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Old Jan 27, 2013, 04:50 PM
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United States, IL, Lombard
Joined May 2009
3,344 Posts
Actually, I'm glad I built this Swift 16 for another reason - it restored my faith in heli-math !

On my Swift NX I calculated my head speed should have been around 1650 RPM given the following:
  • 1100kV motor
  • 9T pinion
  • 6S Lipo
  • 80%-ish throttle curves
  • Electron 80/100A Century ESC
Well, it wasn't. Instead I got 2000-2100 RPM on the maiden flights. Still do. (?)

But, on my newly built Swift 16, I also calculated a head speed in the 1600 RPM range given the following:
  • 800kV motor
  • 12T pinion
  • 6S Lipo
  • 80%-ish throttle curves
  • YEP 100A ESC
And that RPM range is exactly what I got on the maiden flight. Good - the math works! I'm using the same battery and Tx too (DX6i).

What that tells me is on the NX either the Century ESC isn't functioning as expected or the 1100kV motor is actually a mis-marked 1300kV motor. I'm hoping it's the ESC so I can justify replacing it with a YEP 100A. The 5A/6A BEC on the YEP will then allow me to shed some weight - 8A regulator, 2S lipo, metal bottom plate, extra wires & connectors.

I can swap motors around now that I have another platform to verify - but first I must re-solder bullets and sockets on the 1100kV and 80/100A. The previous owner put the bullets on the ESC and sockets on the motor
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Old Jan 27, 2013, 07:00 PM
Registered User
Utah
Joined Sep 2009
499 Posts
I don't know why more people don't use 2 3s batteries instead of a (usually), more expensive 6s.

My first 550 was a Gaui, and it uses 2, 3S batteries; one on top and one slung underneath. The benefits are: 2, 3s batteries are usually cheaper than a 6s; and if you fly 450 helis you probably have a bunch of 3s' already!

It's too bad the RTF is such a piece of junk... I have an unflown one I was going to sell along with a lot of my other stuff! I have some major med bills coming and will be drastically thinning my rc fleet

ciao
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Old Jan 27, 2013, 07:23 PM
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United States, IL, Lombard
Joined May 2009
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Swift 16 with two 3S 2200mAh 35C Lipos in Series ?

I guess it would depend on their capacity - mine are only 2200's, so all other things equal I would expect 2200/3300 = 67% of the flight time I had before, which works out to like 3.3 minutes (5min * .67). But that's running 2100 RPMs and flying pretty darn fast with big loops and fast banked turns (which sucks a lot more current). Dropping the RPMs to 1500-1600 and flying more scale-like should increase that 3.3 minutes, but to what is the question. (Answer: 6.7 minutes - see EDIT below)

I was looking at 3S 3300 packs and they're they same length & width, half the height, half the price (of a 6S 3300), but a little heavier when two are used. But, there is now the opportunity of better/alternate placement, which could be worth the extra weight.

Another small benefit - two 3S 2200s only weigh 384g, while my 6S 3300s weigh 513g and 560g. So there is a 129g - 176g reduction in all up weight with two 3S packs ... not much (5-6%), but a little bit back in the right direction.

EDIT: (Encouraging read.) If accurate, this is the exact information I need ... http://www.leisuretech.ca/index.php/...ery-for-swift/

The author indicates some interesting power requirements for given head speeds:
  • 1500-1600 RPM - 400 to 470 Watts
  • 1600-1800 RPM - 470 to 600 Watts
  • 1800-2100 RPM - 600 to 800 Watts, with 1275 peaks
So I'm running 2100 RPM (800W) now, getting 5 minute flights, and want to drop it to 1500 (400W). Doing so should cut the power requirement by half, so I would expect twice the flight time, or 10 minutes (with my 6S 3300 pack). Now if I drop down to a 6S 2200 pack (two 3S 2200 packs, 67% of 3300) I should be at 6.7 minutes, so a 5 minute flight with my two 3S 2200s might actually be possible. (Which is probably all the RTF Swift can honestly achieve with an 8T or 9T pinion, depending on the motor 1440/1300).

