Tested the co-axial quad x8 with both 15 inch(carbin nylon) and 17 inch(CF) propellers.
Motor- Tarot Martin 4008 330kv, All up weight : 4.5 kg
Observed a strange thing, The flight time in 17 inch was less compared to 15 inch…
Can anyone please explain why this happened ?
If I try 17 inch in a Quadcopter, will get more flight time compared to 15 inch.(10 mins of flight time difference)
Log files:
https://drive.google.com/drive/folders/1I2q8y8YdKhy5X0dmfxN-Uv9ZujMC99So
Propellers are not equal: some are more efficient than other, some are crap.
Do a test with the same brand and shape then post the result.
What I am not understanding is 17 inch produces more thrust than 15 inch…
But the current consumption is more in 17 inch
Why?
i think that just means the 17 are less suited to coaxial arrangement than the 15.
What you are experiencing is a property of the motors - they just cant turn the 17inch props well enough, there is too much load.
This is a typical mistake a lot of people make: thinking bigger props will give longer flight time.
It is quite important that components are properly matched.
If you really want more flight time or payload capacity you will probably have to change up the motors. That may need different ESCs and maybe even a different battery pack (which will be heavier) - and the calculations start all over until you reach a workable compromise…
Before you know it you’ve built a whole new copter and you dont have the old one left to play with 
And not everything is about flight time either - you need to consider stability. So what if you’ve fitted bigger props and now get 45mins flight time, but it’s so unstable that even a breath of wind turns your copter into a pile of expensive parts on the ground. Slightly smaller props spinning a bit faster would give the required attitude control to resist wind gusts and disturbances.
he said that the 17 in quad (non-coax) performs better than 15. so seems like the motors can handle it.
The same setup with quad configuration gives 30 mins in 17 inch.
But in co axial gives 23 mins…
It’s unlikely you’ll ever get more thrust for free, so there will likely be more current draw.
A 17inch prop would likely have more drag than a 15inch prop, leading to more current draw.
There’s inertia to deal with too, when constantly changing RPM, leading to more current draw.
It is typical for a motor to only work properly with a narrow range of props.
There’s also the matter of control: you need the motor to be able to slow down that prop and also instantly speed it up too, all within a couple of revolutions. It’s not like a fixed wing motor where you set a constant RPM and away you go.
Notice how when you do successfully use bigger props, it’s with a bigger low kv motor, that costs a lot more too, and operates off say a 12S battery instead of 6S. It might even appear to have a lower current draw, but remember it’s got double the voltage to work with and is probably dissipating twice the electrical power.
I’m not understanding now…
The same quadX8 but with either 15inch or 17inch props, or quad format??? I’ve lost track of what configurations you are comparing.
This would be believable. It’s rare to just put on bigger props and get more flight time of the original configuration was well matched.
Yes @xfacta
The overall current is more in 17 inch compared to 15 inch.
In quad config the average current consumption is 15-16 A
In coaxial
15 inch - 21-22 A
17 inch -22-23 A
Yes, so your 17inch props are actually doing quite good compared to the 15inch. You may be able to have a bigger payload but get a bit less flight time. Those numbers are nothing to worry about, and should be expected.
Probably just monitor your motor temperatures.
Need Help !!
Just saved from a crash
EKF3 IMU0 MAG0 ground mag anomaly, YAW -Realigned
EKF3 IMU1 MAG0 ground mag anomaly, YAW -Realigned
EKF3 IMU2 MAG0 ground mag anomaly, YAW -Realigned
Log file :
https://drive.google.com/drive/folders/1XituHLgmXMXvgQ9hqKVUtU8Wzl3uTLwA
PS: CUBE ORANGE FLIGHT CONTROLLER WITH KORE CARRIER BOARD…
Z axis vibrations are less than ideal, that will affect tuning. So if you can improve the vibration isolation of the flight controller, make sure nothing is touching or pulling on it and all wiring is secure - That will help.
You can see pitch and roll control is a bit noisy and it seems to start getting a bit worse over time. Oscillations are appearing.
The oscillations become bad and attitude control is almost lot - you did well to get it landed. Some people would probably try lots of pitch and roll stick inputs and make it worse.
I think it’s just poor tuning (no tuning started yet) and maybe wind increased.
It would be good to know if motors were getting hot with those 17inch props.
Set these for general tuning and safety, with your copter in mind
BATT_ARM_VOLT,22.10
BATT_CRT_VOLT,21.00
BATT_FS_CRT_ACT,1
BATT_FS_LOW_ACT,2 or 3
BATT_LOW_VOLT,21.60
BRD_BOOT_DELAY,3000
FENCE_ENABLE,1
GPS_GNSS_MODE,5
GPS_GNSS_MODE2,5
INS_ACCEL_FILTER,10
INS_HNTCH_BW,25
INS_HNTCH_ENABLE,1 ← set this then refresh to see the rest
INS_HNTCH_FM_RAT,0.7
INS_HNTCH_FREQ,50
INS_HNTCH_MODE,1
INS_HNTCH_REF,0.16
INS_LOG_BAT_MASK,1
INS_LOG_BAT_OPT,4
MOT_BAT_VOLT_MAX,25.20
MOT_BAT_VOLT_MIN,19.80
MOT_SPIN_MIN,0.12
These PIDs might be a good start
ATC_ANG_PIT_P,6.5
ATC_ANG_RLL_P,6.5
ATC_RAT_PIT_D,0.005
ATC_RAT_PIT_I,0.12
ATC_RAT_PIT_P,0.12
ATC_RAT_RLL_D,0.005
ATC_RAT_RLL_I,0.12
ATC_RAT_RLL_P,0.12
and these will settle down the position controller, for example Loiter mode wont try to hold a wandering GPS position so strictly
PSC_ACCZ_I,0.4
PSC_ACCZ_P,0.2
PSC_POSXY_P,0.5
PSC_VELXY_D,0.25
PSC_VELXY_I,0.5
PSC_VELXY_P,1.0
As with any of these changes, start in Stabilise mode and if there’s any oscillations land immediately and reduce the ATC_ANG_PIT_P and ATC_ANG_RLL_P values by nearly 50%.
If everything seems OK change to AltHold and try some gentle pitch and roll movements.
You dont have to go all aerobatic or run missions, this flight will just gather data for more changes.
Actually we were upto tune the copter…
I am using dual GPS here3 and using two external compasses.
One of the compass mag field is to high soon after taking off.
I have attached the picture along…
But if I disable that compass which has high mag field the flight is ok…
Did I get the error due to my compasses…
The flight video link after disabling one of the compass for reference @xfacta
https://drive.google.com/file/d/1YEHZ8mCykmyG2XyJ499agV785o0G84Bu/view?usp=drivesdk
That’s a Li-Ion pack I guess. That can be trouble close to a compass.
@dkemxr
Yes Li on, actually for flying we use a bigger 12.6ah battery…
One of the compass mag field will jump to 800 soon after tafe off…
