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HomeAircraftHelicopterHelicopter Main Discussion › Longer Flight Time?
12-08-2017 04:13 PM  10 months agoPost 21
Heli_Splatter

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USA

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gwright... while I don't disagree with you using BECs, I prefer the receiver battery. I have lost an aircraft when the BEC/ESC burned up.

Either method can have failures. Since I will never be on a 3D demo team, I don't mind the extra bit of weight. Tomatoes/tomatos

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12-08-2017 04:58 PM  10 months agoPost 22
gwright

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Champaign Il

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i completely respect that opinion. Many ways to skin a cat, and seperate battery is your preferred method which could easily be argued is more safe and less likely to fail.

BEC is my prefered method with the argument I find it more convenient and it eliminates the risk of me taking off with a dead rx pack.

Gary Wright

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12-08-2017 05:19 PM  10 months agoPost 23
Heli_Splatter

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USA

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well said... could not agree more.

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12-11-2017 10:08 PM  10 months agoPost 24
w8qz

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Grand Rapids, MI - USA

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Theoretically at least, the longest flight time should be with a single-blade rotor head (the blade would fly in relatively smoother air, undisturbed by other blades). It has been done - there' s a video out there. Balancing would take some extra effort, of course.

"The helicopter is much easier to design than the aeroplane, but is worthless when done."

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12-11-2017 11:25 PM  10 months agoPost 25
AirWolfRC

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42½ N, 83½ W

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Hi, Guys, I am building a 700 electric low head speed heli using one 5000ma
battier, what is a better setup for a longer flight time, running all the servos and assures off the main battier or installing a separate flight pack, let say a 2200ma.
What's an "assures" ?

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12-11-2017 11:28 PM  10 months agoPost 26
AirWolfRC

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42½ N, 83½ W

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Theoretically at least, the longest flight time should be with a single-blade rotor head (the blade would fly in relatively smoother air, undisturbed by other blades). It has been done - there' s a video out there. Balancing would take some extra effort, of course.
If you want longer flight times (trading off snappy performance of course) slow down the rotor speed.

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12-12-2017 02:47 PM  10 months agoPost 27
Richardmid1

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Leeds, England

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It depends on the servos, some pull more current than others. The most efficient way would be to run HV servos on 6v or 6v servos on 5v. Generally lower spec servos will draw less current. So for sport flying at low headspeed you don't need 20kg servos with 0.06s transit time! 10kg and 0.1-0.15s transit time will be plenty.

Anyway lets say the overall current draw of the system is 50mA/min. so 500mA in a 10 minute flight (possible on a 700 with single 6s 5000 pack). Using 4000mah (80%), that's 400mA/min. So you would loose over a minute of flight time using the main pack and a BEC to power the electrics!

A 2s 2200mah Li-po weighs around 120g BUT a BEC with all the wires could weigh 50g so your only actually adding around 70g which on a heli weighing around 4.2kg (700 single 6s pack) is only 1.66% extra!

Sooo for flight time, the receiver pack option wins theoretically.

60% of the time, it works every time!

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12-12-2017 03:00 PM  10 months agoPost 28
ICUR1-2

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Ottawa, Ontario

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Does a FBL use more mah than a fly barred?
I think it does but not sure.
If does would a higher gain use more mah ?

spending time, paying attention

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12-12-2017 04:58 PM  10 months agoPost 29
oldfart

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Vancouver, Canada

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Yes, all things being equal (eg. same servos, same blades) an FB system will draw a good deal more power then an FBL system. This is because the fly bar helps move the rotor blades to the desired cyclic pitches.

Digital servos also consume a lot more power then the older analogue servos.

Phil

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12-12-2017 05:28 PM  10 months agoPost 30
AirWolfRC

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42½ N, 83½ W

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Yes, all things being equal (eg. same servos, same blades) an FB system will draw a good deal more power then an FBL system. This is because the fly bar helps move the rotor blades to the desired cyclic pitches.

Digital servos also consume a lot more power then the older analogue servos.
Maybe, maybe not.
On a flybar system, energy comes from the main motor,
On a flybarless system energy comes from the servos.
Either way the energy comes from the main battery.
- - unless you use a separate battery for the servos.

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12-12-2017 06:48 PM  10 months agoPost 31
Flyin for Jesus

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Troy, IL. 62294

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Richardmid1
Anyway lets say the overall current draw of the system is 50mA/min. so 500mA in a 10 minute flight (possible on a 700 with single 6s 5000 pack). Using 4000mah (80%), that's 400mA/min. So you would loose over a minute of flight time using the main pack and a BEC to power the electrics!
A 6s 22.2v pack powering 7.4v servos through a BEC does not consume capacity like you said. 6s in and 2s out is 3-1, so 500mAh out to servos is only 167mAh from the main pack, assuming 100% efficiency.

