April 14, 2022
A simplified DJI RS2 Pro Combo with a BlackMagic Pocket Cinema Camera 4K (BMPCC4k) or 6K rig. To reduce vibrations ensure the gimbal is statically balanced and try to minimize dynamic unbalance by bringing accessories closer to the centre of mass of your rig.
Hi, in the previous video I posted on a Black Magic PocketCinema Camera 4K rig mounted on a DJI RS 2, I showed that I had some issueswith vibrations.
In one of the comments, Australian Image said “the camera isso badly arranged that you are going to get vibrations no matter what”.
And he was right. All those loose cables and especially thatfocus gear, which I should have cut, were probably moving around when I walked.These movements caused changes in the centre of gravity of the rig mounted onthe gimbal.
If the centre of gravity moves around it will staticallyunbalance the gimbal, meaning that motors will struggle and the gimbal willvibrate.
To see this you just need to move a cable from one positionto another position. You just need a tiny change to statically unbalance thegimbal.
Another thing Australian image mentioned is dynamicunbalance. Dynamic unbalance is the result of a non-symmetrical massdistribution, which can be quantified with the Product of Inertia or POI.
The POI is equal to the product between extra mass, radialoffset from the centreline, axial offset from the centre of gravity, and two.
Take this cylinder for example, the centre of gravity is inthe middle. There are no extra weights so POI is zero. If we spin the cylinderabout its vertical axis, it will spin without problems, without vibrations.
If I add two equal masses in this way the centre of gravitywon’t change and the cylinder is still statically balanced. Now POI is non zero.If we spin the cylinder about the vertical axis, centrifugal forces will actthrough the two weights to produce a couple. So basically the spinning cylinderwill wobble and vibrate.
This is something you can test on a glide cam, but on agimbal it’s much more difficult. So as a rule of thumb what you can do toreduce dynamic unbalance is to minimize the product of inertia. You can do thatby bringing the extra masses, which in this case are the power bank and theCFAST card adapter, closer to the centre of mass of the camera.
So, in summary make sure cables don’t move around when youmove the gimbal to keep static balance and make sure accessories are as closeas possible to the camera.
With this configuration I got less vibrations than what Ihad before. As you can see in the following tests some vibrations are stillthere.
This is what I got with the standard mode. I was activetracking this target.
This is what I got after turning supersmooth on.
Here I changed lens. I replaced the 45mm lens with a 16mmlens.
I tried selfie mode, but walking with 3.5Kg on an extendedarm is really heavy.