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HomeAircraftHelicopterMain Discussion › Voltage vs Current?
01-03-2014 11:01 PM  4 years agoPost 1
PaulBowen

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Victoria, Australia.

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Hello just a quick question from down under.

It is said that with an electric heli the current requirements will be half if the voltage is doubled. That is one reason I use 12s in my Vibe E8. This is my understanding.

If this is the case then why do they say that a higher voltage through servos will increase the current draw through the system instead of reducing it?

It just seems counter intuitive.

Futaba T18SZ, JR Propo XG14, Hirobo fanatic!

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01-03-2014 11:10 PM  4 years agoPost 2
pip

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Baltimore, MD

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Check out this site for an explanation: http://www.physicsclassroom.com/cla...cuits/u9l3c.cfm

If the resistance (load) stays the same current will increase with the voltage increase

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01-03-2014 11:23 PM  4 years agoPost 3
Andy from Sandy

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If the motor manufacturers made the motors that way then in theory that would be true. If they made the 12S motor have the same power as the 6S motor then it would be true.

If you check out the scorpion website and look at the 4025-1100 and compare it to the 4025-550 you will see the 550 consumes 2850 Watts where as the 1100 it is 2200 Watts. Therefore in this example the current is reduced by 35 Amps and not 50.

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01-03-2014 11:24 PM  4 years agoPost 4
PaulBowen

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So would that suggest I am safer running a regulated 5.0v on my 800 gasser than a straight 8.4v from the LiPo?

Futaba T18SZ, JR Propo XG14, Hirobo fanatic!

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01-03-2014 11:30 PM  4 years agoPost 5
ticedoff8

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Morgan Hill, CA. USA

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All things being the same, if they kept the speed of the servo motor the same as when it was using a lower voltage, then the current it draws would drop with a higher voltage on the servo.

But, they don't keep the motor speed the same.
They use higher voltages to get the servo motor to spin faster. Spinning the motor faster introduces new loads and that draws more current.

But wait, there's more...

Flybarless puts the 3 swash servos under a much higher load than say a flybar'ed head.
So, naturally, FBL servos use more current to provide the power to move the swash.
This is a given for normal voltage servos vs. HF servos.

But, the load on the servo goes up as the speed increase.
Moving a mass (like the swash and the FBL head) increases the load exponentially.
A servo moving a load 10% faster experiences a 40% increase in load.
And a 40% increase in current.

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01-03-2014 11:36 PM  4 years agoPost 6
ticedoff8

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So would that suggest I am safer running a regulated 5.0v on my 800 gasser than a straight 8.4v from the LiPo?
If the servos you have on your 800 gasser are rated at 6v, then you are gambling with a disaster.
You are infinitely safer with a 5v regulator in a setup that uses 6v rated servos and a 2S LiPo.

On the other hand, if you have HV servos, they are designed for 2S LiPo. And you are as safe as you can be - with a heli.

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01-03-2014 11:40 PM  4 years agoPost 7
Andy from Sandy

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Bedfordshire, UK

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So would that suggest I am safer running a regulated 5.0v on my 800 gasser than a straight 8.4v from the LiPo?
This is different to what the OP is wanting to know between 6S and 12S setups. The motors designed for 6S with that 1100Kv typically draws twice the current of a 550Kv motor running on 12S because the wire resistance of the 12S motor is higher and therefor draws less current. This is just simple ohms law.

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01-03-2014 11:40 PM  4 years agoPost 8
PaulBowen

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Victoria, Australia.

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A 5 volt setup is sounding better by the minute for us sport/scale flyers.

Futaba T18SZ, JR Propo XG14, Hirobo fanatic!

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01-04-2014 01:10 AM  4 years agoPost 9
Retired2011

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Lee's Summit, MO

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This is different to what the OP is wanting to know between 6S and 12S setups.
No, he is wanting to know why the higher voltage to servos would increase current draw.
OP
If this is the case then why do they say that a higher voltage through servos will increase the current draw through the system instead of reducing it?
Yes, I have decided to stay at default voltage on my Heli Jive - 5.6v, because the evidence shows an almost impercievable difference with HV servos...even by the pros.