A 75% throttle curve should get me close to 1500 RPM. I'll switch to my Edge 523mm CF blades as well - they'll reduce the amount of current required to fly compared to the woodies (less drag). My CG is going to be off (tail heavy) so some forward trim may be required - as long as I don't try any inverted flying that should be okay.

Gotta build a series y-cable now and try it .... (apologies - typing this stuff out helps me keep things straight)
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Old Jan 28, 2013, 02:45 PM
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Quote:
Originally Posted by FR4-Pilot View Post
.......
  • 1500-1600 RPM - 400 to 470 Watts
  • 1600-1800 RPM - 470 to 600 Watts
  • 1800-2100 RPM - 600 to 800 Watts, with 1275 peaks
Those are pretty well right on. What you may not know is that they are all relative to an ESC that is set in the non-governor mode, using proper gearing and KV motors, to get the rotor speeds using a flat 100% throttle curve. In other words, where the ESC is working at its top efficiency.

Once you start using settings at less then 100% and/or in governor mode of most ESCs, you will be bringing in some inefficiencies. So you may find that if you need 800 watts at a 2100 rpm, it may not correlate exactly to 400 watts at 1500. But with a good ESC, it should not be too different.
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Old Jan 28, 2013, 09:48 PM
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United States, IL, Lombard
Joined May 2009
3,344 Posts
Swift 16 with two 3S 2200mAh 35C Lipos in Series (con't)

That's good to know - thanks! I have a plan A and B.

Plan A involves leaving the 12T pinion on and reducing the throttle curve to 75%, which should put the RPMs around 1500. I want to see how well the YEP/YGE active freewheeling handles the less than 100% throttle curve. If this ESC works as well as claimed then the following approximate head speeds should be possible by just varying the throttle curve:
  • 2000 RPM - 100% Throttle
  • 1900 RPM - 95% Throttle
  • 1800 RPM - 90% Throttle
  • 1700 RPM - 85% Throttle
  • 1600 RPM - 80% Throttle
  • 1500 RPM - 75% Throttle
That's a pretty good range ! I should be able to find one or two that I like

Plan B involves changing to a 9T pinion and running with 100% throttle curves. This should also put the RPMs around 1500.

Some more calcs put the hovering current draw at around 18A. Those 35C packs should be good for 77A.

Got the series Y-adapter built tonight Just in time for some winter thunderstorms tomorrow - and 60F !!?!!
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Old Feb 02, 2013, 10:12 AM
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675 Posts
FYI. If you plan to use a bec, make absolutely sure that the negative is tied to the negative side of the main connector and NOT the negative between the two flight packs or you will have a floating ground condition.
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Old Feb 03, 2013, 03:04 PM
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United States, IL, Lombard
Joined May 2009
3,344 Posts
Swift 16 with two 3S 2200mAh 35C Lipos in Series (con't)

Good advice on the BEC - thanks. I'm using the internal 5A/5.5V BEC on the YEP for now.

A 4 minute test flight with two 3S 2200 35C packs wired in series. 75% flat throttle curve. Standard 0-50-100 pitch curve. RPMs started out around 1510 and ended at around 1370 (followed voltage drop) - extra blade pitch (& drag) required to compensate. Flew okay, but I think I can improve things with different throttle & pitch curves. Batteries, ESC and motor all came down barely warm. Managed to get 4 mins out of this setup. All cells around 3.83V after flight. (Need to see how many mAhs were used). Next will try blades with less drag (Edge 523 CFs), less steep pitch curve, a slightly sloped (up) throttle curve and see if overall flight response & flight time improve. No governor.

Century Swift 16 - Flight #2 - 1500 RPM (4 min 42 sec)


UPDATE: I just recharged the packs from flight #2 (in series, as a 6S pack) and put 1180mAh back in. This is great news! This means the average current draw was around 17.34A (289 mAh/min) and results in an estimated flight time of 6 minutes 5 seconds ! Going backwards it looks like it took around 385 Watts for Flight #2. I'd say a 5 minute flight is within reach !!! Some easy going forward circuits will help use even less power than just hovering once translational lift kicks in

Flight #2 was approximately 4 minutes & 5 seconds = .06805555 h

1.18Ah / .0680555h = 17.339A (Average current draw from batteries).

