Tiger-Motors U8 + 28x9,2 props

[renaudbarbier]

hello

I a running different setups of U8 and fund it difficult to setup.
I am using 6S batteries and tried the following setups:
- 135kV - 6S - 29"
- 135kV - 6S - 26"
- 170kV - 6S - 26"

all are X8 config with dji a2.

135kV 26"runs ok in light wind but not ok above 8-10knots (wobbles and almost crashes)

rest config are not working. it seems that a2 can not manage the stabilization with such low rpm. do you have similar feedback?

I need to get big ESC to test 8S...

 

[srbell]

I'm finding even with the Foxtech 5108's 280kv and 18" props prove problematic with the DJI. One thing I know for sure, the esc you use is really important. SimonK firmware seems the best, but you'll run into sync problems....with just about every combination. I've suffered the odd flip from motors stalling. The latest SK firmware V2014-3-6 seems to run perfect, even with the pixhawk autopilot (seemed to be the worst of my systems). Non SimonK is just plain awful! Like you're skating on a ball of ice lol! Twitching and drifting all over the place. You may want to try the Pixhawk as well as there's a lot more parameters you can adjust to get a stable setup. Such large propellers and low KV motors were never on DJI's radar in their development. They make controller to run 8-15" propeller : ) That's not a fact, but just my gut feeling. Still have yet to jump into the U8 size, but the 5108's are pretty close to the U8's efficiency so it's a good test platform. Eventually I'm thinking of modifying a Kraken 130 into a 1600mm Hex with U8 (or Foxtech versions) and 28" props.

hello



I a running different setups of U8 and fund it difficult to setup.
I am using 6S batteries and tried the following setups:
- 135kV - 6S - 29"
- 135kV - 6S - 26"
- 170kV - 6S - 26"

all are X8 config with dji a2.

135kV 26"runs ok in light wind but not ok above 8-10knots (wobbles and almost crashes)

rest config are not working. it seems that a2 can not manage the stabilization with such low rpm. do you have similar feedback?

I need to get big ESC to test 8S...

 

[FerdinandK]

@rendaubarbier
What gains are you using? If your basic gains are too low it feels like that. Basic gains with standard ESCs should be somewhere at 250-300 for Roll and Pitch.

@srbell
I am flying 10" to 28" setups all standard ESCs (no Simonk) and this is really no problem also in windy conditions and fast forward flight. Also you will be surprised what a different it will be if you swith from 18" to 28".

best regards
Ferdinand

 

[renaudbarbier]

@rendaubarbier
What gains are you using? If your basic gains are too low it feels like that. Basic gains with standard ESCs should be somewhere at 250-300 for Roll and Pitch.

@srbell
I am flying 10" to 28" setups all standard ESCs (no Simonk) and this is really no problem also in windy conditions and fast forward flight. Also you will be surprised what a different it will be if you swith from 18" to 28".

best regards
Ferdinand

basc gain is 180. attitude is quite low at 60, anything above generates oscillations!

 

[renaudbarbier]

I'm finding even with the Foxtech 5108's 280kv and 18" props prove problematic with the DJI. One thing I know for sure, the esc you use is really important. SimonK firmware seems the best, but you'll run into sync problems....with just about every combination. I've suffered the odd flip from motors stalling. The latest SK firmware V2014-3-6 seems to run perfect, even with the pixhawk autopilot (seemed to be the worst of my systems). Non SimonK is just plain awful! Like you're skating on a ball of ice lol! Twitching and drifting all over the place. You may want to try the Pixhawk as well as there's a lot more parameters you can adjust to get a stable setup. Such large propellers and low KV motors were never on DJI's radar in their development. They make controller to run 8-15" propeller : ) That's not a fact, but just my gut feeling. Still have yet to jump into the U8 size, but the 5108's are pretty close to the U8's efficiency so it's a good test platform. Eventually I'm thinking of modifying a Kraken 130 into a 1600mm Hex with U8 (or Foxtech versions) and 28" props.

