Tiger-Motors U8 + 28x9,2 props

Q

Quinton

Active Member
R_Lefebvre said:
Yes, but you have to remember that on most DJI flight modes, the throttle stick position has absolutely no connection to the actual motor throttle output. I think too many people actually don't know this, and I don't understand why. This is why we have so many people who come try Arducopter, and then find out that their flying throttle is over 80%, which we consider unacceptable as it leaves little margin for flight control.

When in DJI GPS mode, you simply give it 50% stick, and it will fly. It will output 10%, or 90% throttle, whatever it takes to fly.
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I do understand DJI GPS mode, I just did not understand how it would work with a machine this light and so powerful as it may have got confused, that is why I always assumed Ferdinand was flying in manual mode and never GPS
The hover (take off) speed imagine is pretty close to just starting the motors on the ground if the MR is very light.
So basically its exactly the same, if you are at 50% throttle it will hover, if you go lower you will descend, higher you will go higher (as long as the power is there)
 


A

ACP

Member
Ferdinard's video of an x8 taking off from a flying x16 is actual very interesting. Not just a stunt, it actual proves the capable reaction speed of large props and low KV.
When the x8 takes off there is a sudden load drop from the x16. Note how the x16 holds it's altitude and stability so well!!!!
If the "reaction speed" of large props / low KY was so bad then the x16 would have suddenly increased altitude in an unstable manner.

Well done Ferdinard.

Also the WKM and A2 has an Idle state setting which is user adjustable in the Assist software.

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This is used by the algorithms to work out a starting point for the ESCs and take off.

I think I am actual going to go with the U11 120Kv on 12S as this appears "on paper" to be the best fit all round for the "LiPos" and AUW I have.
 

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FerdinandK

FerdinandK

Member
I the german forum someone did a test with equal props and adjusting the motor mixer for optimal efficiency / balance between top and bottom. Test were with 15" props (28" results will be different). The best result for efficiency was 90/100 the best balance was at 95/100. The difference in balance to 100/100 for balance (of current) was <2% the difference in overall efficiency was <3%

The most important thing on DJI X8 is NOT to use CW an all of the top (and CCW on all of the bottom) propellers. Here you have to mix on top and bottom plane, otherwise you can have all kinds of difficulties (YAW, performance loss, ...) especially in combination with motors not strictly horizontally. Here you can use a custom mixer, or just ignore the top/bottom in the DJI X8 mixer and only respect the CW CCW for motor connections (but place them on top like a quad and on bottom inverse)

best regards
Ferdinand
 
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Q

Quinton

Active Member
FerdinandK said:
I the german forum someone did a test with equal props and adjusting the motor mixer for optimal efficiency. The best he could get was with 100/94 (if I remember correctly) but the gain in performance was only about 3%.( compared to 100/100). Also this was done with 18" props, the result with 28" I assume to be different.

The most important thing on DJI X8 is NOT to use CW an all of the top (and CCW on all of the bottom) propellers. Here you have to mix on top and bottom plane, otherwise you can have all kinds of difficulties (YAW, performance loss, ...) especially in combination with motors not strictly horizontally. Here you can use a custom mixer, or just ignore the top/bottom in the DJI X8 mixer and only respect the CW CCW for motor connections (but place them on top like a quad and on bottom inverse)

best regards
Ferdinand
Click to expand...

Yeah we discussed that before on the CarbonCore thread, it is setup just like this..

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Q

Quinton

Active Member
Interesting he ended up at 93/100
I do have a Carboncore cortex here that has 15x5 on toop and 16x5.4 on bottom, I tried it with 15 on top and bottom but it did not fly as good.
I rem Kopterworx said that it is not good to fly with DJI FC and different props top/bottom, just wondering if they had a play around with the motor mixers.
Just wish I had better data logging like on the Herkules or something else, telemetry really is key to getting the best setup possible.
 

A

ACP

Member
Well a parcel arrived today. 8x t-motor U11 120Kv, 8x 28" props and 70a Pro ESCs.
Man are those motors big. I hope I have made the right choice .

As an experiment I tested one of my x4s today. Usual runs on 4x 480kv @ 4s. I added another pack in series so 8s.
The idea was to see what the WKM did with too much power.

Flight wise it was very stable. However Landing and takeoff was hard. It had trouble slowing the motors down enough to land. And as soon as the motors start up the quad hovered about 6" even with throttle / altitude set to 0.

Ok the only added weight to the quad was an extra battery.

