Frustrated 4000 Pro User - Works with one camera....

I have been flying with the 4000 HD with my Gripped 7D and 24-105L lens and It usually takes forever to get it balanced even with the quick release system. Even when its balanced, it still doesnt fly right.
Well, today I decided to test out the glidecam with a Gripped D300s with the 17-55mm Lens and I was able to balance it immediately and fly the system with ease and unbelievable smoothness.
Can anyone help me to figure out what is going on that is causing me to not be able to balance my 7D properly?

I am assuming the D300 is a good bit lighter than the 7D.

The lighter payload doesn't have as much influence over the rig weights so the weights are principally creating the point of ballance. The heavier camera will have greater influence and require the whole combined assembly to require balancing.

If it's a pain add more weights to the rig ballance bar or reduce the weight of the camera.

Thanks. I will try those things. The 7D is pretty heavy with a grip and L lens.

First thing I would do would be to remove the grip since it adds weight and increases the center of gravity unnecessarily.

I just removed the grip and it definitely made a difference. I was always under the impression that adding more weight to the top and bottom would cause the rig to be more stable.

See below. I thought I lost this post, but the second one was better.

You have two factors at play here - static centre of gravity and dynamic centre of gravity.

Static centre of gravity is purely how the system sits when stationary and can be adjusted by moving the camera or weights backwards or forwards relative to the gimbal. While more weight at the bottom will make this much easier it could upset the dynamic Centre of gravity.

Dynamic CoG is relative to the inertia of the top compared to the bottom. If the camera lifts as you move forward and then dips as you slow down the camera has greater inertia than the bottom weights so add more weight at the bottom. If the camera dips as you move forward, remove weight from the bottom.

Adding more weight top and bottom will increase overall stability because the whole system will have greater inertia but needs to be balanced top to bottom as noted above. The base weight will have greater effect on the dynamic CoG because of its greater leverage relative to its greater distance from the gimbal. This is advantageous as it gives more latitude in the weight of different camera lens combinations.

Noting the above, you do need to decide on a length for the post and stick to that as changing the post length with change the dynamic CoG.

John Sims wrote in post #13530939
Dynamic CoG is relative to the inertia of the top compared to the bottom. If the camera lifts as you move forward and then dips as you slow down the camera has greater inertia than the bottom weights so add more weight at the bottom. If the camera dips as you move forward, remove weight from the bottom.

You're talking drop time right? I fly the blackbird stabilizer, same principles. What do you usually aim for time wise on your drop time?

Just looking at it from a point of mechanical theory. From a theoretical point of view, if you can get the dynamic CoG to coincide with the centre of the gimbal the system should remain in equilibrium. The down side is the bottom weight may not have enough influence over the camera to stop it floating away from the vertical.

What do you mean by drop time?

Drop time is when you tilt the rig completely horizontal, how long it takes to re-orient itself in the vertical position.

gibsonla wrote in post #13538547
Drop time is when you tilt the rig completely horizontal, how long it takes to re-orient itself in the vertical position.

Got you. What do you aim for? I would have thought as slow as you dare but trying to avoid so much float that the camera has a mind of its own.

The limitations of the cost/value engineering in the cheaper solutions are always going to be a compromise though I guess.

I find personally that ~2 whole seconds works best for me.

Thanks for all of the replies.
I personally go for a 2.5-3 sec. drop time.
In general, do you all prefer a longer rig with less weights on the bottom or a shorter one with more weights on the bottom?

I have a shorter set up, but that's purely so I have the option to get lower to the ground.

Had that issue too, then went with a 2000 much much better