I had problem with RCtimer NFS45 simonk. they give a "poke" sound in the motors like spark... went back to Tmotor T40A

 

[Luc Maximilien]

@ FerdinandK
Hello, I'm always very impressed by your achievements , compliments !

I follow you since a bit of time and I would like to ask you something, it is not a critic just to understand why things happens:

It seems that with the frame (and everything else except motors and props) your X8 weights , 2900 g , since , 8x U10 + 28" props weights 2800 g plus 300 g for the 8x Esc, right ?

Sincerely I would had expect a better efficiency from this combination of U10 and 28" props, because if I'm not wrong, with 1500g x motor, you are around 13,3 g x Watt while from specs I thought it should be around 17g x Watt :

Is it the coax setup that affects so much the efficiency ?
Or there might be some other reasons i.e. my bad maths ?

 

[FerdinandK]

Results on a test-bench are always to be questioned (especially if I made them, I am no expert on test-bech and measurements), since you never have 5m free space in front and rear space of the propeller, so what you measure is only an indication. On the test-bench there was only a single propeller mounted, but of course the coax eats some of the efficiency. Also in the video there where quite windy conditions. But from my point of view, 13gr/W on the copter with payload and reasonable flighttime is not bad.

best regards
Ferdinand

 

[Luc Maximilien]

Thanks for the reply Ferdinand,
In my experience a 10% error from bench to real world it is quite normal (always less performance).
I guess that the other lost efficiency could be due to wind conditions but the most from coax configuration .

Did you test Foxtech 28" props ?

 

[FerdinandK]

My (flight-) data says, that the coax "effect" is 10%, (but the 10% you would loose again if you think of the weight of a flat-octo frame (2m diameter)).

The foxtech prop I do not have right now, but possibly they will come soon.

best regards
Ferdinand

 

[fltundra]

Ferdinand,
Have you seen these?:tennis:

 

[Luc Maximilien]

@ FerdinandK coax is for sure the smart solution for ockto with large props.
my remark was only for the purpose of investigate the difference between bench test and real flight .

@fltundra I wrote to that company, they claim an incredible efficiency of 15 grams watt with a 85 g motor 510kv and a 14" propeller @42W with 4S battery.
A lot more than the best combination of motor and prop of that class I have ever seen.
They do not say the brand and type of the propeller, may be the miracle is there...

 

[fltundra]

@ FerdinandK coax is for sure the smart solution for ockto with large props.
my remark was only for the purpose of investigate the difference between bench test and real flight .

@fltundra I wrote to that company, they claim an incredible efficiency of 15 grams watt with a 85 g motor 510kv and a 14" propeller @42W with 4S battery.
A lot more than the best combination of motor and prop of that class I have ever seen.
They do not say the brand and type of the propeller, may be the miracle is there...

I have those motors and with out my camera and gimbal, she hovers at 3.5 amps per motor at 2120grams. Loaded with the gimbal draw, 3.8 to 4 amps 2515g. those KDE spec's are with tmotor cf's. I am running 14x4.8's:tennis:

 

[FerdinandK]

... this means 16A at 15V which is about 10gr/W (not 15)

 

[stitch1615]

You gentlemen are amazing but this is way too much science for me.
I just want to fly it.
If I get it to take off and stay in the air for 15 min, or before my legs give out, I'm a happy flyer.
Keep up the weird science. I'm sure you are helping lots of people.
I'm just too stupid, or lazy, to take advantage of it.

I will say this,,, I put my newest build on the e-calc and it said I might get 8 min of flight.
I entered all the exact figures in all the boxes.
In actuality, I got over 20 min, (my legs gave out), before bringing it home and never got a battery warning.
Naza, Tarot 650, 4830-420 Multistar, 45 amp Multistar ESC, w/ 14.4 APC props and 8000 4S 30C battery and I swear it will lift a refrigerator.

It seems I don't understand the e-calc or the science and apparently got lucky but, I'm happy with the results.
It doesn't matter much because the way things are going here in the USA we'll probably be shot down soon anyway unless you fly in your living room.

Anyway, I just wanted to congratulate you guys on your achievements.

