diagnosing flight problems

[queglay]

Hello, This is my first post. I have been flying the phantom for 6 months.

I have spent a fair bit of money to fix the flight problems I've been having recently but without success so far. I'm hoping you might have some sugesstions here.

I have mounted tiger motors on and carbon props and have had great flights until a crash which im still recovering from.

I replaced the props and shafts, and it flys well in all directions except trouble on ascent and descent which is very unstable. the phantom for a while has also had trouble staying stationary in GPS mode. I have calibrated the gps and updated the firmware.

Even though I replaced the shafts, some appear to have slight wobble when i observe them on the ground, and i wonder if this is the problem. are my motors now garbage from that accident? i would suspect that if i can observe wobble that I may not even be able to rebalance the motors if this is the result of a deformation in the motors themselves.

I also wonder if the compass could be broken, and have ordered a replacement of that too.

Thankyou for any sugestions, any help would be appreciated!

 

[tanasit]

After the crash, many parts can go wrong but you can identify each by some simple test.

Too check if the motor shaft bend, turn one tip of the prop to position over the arm and note the gap or space between the blade tip and the top surface of the shell. Next turn the other tip around and see if the gap is of similar distance? If not, the either the shaft is bend or the hub hole is not true but most likely the shaft!
Or you can remove all the prop and in stall only the prop nut, then run the motor and see if the tip of the prop spin in place?

The carbon props prefer heavy load other wise you may get slight wobble in up/down flight.

GPS mode can only keep your Phantom within a few square yards NOT on a dime.(see Phantom spec for exact number).

The compass can be tested by performing the CL, if it works accordingly then the compass is fine.

 

[tanasit]

The carbon props prefer heavy load other wise you may get slight wobble in up/down flight.

Why?

When I used carbon props I did not experience that behavior.

The stiffness of the carbon together with the airfoil will give the faster response to the control than the stock plastic ones. Plus if you have a stock Phantom with no other pay load, then the wobbling, swinging MAY occur depending on the GAIN settings similar the the tail fishing on the RC helicopter when the gyro setting is over sensitive.
I did try the 9x4 carbon prop on my stock Phantom and the wobbling is obvious, no matter how I change the gain setting so I add another battery pack to the landing gear, the wobbling is gone!

 

[tanasit]

When Phantom first came out, there was no EXACT 8x4.5" carbon prop but 9x4.7 with 6mm hole while Phantom motor has 7.9mm shaft (not 8mm did you know that?), not to mention the unique "key" in the hole to match the motor shaft. So most people will use the prop reamer for the job, as a result the hole is too large and won't fit snugly.
I used the Dremel tool to shave down the 8mm portion of the reamer for this purpose. And as I mentioned earlier that the 9x4 carbon prop didn't give me stable flight for my "stock" Phantom, so I cut the prop down to 8x4 and shape it to exact the same stock air foil:

I also tested many other plastic props that I could find and found the result below:

Prop time (min:sec.) sound (dB)
Stock 12:48 83
Graupner 12:40 84 adjust throttle a few times
GWS 13:39 83
MasterAS 8:33 84.5
APC 10x3.8 cuttip 13:54 84
Gemfan 9x4.7 14.06 86 stable, hold atti well
APC 9x4.5 oscillation!
FC 3-9x4.5 11:31 92 adjust throttle 2 times
FC 9x4.5 11:42 90 stable, hold atti well
Gemfan 9x4.7 14.22 86 stable, hold atti well Nano-Tech A-Spec 65-130C
Carbon 9x7 13.29 90 slight oscillation (reduce Pitch & roll to 80%)

And yes I tried the 9x5, 9x4.7, 9x4.5 but for the most part, the stock prop is still the best.

 

[queglay]

Thank you everyone.

could there be a problem with an accelerometer to cause this? is that stored in the Naza up the top of the craft?

I have also ordered a bearing for my mt2216-11 motor that has a bit of wobble in the shaft. I will also measure the distances for the props, that's a neat trick, thanks!

 

[tanasit]

Thank you everyone.

could there be a problem with an accelerometer to cause this? is that stored in the Naza up the top of the craft?

I have also ordered a bearing for my mt2216-11 motor that has a bit of wobble in the shaft. I will also measure the distances for the props, that's a neat trick, thanks!

Did you balance the props?

I don't think the accelerometer is defective otherwise you won't even be able to hover.
However the accelerometer has been known to get stuck after the crash and the simple fix is to verify this by checking its values on the Assistant (Tools tab), then if it stuck, remove the NAZA and gently tap one corner on the table, then you can check it again.

Even though everything is working, descending may show some wobbling anyway, especially when you take it directly straight down because the rotors are coming down the column of downward moving air aka "bad air". People who take video clips avoid this by coming down at slight angle.

If the props are too large and the Phantom is somewhat light, then you may also see it wobbling but you can test by adding weight (another battery pack strapped to the landing gear), and see if the wobbling goes away.