. It makes sense that there would be now that I think about it. I wonder what the money difference is? I don't see an advantage if it's more than the $50 a good reg can be had for. The servos are slightly quicker and stronger on 7.4v compared to 6.0v but it's not night and day.

David
Old 07-30-2013, 02:24 PM
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Default RE: HV servos with stock RX??

Here's a Futaba HV Rx www3.towerhobbies.com/cgi-bin/wti0001p quite a bit more money.
Old 07-30-2013, 04:33 PM
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Default RE: HV servos with stock RX??



I don't spend the extra for HV, but will for the HS occassionally. I set up appropriately and test the current before the build is finished. As I said above the current can be diminished by the load being applied and the load being applied can be diminished by the linkage set-up. And if the airframe is large enough to require the HV, digital, HS servos then I will use a power panel to funnel the load current through instead of the RX. One can be made easily or purchased reasonably.

Old 07-30-2013, 04:55 PM
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Default RE: HV servos with stock RX??

One other note, in any system the servo power (red and black wire) does not have to be run through the Rx, they can be redirected directly to a power source. Only the white wire absolutely has to run through the Rx. Thus eliminating any load on the Rx.
Old 07-30-2013, 04:58 PM
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Default RE: HV servos with stock RX??

Thanks for the info.
Old 07-30-2013, 10:42 PM
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Default RE: HV servos with stock RX??

Hello,
I too use the Futaba R617FS. I am going to be building a .40 size plane with digital servos. Probably more an exercise on how to do it but I was going so I can scale it up for larger planes. I am planning on a life for the Rx with only the white wire from the servos goin to the Rx. The white and red wires from the servos will go to a seperate larger life. This is purely to eliminate the current going through the Rx.

Basically white servo wires from each servo going to a corresponding Rx channel. Connect all the black servo wires to the neg terminal and all the red terminal wires to the positive?

I havent even tried this so it's a bit cheeky asking for advise but is it as simple as that?!

Thanks
Old 07-30-2013, 10:49 PM
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Default RE: HV servos with stock RX??


ORIGINAL: Goldenduff

Hello,
I too use the Futaba R617FS. I am going to be building a .40 size plane with digital servos. Probably more an exercise on how to do it but I was going so I can scale it up for larger planes. I am planning on a life for the Rx with only the white wire from the servos goin to the Rx. The white and red wires from the servos will go to a seperate larger life. This is purely to eliminate the current going through the Rx.

Basically white servo wires from each servo going to a corresponding Rx channel. Connect all the black servo wires to the neg terminal and all the red terminal wires to the positive?

I havent even tried this so it's a bit cheeky asking for advise but is it as simple as that?!

Thanks
I'm sure the experts can tell you but I'm putting money on it not being as simple as that...

Old 07-30-2013, 11:00 PM
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Default RE: HV servos with stock RX??


ORIGINAL: Goldenduff

Hello,
I too use the Futaba R617FS. I am going to be building a .40 size plane with digital servos. Probably more an exercise on how to do it but I was going so I can scale it up for larger planes. I am planning on a life for the Rx with only the white wire from the servos goin to the Rx. The white and red wires from the servos will go to a seperate larger life. This is purely to eliminate the current going through the Rx.

Basically white servo wires from each servo going to a corresponding Rx channel. Connect all the black servo wires to the neg terminal and all the red terminal wires to the positive?

I havent even tried this so it's a bit cheeky asking for advise but is it as simple as that?!

Thanks
Found this.. it shows how to achieve what you want.

You must have the Black and white wires still going into the RX...

http://www.gibbsguides.com/article06...wer-supply.htm



Old 07-31-2013, 07:55 AM
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Default RE: HV servos with stock RX??

I also looked on Tower. the HV RXs are all sbus type. For what I was wanting to do it just does not seam like it is worth it to go through sepperating servo wires or regulating just the RX. I do thank everyone for the input. The electronic part of this sport/hobby is the hard part for me.


David
Old 07-31-2013, 08:09 AM
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Default RE: HV servos with stock RX??

The Rx that I posted gives you the option to use 8 inputs or sbus. I'm with you, the electronic part is not my cup of tea..lol
Old 07-31-2013, 09:14 AM
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Default RE: HV servos with stock RX??

Yes it is as simple as that. Use a Y off of the battery if the battery does not have dual leads. One to the Rx battery port and the other to the servos red and black. Absolutely no load through the Rx with this method. Leaving the black wire as in GibbsGuides as posted does leave a path for loading the Rx.
Old 07-31-2013, 09:16 AM
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Default RE: HV servos with stock RX??

I would also like to add that "Yes" it does seem like a bit. But after the first time you will see there is nothing to it, very simple.
Old 07-31-2013, 09:41 AM
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Default RE: HV servos with stock RX??

And if you want an easy way, go down to Radio Shack (or similar) and buy two terminal block's, one for + and one for - with enough spaces for the servo wire and supply. One like shown in the photo will support five servos and the lead.
Old 07-31-2013, 12:11 PM
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Default RE: HV servos with stock RX??

Thanks for the intel Robert & drube. I did not realize the S Bus RX could be used as a normal RX. If I needed an 8 channel RX it might be worth trying the HV. As it is I just cant see good cause to get away from a good reg and normal servos. I would tinker further if this was a 150cc plane. As it is this is a 30cc plane. Room is tight in places and I am really anal about saving weight.