 

[fltundra]

... this means 16A at 15V which is about 10gr/W (not 15)

9.6 to be exact, do you think if i go to the 3510 475kv's would it be worth the effort? I have been focusing on so many other things, and did'nt realize how far off the efficiency numbers are. The thrust and amp draw are real close. 22 min's on 4S8000mah no lower then 3.7 under load with 3 axis gimbal.

 

[ACP]

Cinistar 8 replacement

This is a fascinating thread which I have been reading over and over again.
I have to build a supper efficient system to replace my Cinistar 8.
I an torn between 8x 100KV to 170KV setup
I am also torn between 8 Flat and 8x configurations. Size and transport is no issue for me. What is important to me in order is:-

Decent recover-ability from a motor / ESC / Prop fail.
AUW 10KG to 20 KG
Good flight time.

I also have a time limit but have been banging my head against a brick wall with the above two depositions.

I am leaning towards the U8 Pro 170Kv / 28" props because I have a LOT of 6S 16,000 mah packs and to add 2s to this for the lower Kv is a pain.
I have lost a motor on the Cinistar (which is an 8 flat) a couple of times and managed to land safely, but have no experience with a X configuration setup.
I have also read many, many threads about 8 flat vs 8x but most people simply swear by what they have, about 50%/50%
I am encouraged towards the 8X setup from what I have seen and read simply because, it works and is efficient enough for a reasonable job.
The concern though is many people suggest using a larger that calculated prop on the bottom motor to compensate. However if i'm using T-motor 28" up top then I would need 29" below. I can't find a uk distribute for the 29" prop.
I also don't know the math involved with x setups but i see the logic in 28" up and 29" below, but can't find an example of a Multi with this configuration except the BIG HAMMER but I can't tell if the props are different sises.

Any advice or "push" towards any of these decisions would be most appreciated.

Thanks
Anthony

 

[FerdinandK]

on 14" copter you can choose flat or X8, but with 28" props? If you wanna use a car (and not a truck) to transport the copter, then a X8 is the only choice. flat would require 2m m2m-distance. I am using the same props on top and bottom, and most of people who tell you something different have never flown 28" coax (and if you use different props, the lower prop should be smaller with more pitch).

best regards
Ferdinand

 

[ACP]

Ferdinand Thank you very much for your reply.
Since I posted about 4 hours ago I realized it would be an easy test to quickly modify my Cinistar 8 Flat to a 8X configuration.
I did NOT take off the extra 4 booms, just left them on for speed.
I was VERY presently suppressed at the results.
Setting up the 400KV motors apposing each-other and flipping the 15x5 props over for the lower motor.

All in all there was precisely ONLY an 8% efficiency loss.

I was very surprised, I was expecting something like 15% to 20% loss from what others have suggested.
I think one thing that others probably have not taken into account is the DROP in amps in the lower motor.
Fortunately my setup can monitor all stats in all the ESCs and there was a 10.5% drop in amps at 50% and a 8.32% drop at 100% power (ok not power rather Pwm)

8x Config	Top Motor	Bottom Motor			Top Motor	Bottom Motor
	CW	CCW			CCW	CW
	AMPS	AMPS			AMPS	AMPS
50%	7	6.615		50%	7.02	6.602
100%	23.3	22.0239		100%	23.3	22.0165
	Flat Config	Flat Config	8x Config	8x Config
	Thrust in g	Total amps	Thrust in g	Total Amps
50%	11920	56	9720 <tbody> </tbody>	48
100%	27760	186.4	25200	172

<tbody>
</tbody>

 

[ACP]

Actual it's better because at 50% Pwm it is a 6.43% loss. This is not far off 12Kg which is close to my total AUW.

 

[Quinton]

Actual it's better because at 50% Pwm it is a 6.43% loss. This is not far off 12Kg which is close to my total AUW.

Can you share some details in your setup how you are monitoring everything, the thrust difference is very interesting.
How exactly did you calculate the thrust?
So an x8 config also has about 18% less thrust at 50% and 9% at 100% than a flat config, what props did you use top/bottom.