Inspire Center of gravity

[jlo]

I suspect that the inspire 1 CG is off, it sims to be quite back heavy I came to this by holing the inspire right above where the the 2 CF rods join in the middle this makes it a bit unstable in manual mode I hope Im wrong

I had a job in a wooded area the canopy above was some what close so I specked to have poor satellite lock the shot call for the craft to go straight up, at about 12 feet I would loos the ground sensor lock, yellow light would come on and the inspire became very hard to control due to some light wind, after several attempts I ended up aborting the shot, to many trees and branches near by

I have and have flown and build many quads and octos where the frame shape is symmetrical, the components are well distributed including the batteries, so in manual mode the craft is more controlable,
on the Inspire I thought to add weigh to the front but is an idea that I don't like too much, since on this craft I don't want to modify anything, perhaps DJI plans a future heavier front camera, another posible solution are the 2 horizontal CF rods this could slide back but DJI has a seal on that probably for prop clearance
any coments

 

[Kilrah]

I suspect that the inspire 1 CG is off, it sims to be quite back heavy I came to this by holing the inspire right above where the the 2 CF rods join in the middle

Thsi is very obviously not where the aircraft's CG is. If you do a straight line between motors it will cross just in front of the battery, and the I1 is perfectly balanced around that.

 

[jlo]

Well its not that "obvious" like you say but ok, I will meashure and give it more though, my logic was to hold it as close that I can to where the two rods meet in the middle, another test is to fly in total manual with no wind see how it handles

 

[Kilrah]

Not even. Response is a question of FC settings. Even with an imbalance it would behave the same, the FC would compensate it.

 

[The Editor]

Well its not that "obvious" like you say but ok, I will meashure and give it more though, my logic was to hold it as close that I can to where the two rods meet in the middle, another test is to fly in total manual with no wind see how it handles

The Inspire doesn't have a manual mode so I'm not sure how you would achieve that.
Additionally, adding any extra weight would be compensated for by the FC as soon as the aircraft was airborne.
You say the Inspire became difficult to control however a COG offset would not in itself cause this since again the FC would be compensating for any weight differential.

 

[jlo]

Ok so I ran some cord across the Inspire fom motor to motor you are right in that the center of gravity is in front of the battery....but that is not where the craft is lifted from the craft is lifted from where the 2 rods meet in the middle and that to me makes it back heavy

 

[Kilrah]

but that is not where the craft is lifted from the craft is lifted from where the 2 rods meet in the middle

That doesn't matter. The aircraft is one single piece, and its center of lift matches its center of gravity just like we want. The fact there is some torque on the joints is irrelevant.

And as said, unless you exceed the lift capability of a motor the static balance of a multicopter has no impact on its flight behavior.

In ATTI with no wind and no control input it will stay in place. If there's wind, well that will push it around and is perfectly normal. If it doesn't stay in place with no wind check IMU calibration.

And yes the sticks are quite sensitive, that's how it's set to be.

 

[jlo]

Correct the FC would conpensate But what I am talking here is in the event that that you have no assistance from the GPS and no assistance from the ground sensor to stay in position
the copter enters in to att mode FC compensates to maintain level flight but an imbalance frame would make the craft drift in space more easily + an imbalance frame makes some motors work harder than others

 

[Kilrah]

an imbalance frame makes some motors work harder than others

Yes

FC compensates to maintain level flight but an imbalance frame would make the craft drift in space more easily

No.

Some motors will work harder to maintain level, but the aircraft will maintain level the same way it would if perfectly balanced.

 

[jlo]

In all of my symmetrical frames the more I place that illusive CG as close to the middle of the craft and as close to where all motor arms meet the better the craft performs all motors work + or - the same even in wind

before this job I did do a IMU calibration

 

[Helnet]

In all of my symmetrical frames the more I place that illusive CG as close to the middle of the craft and as close to where all motor arms meet the better the craft perform all motors work + or - the same even in wind

You're right. Wrong CG= more correction need by the fc and a possibilities to have the toilet bol.

I have an S800 and S1000 and if the cg is wrong it is less precise and we have the toilet bol phenomene.

 

[mdomeny]

i also had the impression its out of CG... i also own a hexa and an octo (not dji) and also keep cautious to have centered gravity checking on all arms to see if its out or not... battery aligment and gopro place, even my DIY crash bowl / hat has to be center do to the circular setup of the hex and octo...
i was wondering why its out and also read that i1 was designed modular for later upgrades so a better / bigger camera would compensate the backheavy body... i also wonder how much more backheavy the i1 is with the bigger 5700mhA battery...

 

[johnmont250]

nice strings, like aligning a formula car. very nice to see the cross mark line up perfectly with the center of the craft, and the t arms. when the arms are in flying mode the role roll center is so low, I think its one of the main reasons its so stable. i guess you could put 4 scales together and check the corner weights.....