Hey guys, trying to get a feel of the Mōvi by using my Canon 5D Mark II for now and I'm having a bit of a hard time with the roll balance. I've got the tilt pretty solid, I think. The camera stays in each position no matter if I point the lens down or up. The roll balance I can't seem to get right, though. The camera is centered when the roll axis is centered. However, if I move the roll axis to several locations the camera always seems to want to return to the center position. No matter if I move the roll axis to the left or the right. Camera always seems to gravitate back to central. This is obviously a problem since I cant really slide the assembly to the left or the right to counteract for this since that would throw of balance at the center position. What is the trick here? Is something else affecting me not being able to achieve better roll balance? I made a little movie to help visualize the problem:
When I'm doing it it seems to be based on how off center left to right the load is and micro adjusting the height. First I realign everything observing the fact that the motor on one side is throwing it off (I counterbalanced this by mounting my FF motor to one of the height adjustment rods then re-centering the load). With the left to right weight balanced and the carrier centered - the last step was 1mm micro adjustments to height.
Have you tried it without the HDMI cable attached? Just wondering if that is affecting the roll. Also the micro adjustment to height does have some affect on roll. After doing that you may need a slight re-adjustment to the front/back on the camera plate.
On mine I think the wire mesh surrounding the IMU and tilt motor wires coming out the back are what is wanting to bring the roll back to center. Cheers, Jeff
Yeah it's very strange. I moved the system up on the rods a little bit and now the roll balance seems perfect, staying in place. However now my tilt is off. I'm not sure what the best way to get all these aligned in unison would be. One or the other always seems to be off.
not strange at all. it just takes time and patience. make sure the camera doesnt rotate horizontally left or right on the camera plate when making adjustments...the weight of the lens will throw off roll balance if it's even slightly moved left or right.
Phillipp: If I understand you correctly, the camera's center of gravity is, by definition, below the roll axis -- which is why it is behaving like a pendulum and returning to the center position (as a pendulum does). Try lifting the camera up in height on the front vertical tubes -- until it starts to flop over to left or right -- at that point the C of G is now *above* the roll axis by definition, so very, very gradually lower it and you should be able to find the sweet spot between "flop left/right" and "return to center." Hope this helps. Andy.
I think Jeff is right - the wire mesh from the two cable harnesses applies a slight amount of re-centering force to the roll axis. If you have tilt balanced well, as it seems you do from the video, then the re-centering effect should be very slight. Well within the range of what the roll motor can stabilize. (If tilt vertical balance were way off, you would notice a much more aggressive "pendulum" effect.) Physics time: The wire forces affect the gimbal in a different way than imbalance. If the C.G. is low or high, then side-to-side accelerations will cause a torque on the gimbal just like the force you feel in an accelerating car. If the C.G. is perfect, even if the wires exert centering force, side-to-side accelerations won't create any torque. What will create a slight torque through the wires is rotating the handles around the roll motor. But that's what the roll motor is there to cancel out.
Moving the camera vertical on the tilt tubes always affects tilt, so this would not work. Your roll balance issue is most likely due to the mesh cabling or the HDMI cable or a combo. Try removing the HDMI cable and balancing. With heavier cameras (Epic, Cooke, FF, etc.) all the mass is cantilevered out on those tubes which I believe has a slight affect on the roll balance. Probably not much of a problem in your situation with the MkII. In any case, I've not had a problem with roll being off by the amount you have even with the heavy setups.
Tried it without the HDMI as well. No go. I either get the tilt to balance or the roll but not both at the same time. The pan balance seems really solid. The tilt seems really good. Only if I Point the lens beyond looking up (so it looks backwards basically) does the tilt not hold and the camera lens wants to go towards pointing straight up again. The balance, though, just no go. It always wants to go back towards center. Maybe I'm just making some very basic mistakes that I simply can not see since I have never done anything like this before.
When I said this above - "In any case, I've not had a problem with roll being off by the amount you have even with the heavy setups." - it may have come out wrong, I could've been more clear. With roll out of balance the amount you have, the roll motor wont have a problem compensating. I have had the same issue before.
Hi Philipp, If your tilt vertical balance is good (Which it is in the video you posted!) and your left to right roll balance is good when the camera is roughly level then you are good to go. With a lighter camera like the 5D the tension from the mesh wiring on the roll beam is enough to make it come back to center on it's own like you show in the video. Tabb
Ohhh....I think you're right -- on the MōVI, unless I'm mistaken, the tilt axis of the MōVI is in the same horizontal plane as the roll axis -- the knuckles on the end of the roll beam don't allow you to tilt the side booms upwards, right? So on the MōVI we cannot use the "trick" that we can on the 3-Axis gimbal of getting the camera C of G in line with the tilt axis, and then elevating the front of the side booms to bring the C of G of the camera up into line with roll axis. As you say, therefore, you have to balance tilt to bring the C of G of the camera in line with the tilt axis. And because the tilt axis and the roll axis are in the same horizontal plane when the gimbal is horizontal in tilt and roll, than means the camera C of G is now on that plane, although probably laterally displaced one side or other of the roll axis. To balance in roll you have to move the camera from side to side either using the front transverse booms or sliding the entire roll beam in its mounting. Do you think leading the cables out along the tilt axis would minimize their effect -- there would be torsional forces about the long axis of the cable, but there would not be any forces caused by the flexing of the cables and the wires within? Thanks, Brad. Andy.
I experienced the same problem and came to the realization that the entire roll axis is mounted to the roll motor in a bottom heavy position. As there is no adjustment for that, and since I wanted a separate battery for my camera, focus and iris system, and video transmitter package, I mounted a Freefly lipo battery on the top of the roll beam, just in front of the roll motor with sticky tape to get through my first job. It was slightly top heavy but much closer. Since then, I machined vertical slots in place of the 4 mounting holes that attach the roll beam to the motor and now I can slide the whole system up and down to get perfect balance just as we can already slide it left and right.