Gimbal's

[Kisssys]

I got to drawing a brushless gimbal today and wondered what the penalty would be to not rotate the Gopro around the center of the lense to make balancing it a little easier.

If the camera is rotated 30 degrees about the center of gravity instead of the center of the lense you have a movemnent of about 7mm. I don't think you'd ever notice 7mm with the Gopro lense. Well let's assume you could, if the stab is working it will never ever rotate anyway, level is level no matter if you pivot on the lense center or the center of gravity.

If we mount the Gopro 100mm below the frame inline with the roll servo, and roll 30 degrees. The center of that lens moves off 50mm and up 13.4mm and we ignore that.

Am I missing something, eveyone is so adamant about this but I don't see it.

[13brv3]

I'm with you on this one Steve. The photo purists insist that it's imperative that you have the lens as the center of the rotation, but I think that's a lot like those audiophile types who claim they can hear things that dogs can't... Even if it was significantly off, and you were rotating the camera instead of the copter, I still don't think you could notice.

Time to go hide from those photo guys now
Rusty

[Kisssys]

Hi Rusty,

Well you make me feel better that I'm not the only one who has at least thought it was a little hokey. We'll go hide together somewhere.

[Max]

Did someone say "photo purist" and "GoPro" in the same sentence? Ah, no... never mind then.

Of course, it all depends on the lens specs, the actual offset from lens center, if you're shooting stills or video, the desired product, and how much compensation you're actually needing. And sure, some of it will be subjective, just like audio quality. It's easy to make fun of people who are particular about things you're not, but not everyone perceives things in the same way or with the same attention to detail. For example audio perception can vary widely depending on physiology, age, and training.

So the fact is that there will be some movement if the lens is off center of rotation. Whether you'll notice or not, is indeterminate until you try.

-Max

[joebar.rc]

Nice debate always , but if the gimbal controller is doing its work the camera and lens will never move, at least not in the roll ax. so I never know what the fuzz is about getting the lens dead center in the roll.

Recently I saw a vid from somebody that also want to proof that, he placed the gopro in roll center of the brushless gimbal and two other gopro's 15 cm from center on every side. Recording simultaneously and you really could not see the difference.

For brushless gimbals is placing it in center obviously more easy for getting the balance right.

[JussiH]

For a gopro, the lens do no have to be on the roll centerline. The FOV of the camera is so wide that it does not make a difference to have it off the centerline. In fact that probably goes for most cameras commonly used, since most people are using glass that is =< 26mm. I would say that you need the equivalent of a 50 or 80 mm before it gets even remotely visible.

Also, since the cam in most cases are underslung, the camera sits underneath the roll axis of the craft anyway.

[Max]

In a StaediCam type setup, the camera doesn't move at all if the rig is doing it's job. But with a gimbal like we're discussing, the camera is "always" moving, opposite of the craft movement. Since the gimbal frame is rigidly attached to the craft, the camera has to move to compensate. If the camera was suspended on a pivot, like the Ecilop idea, then it would not be moving along with the craft, and the sensor/axis alignment wouldn't matter at all.

I like using Visio to, well, visualize these kinds of things. It's pretty quick to draw some shapes, group them as needed, and set the rotation centers. Then you can simulate what happens when you rotate 'em.

visio-gimbal.png (27.22 KiB) Viewed 10258 times

gmbl-roll-centered.png (30.21 KiB) Viewed 10257 times

gmbl-roll-offcenter.png (30.48 KiB) Viewed 10257 times

-Max

[Kisssys]

Ok, I thought it was a waste of time, The Staedicam or a Ecilop solves the issue but not practical. If that lense was 200 mm
and kept it level I don't think it would matter either when it's slung so far below the rotation point.

I always draw in Rhino3D and some in Solid Works because it can output files in formats that my CNC machines can use. I always have models of the camera's, servo's, motors etc that I can throw up to use as reference.

[Max]

When I grow up I want to have CNC machines too...

BTW you gotta balance the sh!t out of a Steadicam rig as well. They're quite sensitive. Also I've tried the small/cheap one they sell for GoPro/iPhone, and really wasn't very impressed... more of a gimmick, though maybe with some training and more counterweight it could be mildly useful.

Cheers,
-Max