17.339A * 22.2V = 384.926 Watts (Required to fly the heli)

This results in a projected flight time of

1.760 Ah / 17.339A = 6.09 minute flight = 6 minutes 5 seconds (leaving 20% in pack)
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Old Feb 03, 2013, 04:54 PM
Beginner Pilot
United States, NY, Coram
Joined Jul 2012
374 Posts
I have a Swift Nx airframe and a TON of parts that I no longer have use for. If anyone is interested and wants more info. Send me a pm.
Thanks

Jeff
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Old Feb 03, 2013, 05:30 PM
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Power Up's Avatar
Northern Ontario
Joined Mar 2007
1,571 Posts
Hey John! It looked & sounded great. The low RPMs certainly give it a whuup/whuup kind of sound. Nice canopy! The white stuff makes it look a little more like my neck of the woods .
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Old Feb 04, 2013, 05:53 AM
Beginner Pilot
United States, NY, Coram
Joined Jul 2012
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Swift Nx for sale!!!!! http://www.rcgroups.com/forums/showt...4#post24028620
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Old Feb 05, 2013, 06:13 AM
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http://www.rcgroups.com/forums/showthread.php?t=1824434
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Old Feb 05, 2013, 07:22 AM
WOS
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United States, IN, Michigan City
Joined Nov 2003
808 Posts
Quote:
Originally Posted by FR4-Pilot View Post
Good advice on the BEC - thanks. I'm using the internal 5A/5.5V BEC on the YEP for now.

A 4 minute test flight with two 3S 2200 35C packs wired in series. 75% flat throttle curve. Standard 0-50-100 pitch curve. RPMs started out around 1510 and ended at around 1370 (followed voltage drop) - extra blade pitch (& drag) required to compensate. Flew okay, but I think I can improve things with different throttle & pitch curves. Batteries, ESC and motor all came down barely warm. Managed to get 4 mins out of this setup. All cells around 3.83V after flight. (Need to see how many mAhs were used). Next will try blades with less drag (Edge 523 CFs), less steep pitch curve, a slightly sloped (up) throttle curve and see if overall flight response & flight time improve. No governor.

http://www.youtube.com/watch?v=avk3IIIVpnE

EDIT: I just recharged the packs from flight #2 (in series, as a 6S pack) and put 1180mAh back in. This is great news! This means the average current draw was around 17.34A (289 mAh/min) and results in an estimated flight time of 6 minutes 5 seconds ! Going backwards it looks like it took around 385 Watts for Flight #2. I'd say a 5 minute flight is within reach !!! Some easy going forward circuits will help use even less power than just hovering once translational lift kicks in

Flight #2 was approximately 4 minutes & 5 seconds = .06805555 h

1.18Ah / .0680555h = 17.339A (Average current draw from batteries).

17.339A * 22.2V = 384.926 Watts (Required to fly the heli)

This results in a projected flight time of

1.760 Ah / 17.339A = 6.09 minute flight = 6 minutes 5 seconds (leaving 20% in pack)
WHat software or tool are you using for the graphs?
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Old Feb 05, 2013, 10:48 PM
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United States, IL, Lombard
Joined May 2009
3,344 Posts
Quote:
Originally Posted by WOS View Post
WHat software or tool are you using for the graphs?
For the throttle and pitch curves I'm using "Hobby Central" (?).

For the audio head speed analysis I'm using "Heli-Headspeed" and "Audacity".

Also using "Head Speed Calculator (v1.0.10) too.

And Microsoft Paint to draw/add text on the graphs.
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Old Feb 06, 2013, 01:42 AM
If I build it, it will fly
United States, NY, East Rochester
Joined Jan 2012
699 Posts
Time to ask a big secret. What pitch curve goes with what headspeed?

~psguardian
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Old Feb 06, 2013, 01:37 PM
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Georgia, USA
Joined Jan 2008
3,761 Posts
My favorite kind of flying. With the Heli Jive ESC I can just turn down the throttle curve
Just wish I could fly a fraction as good as Sebastian

Head speed here is 1100-1200 SMOOOOOOOOTH


10 Minutes Low RPM flying with the 7HV (10 min 7 sec)
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