The motor / prop combo can carry upto 60Kg, I intend to have an AUW of 20kg.
The reason I went tor the 120KV was I could not find a happy balance of motor to prop out of the U range to match my payload and LiPo packs. 6s was not enough as advised earlier in this thread. 12s overloaded the other motors power wise with the t-motor props available in the UK ( 28", 29 "). With the next size down 18" on 12S, not enough thrust for safe maneuverabilit.

Hence the choice to go for the U11 120Kv on 12S. The thing i'm worried about is it can hover at 12 to 15% throttle @ 20Kg.

This is very low. I can't increase payload as I'm only licensed to up to 20Kg until mid next year when I get my <150Kg licence.

I suspect I will have to purchase some 22,000mah 4s until then if I have too much power with this setup.

I will keep you posted.
 
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Q

Quinton

Active Member
Just a quick thought, has anyone ever tested this setup with the motors placed underneath the boom instead of on top of it.
I read somewhere that this could be upto 8% more efficient.
 

A

ACP

Member
Quinton
Just a quick thought, has anyone ever tested this setup with the motors placed underneath the boom instead of on top of it.
I read somewhere that this could be upto 8% more efficient.​
Click to expand...

Not sure what you mean by this. With an x there is one motor on top of the boom and one on the bottom.
 


A

ACP

Member
I can't see any reason having the motor underneath the boom improving the efficiency. unless the boom is shaped as an airfoil designed to improve the air flow into the prop.
 

Old Man

Old Man

Active Member
Mounting the props under the boom would be akin to using a pusher configuration on a high drag airplane. Not as bad but having a similar effect. Efficiency with such an arrangement would be sacrificed if there were not also motors/props above to "cone" through the lower propeller arc.


Sent from my iPhone using Tapatalk
 

B

bruce365

Null
It is well known that an obstruction to the airflow after it goes through the propeller reduces efficiency slightly more than in front of the propeller (as long as the obstruction is the same distance and size from the propeller e.g. the copter arms)
regards - bruce
 

W

Waladi

Member
What kind of material for the frame that your going to use?

Is it Carbon Fiber >25mm or aluminium?
Any Supplier recommended?

Thanks.

ACP said:
Well a parcel arrived today. 8x t-motor U11 120Kv, 8x 28" props and 70a Pro ESCs.
Man are those motors big. I hope I have made the right choice .

As an experiment I tested one of my x4s today. Usual runs on 4x 480kv @ 4s. I added another pack in series so 8s.
The idea was to see what the WKM did with too much power.

Flight wise it was very stable. However Landing and takeoff was hard. It had trouble slowing the motors down enough to land. And as soon as the motors start up the quad hovered about 6" even with throttle / altitude set to 0.

Ok the only added weight to the quad was an extra battery.

The motor / prop combo can carry upto 60Kg, I intend to have an AUW of 20kg.
The reason I went tor the 120KV was I could not find a happy balance of motor to prop out of the U range to match my payload and LiPo packs. 6s was not enough as advised earlier in this thread. 12s overloaded the other motors power wise with the t-motor props available in the UK ( 28", 29 "). With the next size down 18" on 12S, not enough thrust for safe maneuverabilit.

Hence the choice to go for the U11 120Kv on 12S. The thing i'm worried about is it can hover at 12 to 15% throttle @ 20Kg.

This is very low. I can't increase payload as I'm only licensed to up to 20Kg until mid next year when I get my <150Kg licence.

I suspect I will have to purchase some 22,000mah 4s until then if I have too much power with this setup.

I will keep you posted.
Click to expand...
 

A

ACP

Member
What kind of material for the frame that your going to use?

Is it Carbon Fiber >25mm or aluminium?
Any Supplier recommended?
Click to expand...
#

This will be an all Carbon fiber construction.
The booms will be 50mm at it's widest point.
This is a custom build so no pre-constructed parts are being used.
I may throw together a basic H-frame using 40mm or 30mm Carbon tubes to test the setup first though.
 

D

Dragonrider

Member
Hi Anthony,

This is indeed a great thread and we too are looking at options for 15-20kg AUW.

The New Gryphondynamics Superframe looks amazing and booms attach and unattached easily for transport. I've heard X8 costs around 10% in efficiency but handles crosswinds better, motor failure well, and smaller footprint of course.

Since we're looking to fly a RED Epic, camera + MoVI gimbal our weight is high...10kg+ without copter. Hoping we might connect with someone else in Chicago to consult on our build...

Thanks to everyone for their informative posts...great community here.


ACP said:
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
Click to expand...
 

