4 cell H-quad build (aka Matt doesn't like eCalc results)

[Matt_mg]

Hi guys, I've flown a few blade helis and quads but now I want to build my own H with a flite test frame.

I've been reading around the web for a few configurations and I wanted to try something like this:
http://ecalc.ch/xcoptercalc.htm?ecalc&lang=en&cooling=2.5&rotornumber=4&weight=225&calc=sum&elevation=500&airtemp=25&qnh=1013&batteries=lipo_2500mah_-_35/50c&chargestate=0&s=4&p=1&esc=max_20a&motor=turnigy&type=35|ntm2836-750&gear=1&propeller=0&propconst=1.3&proptwist=0&diameter=11&pitch=4.7&blades=2

Now the maddening thing is I can't get eCalc to build a config with long flight times, switching the 11inch props to 8's increases flight time but reduces hover time??? Seems like I'm doing something wrong with the tool or I don't understand motor/prop/battery relations :black_eyed:


Cheers


Tentative HK parts list:
Quantity Stock Product description Price Weight
3 T2450.4S.30 - Turnigy 2450mAh 4S 30C Lipo Pack $71.97
5 NTM2836-750 - NTM Prop Drive 28-36 750KV / 265W $79.95
4 017000055 - 8045 SF Props 2pc CW 2 pc CCW Rotation $11.16
4 017000054 - 8045 SF Props 2pc CW 2 pc CCW Rotation (.. $11.16
1 DL-Volt-Alarm - On Board Lipoly Low Voltage Alarm (2s~4s.. $2.15
1 258000011 - 10CM Male to Male Servo Lead (JR) 26AWG .. $4.75
4 9192000130-0 - Afro Slim 20Amp Multi-rotor Motor Speed .. $54.32
1 015000095 - XT60 to 4 X 3.5mm bullet Multistar ESC P.. $3.36
1 9171000202 - OrangeRx DSMX3 Spektrum Compatible DSMX .. $19.25
1 Prop-Bal - Turnigy Magnetic Precision Prop Balancer $12.95
4 NTM28-ACC - NTM Prop Drive 28 Series Accessory Pack $7.40
2 9171000015 - 5.6mm x 14mm M3 Nylon Threaded Spacer (1.. $3.76
2 OR009-00504 - M3x12mm Nylon Screws (10pcs/bag) $1.86
2 Turnigy-HKLP - Turnigy Battery Strap 330mm $3.18
1 9171000334-0 - Hobbyking KK2.1 Multi-rotor LCD Flight C.. $29.99
2 OR009-01502 - M3 Nylon Nut (10pcs/bag) $1.38

*I do own a dx6i and multiple cell charger

 

[William A]

Add KK2 flash tool (USBASP) and check out the Q-Brain ESC.

 

[FinalGlideAus]

If you have a KK2.1 you won't need to buy a low voltage alarm as the KK2.1 will do it.

 

[Mustang7302]

Even on a 4S battery, 750KV is pretty low and it puts you in some odd power to weight situations. A 8x4.5" prop will make ~95 watts of power (@6.5A), a 9x4.7" prop will make ~125 watts of power (@9.5A), and a 10x4.5" prop will make ~160 watts of power (@12A). Watts to thrust is not linear either. You will probably be looking at about 900 grams of all up weight, could be closer to a kilo, and that 95W from a 8" prop will be anemic while the 160W from a 10" prop will be way too much for the KK2.1 to cope with in its gains for power to weight. So the sweet spot is the 9" prop option which is unusual from most builds; it just isn't common to see a low KV motor spin a modest 9" prop.

There is an advantage here however; the more voltage you have the less current (amps) is needed to make the same power (watts), and current draw (amps) is what limits flight times. A 1200KV motor spinning a 9x4.7" prop on a 3S battery makes nearly the same power (watts), but it takes 13.5 amps to do so. In real world flight times with a 2200mAh battery, the 1200KV/9x4.7"/3S setup will see about 10 minutes of flight time where as the 750KV/9x4.7"/4S setup might run for 13 minutes of flight time. So 30% less current will yield about 30% more flight time.

So the benefit here is a desirable one, but why do most quadcopter setups only run on a 3S battery setup with higher KV motors with modest size props or considerably larger props on lower KV motors? There is a list of reasons, but I will focus on two: voltage and weight. A fully charged 4S battery is 16.8V in a world of "consumer" auxiliary electronics which were designed around 12V. Things like LED lights and FPV transmitters wont reliably cope with extra voltage for extended use, which is contradictory to the additional flight time you can get. You will need to run a 12V regulator off of your power harness which makes for more complexity, weight, and space occupied.

Weight is really the biggest factor here. That fourth cell is an exponential penalty in weight. For the 300 grams that the 4S 2450mAh battery weights, you could run a 3S 4000mAh battery which is a 35% gain in capacity. All of a sudden, that 1200KV/9x4.7"/3S setup is looking at 16 minutes of flight time for the same weight the 750KV/9x4.7"/4S setup runs for 13 minutes with less current draw (amps). So now the benefit of lower current draw is negated in real world performance.

