Balancing the Rhino Steady (EZ Steady) Camera Stabilizer
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Have you backed any projects on Kickstarter? I have backed just one, the EZ-Steady, later renamed to Rhino Steady.
This contraption is a camera stabilizer. It helps you shoot professional looking videos where the camera appears to smoothly fly around the scene. It is based on the same principles used by the Steadicam, only smaller and a few orders of magnitude cheaper.
The idea is simple. If you walk around with the camera in your hand you can't avoid transferring some of your own body motions to the camera. This class of stabilizers separates the camera from the hand that holds it with the use of a gimbal. To ensure that the camera stays upright all the time a set of weights are attached around the frame of the stabilizer, strategically positioned to create a balance. When the camera is perfectly balanced you can freely walk or even run around grabbing the stabilizer by the handle, and the camera will be practically fixed on the three rotation axis, unaware of what's happening on the other side of the gimbal. Note that the left to right orientation can be easily controlled, and the tilting up and down can be done by grabbing the bottom of the stabilizer's frame with the other hand, though this comes at the expense of some lost stability.
Unfortunately balancing a camera stabilizer is not an easy task. The Rhino Steady web site claims you can balance it in 10 minutes, and that is, in my opinion, not true.
The problem comes from the fact that there are too many variables that affect the balance, and when you adjust one of them the others need to be readjusted. The process of balancing is then iterative, you start by making big adjustments, and as the balance is improving you have to make smaller and smaller changes. If you have the patience and the time, you will eventually obtain a decent balance and if by that time there is still light outside you can then go out and shoot.
Rhino Steady balancing variables
Here is a summary of all the things you can change to affect the balance of the Rhino Steady:
Camera left/right position. This one is pretty easy to understand, the camera needs to be attached to the stabilizer in a way that distributes its weight evenly to the left and to the right, so that it is left-to-right leveled. This balance is actually not that hard to obtain because it is relatively independent from the rest, you just move the camera left or right on the stage until balance is achieved, and you can check the level in the back of the stage to know when you get there. For very small adjustments you can also slide a little weight in the back of the stage left or right as necessary.
Camera forward/backward position. This is the same as left and right, but in the other direction. The weight of the camera needs to be distributed so that there is no tilting up or down. The camera stage has five different channels to choose from. Note that each time an adjustment is made here you lose your left to right balance.
Bottom weights position. The bottom weights can be attached to three different locations in the stabilizer's frame.
Bottom weight amount. The stabilizer comes with a selection of weights, some thin and some thick. A thick weight is equivalent to five thin weights.
Front weight amount. Like at the bottom, the front of the stabilizer can have different weight configurations. The weights for the front are smaller, but also come in thin and thick formats.
Bottom weights up/down position. The weights are mounted on a screw, so turning the screw sends the weights up or down, and that can influence the balance when adding or removing weights does not help anymore.
Front weights forward/backward position. Like the bottom weights, the front weights can be moved closer or farther away from the frame to affect the balance in a more subtle way.
The definition of balance
A strict definition of balance would be to say that the mass above and below the gimbal should be equal. We also want the mass left and right of the gimbal, from any point of view to be also equal.
We can simplify the above by saying that the center of gravity of the whole system must be at the gimbal.
That sounds good, but unfortunately that is not what we want. If the system is balanced at the gimbal that means that you can put the camera in any position and it will stay there, balanced by the counterweights. For example, you could put the camera upside down at the bottom or all the way to the left, and in both cases there will be no acting forces to bring it back to the upright position.
This is really inconvenient, because achieving 100% perfect balance is practically impossible. If you fly the camera in this mode the small imbalances that exist in the system will over time make the camera drift to some unwanted orientation.
Instead, what we want is to have the bottom slightly heavier than the top, so that there is a small force that brings the camera to the correct position when it drifts off a little. This is equivalent to saying that we want the center of gravity of the whole system a bit below the gimbal.
Now this is tricky, because if the center of gravity is too low, then the system will behave like a pendulum and will be constantly swaying in every direction trying to bring the camera to the upright position but missing and going in the other direction because it is applying too much force. So we want the center of gravity just a tiny bit below the gimbal.
If you think about this carefully, you'll realize that we are really trying to balance the system in two different ways. First, we need to achieve a balance that puts the camera in the upright position when the system is not moving. This is called static balance. We also need to balance the center of gravity of the system so that when we move around the camera stays upright or quickly corrects to the upright position if it drifts away. This is called dynamic balance.
The test for static balance is simple. Just grab the stabilizer by the handle and let its body find the position where it rests in balance. If the camera ends up perfectly upright, then you have achieved static balance. If not, then you have to apply a correction, either by moving the camera in the stage, or by adding or removing weights in the bottom or the front of the stabilizer frame.
The test for dynamic balance is more complex. The method this and other stabilizers in this class use is called the drop test. You grab the stabilizer from the handle with one hand and with the other hand you bring it to a horizontal position. Like this:
Then you let go of the bottom and check the time it takes for the camera to reach the upright position, if it does at all. The outcome of the drop test tells you what to do to improve the dynamic balance:
If the bottom of the stabilizer drops very quickly then the bottom is too heavy. Your only option is to remove weight to make the bottom lighter.
If the system remains balanced in the horizontal position, or if the camera drops to the bottom, then the bottom of the stabilizer needs more weight. In this case you don't even have static balance.
If the system moves slowly towards the upright position, then you are where you want to be. How slowly is a matter of preference, but one to three seconds until the system passes the vertical position seems to be the generally accepted drop time for a well balanced system.
Unfortunately you can't work on the static and dynamic balancing separately, they are strongly linked and adjustments made to improve one of them will always have an effect on the other.
I think that is enough theory to take in in one session. While I would definitely not call myself an expert in camera stabilizers or even less in Rhino Steady balancing, I have spent a lot of time balancing different types of cameras on this device, so in the near future I will be posting a few practical examples, with pictures and step by step instructions that show my reasoning and my decisions. For the first one I will be showing how I balanced my Canon 60D DSLR, so stay tuned for the next article in the series!