Why is the COG (center of gravity) way off on the Mavic?!

[AlanTheBeast]

The wobbling while decending fast is known as "Vortex". The props are going through their own downwash as it decends. All quads/drones will do this decending vertically straight downward fast. The "simple solution" is to fly forward while decending,making the props clear their own downwash.Racing drones are really bad about this,as there is no stabilization in acro. Just fly forward while decending( it dosen't take a lot of forward stick),and see how smoothly it will come down. If you must decend straight down,do it slowly.

I don't think it's an issue needing prevention. The wobbling is a product of the drone inherently dealing with the VRS RVS. ie: a rotor loses lift because of VRS RVS that causes the drone to bank towards that rotor which helps break the VRS RVS and/or the RPM is adjusted and that breaks the RVS ... then another rotor goes through the same thing and so on. If all 4 rotors went into VRS RVS simultaneously and RPM changes could not deal with it, then it would be a different kettle of fish.

It's also possible the control laws of the drone recognize the condition and purposely deal with it creating the wobble.

 

[AlanTheBeast]

Cheers, must say I like the visual balance of the mavic with the rotors, don't know why, just do, it seems purposeful!

I would like to think the designers must have some awareness/knowledge of aerodynamics and how it all works and isn't just because it folds up better that way!

On a quad there is no need for rotors to be tilted this much and the consequent power imbalance in most flight regimes. It results in system compromise but they made up for that with a nice fat battery to keep the endurance up.

Look at how snugly the blades fold to the body. That is the whole story.

 

[Kilrah]

What i am trying to say here, is that i see 4 identical motors, and seeing all sorts of asymmetric design points, there must be situations that a combination of factors will led to a motor that will not be able to respond (under-powered) to the controller set-point, ...

The operational parameters and limits are set so that this never happens. And if you say it can happen, then it can happen with any design even when perfectly symmetrical. Really it barely changes a thing.

 

[mavic6611]

Maximum negative throttle on decent is asking for trouble with or without the perfect CG

 

[adamsweeting]

The mavic was designed to fly forwards, and pack down small.
Even my perfectly balanced hand built quad wobbles on descent - as others have said, prop wash.

 

[Slayerstwin]

Camera weight?

 

[AnzacJack]

The aspect not mentioned is dynamic and static stability. This is largely set by the dihedral design of the rotor disks. Plus there is always the bit of form over function

 

[2X25MPG]

If you lift the Mavic with the two diagonal opposite motors (on the propellers hub), the Mavic will lean heavily forward ("nose heavy").

This "mechanical" design imbalance is strange ... , and as a consequence, provokes a problem that can be seen when you decent the Mavic vertically down at max speed (full throttle low), ... the controller/motors can't keep the Mavic level and a noisy wobbling appears very clearly!

The only reason i see they made this compromise, is the folding design restrictions and the free field of view for the camera (no propellers)

Sad imo...

Slowdown your rate of decent.... no more wobbles ! I had the same issue at max decent.... figure it must be instability caused by craft decending through its own prop wash.

 

[dxtrty]

So, in case of emergency, is the fastest/safest way down; left stick fulldown in comb. with a slight hor. move?
or is a left stick fulldown/full yaw an option , maybe with a slight rudder in same direction of the yaw to make the spiral bigger ?

reminds me of the Steep Spirals i did while paragliding....coming out was the trickiest... (keeping the cloth in shape)
probably also with a quad... coming out in style.

 

[AlanTheBeast]

Whether you add yaw or lateral movement probably doesn't accelerate it - but sure looks cool with the full yaw. The "wobble" from RVS VRS doesn't harm anything.

If I had some time to spend on it I'd look at the recorded dh/dt to see if there is a "fastest of them all" descent. Hmm, I'll be out this evening checking out a spot, if I feel extra bored I'll give it a shot.

 

[Ron_Dog]

So, in case of emergency, is the fastest/safest way down; left stick fulldown in comb. with a slight hor. move?
or is a left stick fulldown/full yaw an option , maybe with a slight rudder in same direction of the yaw to make the spiral bigger ?

reminds me of the Steep Spirals i did while paragliding....coming out was the trickiest... (keeping the cloth in shape)
probably also with a quad... coming out in style.

Just add right stick (forward) and move as you decend,and yes you can also add yaw and do it in a spiral. When I come in for a landing I lower the throttle while holding forward stick,comming in much like a plane would do for a landing,and on a day where the wind is really blowing,it will come down,with less pitch,or bouncing around.

 

[Kilrah]

Forward movement (even little) will avoid the wobbles but won't accelerate descent since vertical speed is predefined in the FC parameters. The Mavic is configured for full down stick to command a 3m/s descent.

 

[AlanTheBeast]

Forward movement (even little) will avoid the wobbles but won't accelerate descent since vertical speed is predefined in the FC parameters. The Mavic is configured for full down stick to command a 3m/s descent.

Agreed'd - but always looking for the exception.

 

[Kilrah]

No point, the whole mode of operation is to do everything it can to match that set speed, no more and no less.
Only way to get more is to change the settings.

 

[ThorDar]

It's prop wash. My Solo's do the same thing.

 

[Ron_Dog]

Forward movement (even little) will avoid the wobbles but won't accelerate descent since vertical speed is predefined in the FC parameters. The Mavic is configured for full down stick to command a 3m/s descent.

That is correct! It also makes doing the manuver easier than ever! Plus it looks way better decending in flight,as compared to the "elevator" drop,or as my friend calls it the "yoyo" manuver.

 

[frankbiganski]

Interesting old post that comes into play when renewing one's GVC certificate in the UK in 2023. The new renewal form on the CAA website actually asks for the Centre of Gravity (CG) of my Mavic Air 2 drone, which is not mentioned in its user manual.

Holding the Mavic Air 2 by the front two props, the CG appears slightly below the prop line by maybe just 1 degree?

It's almost nil but still, the CAA is asking some pretty technical questions from this simple property photographer.