Chet

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01-04-2014 01:48 AM  4 years agoPost 10
PaulBowen

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Victoria, Australia.

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I agree Old Hippie.

My thoughts are that although they are HV servos there is no need to run them under the higher voltages and current.

Kind of like a Ferrari being capable of 300kph doesn't mean it should be driven that fast all day every day

Futaba T18SZ, JR Propo XG14, Hirobo fanatic!

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01-04-2014 01:53 AM  4 years agoPost 11
Retired2011

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Lee's Summit, MO

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There is a thread...I could find it if I had to, but Dave Dahl switched to low servo voltage on one of Kyles helis and didn't tell him. Kyle flew test flights all afternoon and never knew the difference. Another time they found one of his several Logos had been inadvertently switched to low voltage and he flew them all back-to-back for awhile and they couldn't tell any difference.

Edit...here is his post...

Originally Posted by dahld
Thought I'd pass on what I learned today.

I've stated in the past that with the Logo 600, running HV servos was unnecessary. I said this because I once pulled a fast one on Kyle, and lowered the BEC voltage on one of his Logo 600's before a practice session, and didn't tell him. After flying all afternoon, he couldn't tell the difference in how the heli with the lower voltage flew, compared to the helis with the higher voltage.

So we've been running the Logo XXtreme with HV servos on 8.4V, via a Western Robotics 14S 10amp BEC. But with the YGE ESC we've been running, in order to use its programming card, you have to lower the system voltage to 5.2 volts or lower (the card won't work for some reason at the higher voltages???), which we can do with the WR BEC, as it has several programmable voltages accomplished via micro dip switches on the unit. When done with the programming card, we bump the voltage back-up to 8.4V

So today, while doing some adjusting on the V-Bar via the laptop, I noticed the V-Bar was reading the system voltage at 5.2 volts. When I checked the BEC, sure enough, the dip switches were set for 5.2 volts.

The last time I used the YGE's programming card on the machine in question, was probably 30+ flights ago. So all this time, Kyle's been flying one XXtreme at 8.4V, and the other at 5.2 volts (using JR 8717HV servos), flying and practicing aggressive XFC competition type routines with both machines, and couldn't perceive a difference in how they flew.

So, when you get an XXtreme, use what you want, standard or HV, looks like it doesn't really matter.

That said, don't skimp on the system's power supply. Until there's data to prove otherwise, I'm still thinking a 10 amp capability is the safe bet.

(-: Dave

Chet

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01-04-2014 02:14 AM  4 years agoPost 12
PaulBowen

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Victoria, Australia.

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Fantastic post Old Hippie!

Thats answered many of my questions.

Futaba T18SZ, JR Propo XG14, Hirobo fanatic!

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01-04-2014 08:47 AM  4 years agoPost 13
Andy from Sandy

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Bedfordshire, UK

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@old hippie

Thank you. Yes I read the OP wrong, sorry about that.

If everything about a circuit stays the same then as the voltage is increased there will be a higher current flow. And it is still all about ohms law.

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01-04-2014 01:12 PM  4 years agoPost 14
Retired2011

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Lee's Summit, MO

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Here is a very simple way to see it in action...
http://phet.colorado.edu/en/simulation/ohms-law

Chet

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01-04-2014 02:59 PM  4 years agoPost 15
dcasole

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Dacula GA

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Thanks hippie ...that puts a lot of "urban legend" to bed

Dave

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01-04-2014 08:13 PM  4 years agoPost 16
icanfly

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ontario

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it's good timing you ran this topic. I'm about to run my rebuilt and fbl converted nitro Shuttle zx and have analogue JR 507's, which are 6v max. I have a CC 10amp bec. The system runs a Spektrum AR 6200 with satellite, a GWS gyro in line to the pitch and roll servos while the tail has an Align GP 780 digital gyro. If you see my fbl conversion using original cranks the resolution and load should be no worse than with the fb, actually less because the servos are not fighting mechanical resistance from the flybar.