Also, the 50mA per minute is a 3A constant draw. My 770 drew just over 2A constant doing sport flying.

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12-13-2017 12:56 AM  10 months agoPost 32
ICUR1-2

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Ottawa, Ontario

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Then all were left with is weight...
A trend I noticed the last few years is servo weight has increased significantly.

I searched for full size servos and most are above 56 gram weight most seem to be around 70 grams . It may not seem like allot it does add up.

spending time, paying attention

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12-13-2017 04:07 AM  10 months agoPost 33
gwright

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Champaign Il

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exactly why I use these, at 43 grams
https://www.towerhobbies.com/cgi-bi...?&I=LXDXFG&P=ML

yes, they're marketed as car servos, so I accept responsibility if theres a failure, but I've had them in a 700 and a 600 for a couple years without issue.
my 700 thats in the video I posted is 9 and 3/4 lbs with 12s/4350 packs. It's little things like the lighter servos, very high energy density batteries, BEC instead of separate battery,.. smaller edge 80 esc (60 is fine but need the extra few grams of the 80 for CG)

these servos probably wouldn't be advisable at high rpm with smack style flying but perfect for the way I like to fly.

Gary Wright

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12-13-2017 11:13 AM  10 months agoPost 34
Richardmid1

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Leeds, England

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A 6s 22.2v pack powering 7.4v servos through a BEC does not consume capacity like you said. 6s in and 2s out is 3-1, so 500mAh out to servos is only 167mAh from the main pack, assuming 100% efficiency.
I stand corrected, well spotted.

So in that case then adjusting it to 35mA/min for 10 mins, that's only 117mA from the main pack which means you would only lose around 17.5 seconds.

Sorry for the miscalculations!

60% of the time, it works every time!

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12-13-2017 11:16 AM  10 months agoPost 35
Richardmid1

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Leeds, England

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Yes, all things being equal (eg. same servos, same blades) an FB system will draw a good deal more power then an FBL system. This is because the fly bar helps move the rotor blades to the desired cyclic pitches.
You mean FBL draws more current than FB.

FBL systems also drive the servos at a higher frequency, 200Hz+... I think?!

60% of the time, it works every time!

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12-13-2017 01:07 PM  10 months agoPost 36
ICUR1-2

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Ottawa, Ontario

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Gwright
they're marketed as car servos, so I accept responsibility if theres a failure, but I've had them in a 700 and a 600 for a couple years without issue.

I believe car steering servos are where our current heli servos originate from. From 2003.

spending time, paying attention

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12-13-2017 02:09 PM  10 months agoPost 37
gwright

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Champaign Il

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I think you're correct. low deadband, high torque of course, and fast. hmmm,.. sounds like a heli servo
I started using them primarily due to the weight savings, since they have enough torque and speed. The fact that they're really inexpensive is just a bonus.
I remember in the 80's using "top of the line" servos in large helis (660 and 680mm blades at the time). The 9201's had an amazing 69.5 oz/in torque

Gary Wright

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12-13-2017 02:40 PM  10 months agoPost 38
RM3

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Killeen, Texas - USA

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I remember in the 80's using "top of the line" servos in large helis (660 and 680mm blades at the time). The 9201's had an amazing 69.5 oz/in torque
nowadays you have HV heli servos with enough power to torque the lug nuts on a small car. I think it was a 3D heli pilot (Kyle?) had his cyclics swapped out (by father?) for lower torque units without without his knowledge... the pilot didnt even notice after a few flights.

showing a preference will only get you into trouble, 90% of everything is crap...

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12-13-2017 02:55 PM  10 months agoPost 39
gwright

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Champaign Il

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If I remember correctly, Dave said he set the BEC to 5v instead of 8v on one of Kyle's machines,.. which of course drastically reduces torque and speed of the servos. Very interesting that someone of Kyle's ability couldn't tell the difference.

I think this has strayed way off topic from the "longer flight time" discussion,.. so I'll get back to a relevant post....

Low Headspeed Smooth 3D Rules!

Gary Wright

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12-13-2017 03:32 PM  10 months agoPost 40
ICUR1-2

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Ottawa, Ontario

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In order to achieve longer flying times. You have to consider all the factors. I was merely pointing out that most of today's servos are heavier than when I started this hobby.
As was mentioned earlier we don't really need super high spec servos .

I think I could achieve 10 minutes on a 500 with the proper KV motor and gearing for my sport flying.

spending time, paying attention

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HomeAircraftHelicopterHelicopter Main Discussion › Longer Flight Time?
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