A

ACP

Member
Hi Dragonrider, You are right, this is a good forum. I don't tent to use forums very much but this one is the best I have found and there are knowledgeable / sensible people on here genuinely trying to help each other.
I have found on with many other places people trying to make a living out of flying like me, tend to keep there mouth shut and won't help. In some ways this is understandable as again like me, a lot of money has been spent on R&D developing our systems. I alone have invested well over £150K in this. But at the end of the day we are a small community in the big world and we are all trying to make the best systems in the safest manner, so sharing our knowledge can only be for the good of the whole community.


One thing to point out about the U11 is there weight. It's all very well seeing the figure if 730g per motor but when you pick one up it just sinks in how heavy they are. 8X 730g = 5840g for motors alone. by the time you add Lipos and frame you soon gobble up your AUW of 20Kg. I have now ordered in a bunch of 22,000 mah 2cells as I have a load of 22,000 6 cell. The 22,000 6s are 2509g so running at 12Cell like I originally intended would be 5017g that's 10.85KG just for the power system, leaving only 9.1Kg for frame and payload. Also the 120kv motors will hover a 20kg at about 12% throttle on 12 Cell meaning the FC has to have very fine control over the motors.

Today my order of 50x1m aviation grade Carbon fiber arrived, so next week once my molds cure properly I will try pulling a frame and test these besets of motors.
I will let you all know how they perform soon.

Thanks
Anthony
 

D

Dragonrider

Member
Hey Anthony,

Thank you kindly for responding. I know all too well the cost and tribulations of building a production based business and completely agree with the points you made. While I'm extremely technically adept, I've been out of the RC scene for a long time and so am treading softly while getting a handle on where things have come since... I know our Camera and Gimbal payload (and associated focus, video transmit etc) won't come in at less than 22 pounds or so, and of course I'd like to get an extra 3 pounds in case a DP wants a Cooke lens, or something else comes up we haven't anticipated. My hope was to keep the footprint of this beast smallish - around Cinestar HL size so we could pull off tight close shots of talent holding the bird as a camera rig for part of a shot, and then letting it go as can be seen on that MoVI M10 BMW video out there. That said, with this much weight, we keep getting nudged towards giant frames (the new Gryphondynamics Superframe is nearly as tall as the engineer who designed it - without props!) and so I'm a little stuck right now - between an overpowered smaller frame with lower weight tolerances, or an unwieldy giant frame with power to spare but significantly less portable and dynamic in function. Perhaps my dream of a smaller more manageable "floating jib" is not possible with today's technology? I had set my hopes firmly on the mythical Freefly Synapse FC system, but after waiting nearly 2 years for it to be released, and no sign at all that it's even a priority any longer, am looking at other FC options - all of which have their own upsides and downsides lol.

To make matters worse, I can feel the industry evolving at an almost daily record pace, so am concerned about making a significant investment, only to regret it a few weeks or months later. Yes, I know, one can easily wait one's life away for "perfect" technology and the one's who win are the ones who do what they can with what they have. That said, it's still a very interesting time to be working on this project and your hard won expertise (and anyone else who cares to weigh in) is *very* much appreciated.

My sincere thanks again for posting and making me feel welcome here. Have a great evening!

Warm Regards,

DR



ACP said:
Hi Dragonrider, You are right, this is a good forum. I don't tent to use forums very much but this one is the best I have found and there are knowledgeable / sensible people on here genuinely trying to help each other.
I have found on with many other places people trying to make a living out of flying like me, tend to keep there mouth shut and won't help. In some ways this is understandable as again like me, a lot of money has been spent on R&D developing our systems. I alone have invested well over £150K in this. But at the end of the day we are a small community in the big world and we are all trying to make the best systems in the safest manner, so sharing our knowledge can only be for the good of the whole community.


One thing to point out about the U11 is there weight. It's all very well seeing the figure if 730g per motor but when you pick one up it just sinks in how heavy they are. 8X 730g = 5840g for motors alone. by the time you add Lipos and frame you soon gobble up your AUW of 20Kg. I have now ordered in a bunch of 22,000 mah 2cells as I have a load of 22,000 6 cell. The 22,000 6s are 2509g so running at 12Cell like I originally intended would be 5017g that's 10.85KG just for the power system, leaving only 9.1Kg for frame and payload. Also the 120kv motors will hover a 20kg at about 12% throttle on 12 Cell meaning the FC has to have very fine control over the motors.

Today my order of 50x1m aviation grade Carbon fiber arrived, so next week once my molds cure properly I will try pulling a frame and test these besets of motors.
I will let you all know how they perform soon.

Thanks
Anthony
Click to expand...
 

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