My battery is a Flight Power 30c 2200mah 7.4v lipo which I can double up amof to increase my outing time (no need to recharge all day). I don't know how much the entire assembly will draw but owe it to the machine and myself to do the math before it goes airborne. I want to be certain the switch from nicad to lipo is in order and how many ma hours/minutes the lipo will last before dropping below 4v and needing recharging. I do have a low voltage alarm for it also.

this pic should give you an idea,

everything will probably be fixed in the next coming days when my self made mounting trays are attached. Battery might be shifted forward at the very front of everything to provide better balance, a cf tail tube is being sought atm.

A upgrade to zxx starter and clutch assembly is a future consideration as it will cut weight by 100grams. What is being learned on this baby will be in preparation for anything to come. Why did the guy climb Mount Everest? Because it was there.

an off the top estimate of a 1000mah system would last 4 hrs consuming half of the 2200mah lipo roughly 8v max capacity.

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01-04-2014 08:55 PM  4 years agoPost 17
dcasole

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Dacula GA

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Ur estimate us way conservitive ..u do not not need to worry about your shuttle
I fly the crap out of my shuttle that has much bigger servos than your JR's and the max I take out per flight is 200 mah
So because I am conservitive also I charge after 4 flights
Just fly it a few times, measure what you put back in and eventually you will know how many flights you can safely do before charging

Also you don't want to run that lipo ( or nicad pack for that matter) down to 4 volts

3.8 per cell is the farthest I would run a lipo down
Good luck with the shuttle

Dave

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01-04-2014 09:28 PM  4 years agoPost 18
icanfly

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ontario

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thanks for that, your 200mah per (10 to 15min) flight should be about 1000mah.

The Shuttle is interesting because it was pre cf and post prehistoric so it has most of today's mechanics but not as pretty. A few things on it are junky and they were in the learning curve of what became the zxx top start (I plan to upgrade to)

Sometimes too much high tech can be dizzying and costly, not much in the way of improvements to a Shuttle can be made other than aluminum/cf and smaller lighter electronic support. The core is all the same.

Now my 450s look like kids stuff.

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01-04-2014 11:14 PM  4 years agoPost 19
PaulBowen

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Victoria, Australia.

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I think this is a good subject for discussion as it is not easy to find info on what is and isn't appropriate in terms of power supply. I have found some suppliers (and manufacturers) can also be a little vague at times.

I am not someone that has a lot of crashes. This is part luck and part my conservative flying style. Unfortunately I have recently crashed a brand new very expensive gassers (on its 10th 20 minute flight) due to an apparent equipment failure. This creates a hell of a lot of self doubt and erosion of confidence.

I think it would be good to have a reference showing different levels of acceptable power system for different flying styles, servos, gyros and heli sizes. This would be a great guide when setting up a new model.

Futaba T18SZ, JR Propo XG14, Hirobo fanatic!

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01-06-2014 04:05 PM  4 years agoPost 20
bagobitz

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saddleworth,lancs,UK

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A bit of generalisation, for what it's worth.

Voltage is good! a low voltage rail wil be more suceptible to volts and current-drop through joints....It's inevitable that any push-connector will have a considerably smaller cross-section than the conductors going to-and from it.

In an ideal world, you'd have servos, receivers, Gyros and motors rated at the max. voltage of your on-board power-supply...The reality is that you have to drop and stabilise the available battery-voltage ,to suit the various devices.

IMO, a bit of time and money spent on heavier-gauge wiring (TINNED copper!) and better-quality connectors, will repay , with reliability, less voltage drop andtherefore optimum output.
As explained elsewhere, If you increase the voltage, you increase the current and power UNLESS you also increase the "resistance" to keep the power the same, in which case, you reduce the current, so the wiring doesn't heat up and the voltage doesn't drop..

Obviously, that's a bit simplisticbut the bones are there!

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HomeAircraftHelicopterMain Discussion › Voltage vs Current?
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