A lot of this is theory based on my experience and the experience of others collected from the forum. There are exceptions to all of the above, but all of the above is based on the consideration of the modest size, weight, and materials of FliteTest frames. Reality is that FliteTest frames are not big, strong, heavy lifters; they're designed to be easily repaired and just big enough to allow the flexibility to get your feet wet in multirotor building. That being said, strapping a 300 gram battery is a lot of weight to the wood materials and adds a lot of inertia making the craft prone to damage in crashes; a level of damage which is more time and expense to repair. Breaking booms is easy enough and cheap to fix. Breaking motor mounts, landing struts, support plates all require new orders for replacement parts, and those repairs will add up over time.

Stick to being on the lighter side and not only is the craft easier to learn to fly, but it is more resilient on the parts which take abuse in crashes. If you're still considering the 4S setup, at least look at the lighter and shorter NTM Prop Drive Series 28-30A 750kv / 140w motors which saves 20 grams of weight per motor (80 grams on the craft). Also consider a smaller battery to help shed weight like a ZIPPY Compact 1800mAh 4S 35C. These two changes will get you down to 700 to 800 grams of all up weight which will still see 10 to 11 minutes of flight time.

Another thing to consider is the slim Afro ESCs do not have a internal BEC (battery eliminator circuit) which leaves you with no way to power the KK2.1 and your receiver without the use of an external BEC. So use the standard 20A Afro ESCs which will power the flight controller and receiver.

A tried and true 3S setup is as follows:
NTM Prop Drive Series 28-26A 1200KV
NTM Prop Drive 28 Series Accessory Pack
Afro ESC 20Amp
GWS Counter Rotating (RH) 9x4.7" Props
GWS Standard Rotating (LH) 9x4.7" Props
ZIPPY Compact 2200mAh 3S 25C Lipo Pack

 

[Cyberdactyl]

Awesome writeup Mustang.

 

[cranialrectosis]

Seriously, if you want to go 4S on a light quad, start here:
http://forum.flitetest.com/showthread.php?6274-Simple-light-amp-fast-Quad

+1 for Mustang.

 

[Cyberdactyl]

Thanks CR.

 

[Mustang7302]

Awesome writeup Mustang.

Thank you.

Seriously, if you want to go 4S on a light quad, start here:
http://forum.flitetest.com/showthread.php?6274-Simple-light-amp-fast-Quad

This kinda of build and power is not for someone's first build or two. Just shy of a kilo and >200W of power per motor is obnoxious. I would be interested to see Cyber post his gains in that thread.

I would be intimidated to fly something like that.

 

[Cyberdactyl]

I would be interested to see Cyber post his gains in that thread.

The tuning was terrible in the "quick throttle punches" video. Just something I popped in quick right after building it. Also, I had no expo at all on the transmitter and no stick scaling on either the tx or the card, so it was twitchy.

I've since tuned it pretty good, but can't recall exactly, (I'm at work) but, the stick scaling is around 70% for the pitch and roll, and 60% on the yaw. The expo for all is around 40%. The P gain is like 60. The I gain 95. The rest is like 50% of those, the I limit is like 15.

 

[cranialrectosis]

This kinda of build and power is not for someone's first build or two. Just shy of a kilo and >200W of power per motor is obnoxious. I would be interested to see Cyber post his gains in that thread.

I would be intimidated to fly something like that.

I concur. As you stated above, this build is NOT for a beginner. 4S adds complexities that require experience to overcome.

4S multirotors (and even higher) are reality. However, I would not build one as my first copter. If I were to build one, I would look hard at Cyber D's design.

 

[Matt_mg]

Awesome, clear writeup indeed! Back to 3s and 1200kv it is

 

[Mustang7302]

Looking over your parts list I noticed a few more things. The OrangeRX DSMX receiver you chose is only three channels; you'll need at least 5 for the KK2.1. Substitute for this receiver: http://www.hobbyking.com/hobbyking/...m_JR_DSM2_Compatible_6Ch_2_4Ghz_Receiver.html

You can also save on the few extra dollars in nylon standoffs and "hard"ware. I assume you're planning to use them to mount the KK2 to the center hub, which will stick the thing a half inch up on the surface with no vibration dampening. An alternate solution which solves these points, credit goes to CranialRectosis, is to use the head of 4" zip ties like seen below. You're going to need 4" zip ties anyways to tidy up wiring.

These pictures are from my iQuad build thread as seen here: http://forum.flitetest.com/showthread.php?6530-Mustang7302-s-iQuad-Build-Log/page3

 

[Matt_mg]

Looking over your parts list I noticed a few more things. The OrangeRX DSMX receiver you chose is only three channels; you'll need at least 5 for the KK2.1. Substitute for this receiver: http://www.hobbyking.com/hobbyking/...m_JR_DSM2_Compatible_6Ch_2_4Ghz_Receiver.html

You can also save on the few extra dollars in nylon standoffs and "hard"ware. I assume you're planning to use them to mount the KK2 to the center hub, which will stick the thing a half inch up on the surface with no vibration dampening. An alternate solution which solves these points, credit goes to CranialRectosis, is to use the head of 4" zip ties like seen below. You're going to need 4" zip ties anyways to tidy up wiring.

These pictures are from my iQuad build thread as seen here: http://forum.flitetest.com/showthread.php?6530-Mustang7302-s-iQuad-Build-Log/page3

Nice catch I was sure I had swapped the RX but apparently it's not the case... I was thinking of this one since my radio does DSMX http://www.hobbyking.com/hobbyking/store/__38392__OrangeRx_R800X_Spektrum_Compatible_DSMX_8Ch_2_4Ghz_TwinPort_Rx.html


Nice trick with the zip ties.