Thanks again, David
Old 07-31-2013, 12:22 PM
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Default RE: HV servos with stock RX??

Dave I do as you speak of. Most of my airframes are basic, standard stuff. But there is always the occasion for a bit more, such as my current 46% Pitts build. I had to step it up a little more than usual for that size. But even some of the smaller airframes have gotten the servo separation from the Rx, that just makes good sense. Example; take 4-6 Futaba 3010's moving around at the same time and the voltage gets quite high.
Old 07-31-2013, 01:37 PM
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Default RE: HV servos with stock RX??

I am sure you are right Robert. It's just not an area I am real comfortable with. My original idea was to build this 30cc Ultimate with a good 2S lipo running the ignition and servos without the use of a regulator. The new DLE ignitions will handle the voltage so I thought if the RX would also take it I could run the whole plane on HV from one battery and make things simple and light. I could still do it, but it's turning into more than I bargained for. Maybe I can study up and try it on a future project.
Would love to see a picture of your 46% Pitts. Does it compare in size to the H9 46% Ultimate? I was shocked at how small a full scale Pitts was the first time I walked up on one.

David
Old 07-31-2013, 01:39 PM
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Default RE: HV servos with stock RX??

High voltage servos, digital servos, and electric retracts all represent challenges to the classic receiver installation and power source.
High peak currents and/or higher applied voltage are obviously the culprit.
My personal experience with this sort of thing involved several seemingly unexplained occurrences of temporary control loss,
intermittent retract gear operation, and so forth.

When all was said and done - - -
One digital servo had an odd failure mode, causing excessive (1.5A) current draw when the servo moved in one direction.
A fairly popular 60A ESC with a built-in BEC was found to have poor peak current capability. The BEC was rated for up to six or so servos,
and 2A+ continuous current.
More than one example of a popular 60-120 electric retract was found to have higher peak current draw than rated or anticipated. A more recently received example of the same electric retract has slower operation and reduced current, and seems to meet the listed current specs. Even so, the retract mechanisms can occasionally get out of sync and require an additional cycle or so to re-sync, using a 6V 6A BEC.

As a result, when I plan on using electric retracts, A separate BEC is used to provide power. The positive power lead is disconnected from the receiver connector, the negative lead from the BEC is in common, and the plus lead fed from the BEC. Since my models are electric powered, The BECs are fed from the same Lipo providing power to the motor speed control.

A newer model 90A speed control from Castle (Talon) has a high current BEC built in, and may be able to eliminate the need for a second BEC in my applications.       
Old 07-31-2013, 02:13 PM
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Default RE: HV servos with stock RX??


ORIGINAL: acerc

AnyRx that does not state HV is rated up to 8amp. Most Hv, digital, and even high speed servos combined (2 or more moving simultaneously) will over load the Rx.
Ok, i'm kinda worried about my set up choices after re-reading this... When it comes to voltage and amps, I get confused. I could never be an electrician. lol

I'll be using 1 Fromeco Lithium Ion 2600 mAh batt with a Reedy 6v 5A reg www3.towerhobbies.com/cgi-bin/wti0001p and 6 Savox 1258TG digital servos www.savoxusa.com/Savox_SC1258TG_Digital_Servo_p/savsc1258tg.htm with my R617FS Rx. I'll be using a seperate batt for the ignition.

Will this work? Am I in any danger of buring up a servo or my Rx?



Old 07-31-2013, 04:39 PM
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Default RE: HV servos with stock RX??

drube if you would click on the technical info for that servo it states at stall it will pull 5amp. Now you put two of those into a heavy load and you are reaching 10 amp, now add one more and you have exceeded most standard Rx's load capability. I am not saying it will not work, many people do it without a thought. I am just saying I see many issues in my club where it is a simple overload taking place. The overload does not have to be enough to short or shut the Rx down but it can and often will create other issues. Issues such as buzzing servos, eratic surface movement, accelerated battery consumption, momentary loss of signal. Like I said above, that little gadget from Radio Shack, 2 of them is ten buck's, and there will never be an issue. I personally like taking to the air with the best odds of a safe return.
Old 07-31-2013, 04:43 PM
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Default RE: HV servos with stock RX??

Think about a banking turn. There are two servos minimum for ailerons, one minimum for elevator, one minimum for rudder, and the throttle all in play at one time. Even if they were using half there rated amps for this maneuver with 5 servos X 2.5 amp =10 amp load. Kinda pushing the envelope for me.
Old 07-31-2013, 04:57 PM
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Default RE: HV servos with stock RX??

Wow. So really I would be better off with a 6v 10A reg if I chose to go that route? Can you recommend a regulator?
Old 07-31-2013, 05:15 PM
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Default RE: HV servos with stock RX??

Check out this place https://www.smart-fly.com/index.html I use a lot of there stuff. But that does not negate the issue of excessive amps. The regulator would just not give any more power than rated (10 amp) even if 12 was needed. The only true method of insuring supply of needed amps is separating from/bypassing the Rx. Most use a power panel to do such and I have as well but those terminal blocks work just as well.

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