Too high of a COG?

[srbell]

I built a large quad with a WKm expressively for mapping and ended up with a flip of death machine. It's using a NEX5n, 6135 330 motors and two 8ah6s packs. Originally I tested without the camera and mounted the batteries under the frame and added the simulated weight of the camera as well. Flew amazing for 40min flying grids at 8m/s. Took the ballast off, mounted the camera on the bottom and mounted the batteries on the top of the frame. Nothing else changed except the cog setting in the assistant. Four flips, amazingly no damage except for some scratches on the propellers. COG is correct, motors and props are correct. The COG is about 1" below the propellers so it's not really top heavy. Is there a limit to how close your COG can get to the propeller plane? BTW, I've swapped out the flight controller, IMU and the GPS all with the same result. I found the speed controls were glitching on startup, so I've swapped them for different models and will retest tomorrow. Any thoughts?

 

[Anacaona]

I don't know if this could be your case, but I have heard that DJI released the new IMU V2 because of the problems they (we) were having with heavy rotors.

 

[Nobody2]

I built a large quad with a WKm expressively for mapping and ended up with a flip of death machine. It's using a NEX5n, 6135 330 motors and two 8ah6s packs. Originally I tested without the camera and mounted the batteries under the frame and added the simulated weight of the camera as well. Flew amazing for 40min flying grids at 8m/s. Took the ballast off, mounted the camera on the bottom and mounted the batteries on the top of the frame. Nothing else changed except the cog setting in the assistant. Four flips, amazingly no damage except for some scratches on the propellers. COG is correct, motors and props are correct. The COG is about 1" below the propellers so it's not really top heavy. Is there a limit to how close your COG can get to the propeller plane? BTW, I've swapped out the flight controller, IMU and the GPS all with the same result. I found the speed controls were glitching on startup, so I've swapped them for different models and will retest tomorrow. Any thoughts?

Put the Cog setting back to the original setting. Balance the bird, and you may have to move batteries around or add weight in one more arms to get the proper balance. Remember the Z setting is negative going above the IMU.

good luck!

 

[srbell]

No more flipping, but it's flying a little funny though. It's like it's overpowered for the payload. It seems to float lol. The props seem like they're barely moving, I guess that's why I can stay up so long. I may actually add two more 6s8ah packs to bring the weight up a for a auw of 6.5kg from the mid 4's. My thinking is if the propellers are turing faster, I may get a little better control and stabilization.

 

[leofuica]

SRBELL:

Your CG is more upper than the normal beacause of weight of your batteries

 

[srbell]

The other two pack will go on saddle mounts attached to the gear below the COG. It should be interesting what the flight time will end up being. Max thrust on these four motors is 14kg so at 6.5kg my hover is still under 50%. We'll see.

 

[gtranquilla]

The difference between motor torque and load torque defines the rate of motor/prop acceleration or deceleration. So focus on your motor torque capability to determine the speed at which your control system can respond.....motor speed is a secondary consideration such that a slow motor with higher torque will give you faster speed control response . http://www.etap.ca/products/motor-acceleration/

No more flipping, but it's flying a little funny though. It's like it's overpowered for the payload. It seems to float lol. The props seem like they're barely moving, I guess that's why I can stay up so long. I may actually add two more 6s8ah packs to bring the weight up a for a auw of 6.5kg from the mid 4's. My thinking is if the propellers are turing faster, I may get a little better control and stabilization.