Balancing Props Against the Other 3 Props

[solentlife]

Balancing the blades of say a remote controlled helicopter is required to prevent vibration. However, it’s slightly different having four blades as they have the effect of cancelling each other’s inaccuracy in weight out.

If you have noticed vibration during flight then the chances are you have either previously crashed and bent something or the props are not attached correctly.

Also as others have said, the flight controller and ESC’s will distribute power as required thus ironing out any major issues.

Don’t get me wrong, balancing the props is never a bad thing and if anything could reduce the stresses on not only the motors but possibly on the shell too - also potentially reducing the known issue of random cracking around the motor bolts.

Just my two cents.

I don't say you are wrong ... but if you see a Heli with out of balance blades - it can do far more than just vibrate !

The Multi-Rotor ... in our case 4 rotors .... is controlled by Flight Controller that has input from Accelerometers and other data - this tells it what attitude and pitch the MR is in. It then alters the RPM by power applied to each motor. The 'problem' is not cancelled out - its compensated for.
The major item to affect this is any damage to PITCH of the blades - this directly affects the Lift Factor of the prop at RPM.
A lesser but still viable item is weight. If a prop weighs more on one arm - that arm will require slightly more power to compensate, but usually the weight of each prop are so close as to be discounted.

The matter in discussion though is balance of each prop and then in relation to each other. An out of balance prop causes the plane of rotation to oscillate, basically instead of a flat plane - the prop flexs forward and back as it rotates. Anyone who uses Slow Fly props can easily replicate this. Standard props - its difficult to see because the prop is stiff and flex is miniscule. This causes the vibration and stress on motor shaft / bearings / air frame.
Out of balance of all 4 props to each other, will not itself cause vibration unless any prop itself is unbalanced as an individual. But it causes the Flight Controller to alter power to compensate.

Nigel

 

[lowoctane]

Hey all, it appears that my obsession with balance has lead me to observing quite a variance in total weights of dji stock blades. My latest 4 as follows:
12.075 gram
12.047 "
12.417 "
12.070 "
Of course, I have no way of knowing if my labors provided any real gains on my craft, but plain old physics tells my it has to help, and it eases my brain in this regard. :/

 

[solentlife]

Don't forget that it is not only weight - props work on a combination of factors :

Diameter
Pitch
Weight
Form of blade in how it curves to its pitch
Width of blade
Size of hub

You can have props of significant different weight - but if thrust of the props are same - then Flight Controller will accept as fine.

Nigel

 

[John Locke]

Hey all, it appears that my obsession with balance has lead me to observing quite a variance in total weights of dji stock blades. My latest 4 as follows:
12.075 gram
12.047 "
12.417 "
12.070 "
Of course, I have no way of knowing if my labors provided any real gains on my craft, but plain old physics tells my it has to help, and it eases my brain in this regard. :/

You're worrying too much. Small deviations in prop weight doesn't matter, especially only a half gram. You'll find greater weight deltas if you weigh the 4 corners of the craft, at the motor arms, using identical screw points to weigh. If the props are balanced, you're good. ESC's will adjust to the proper RPM using the IMU to determine the motor power needs. It's good to check the prop balance to prevent potential vibration, but I find less than 10% to need adjustments in balance, and those adjustment are very little.

 

[N017RW]

While the motor outrunners are balanced, I doubt each motor is the same weight as well.

 

[solentlife]

Not only that - but the AC is not centrally balanced - if you were to attach a hook dead centre - you will find it hangs off vertical.

Not only that - but think about when you fit a tracker or other item - where do you fit ? It mounts normally to one side.
My SS3 tag weighs approx 50gr installed ...



Flies fine.

Nigel

 

[lowoctane]

Thank you for the info and positive experiences!