Can a gyro prevent a pendulum from swinging?

[gulfcoastfella]

I'm trying to build a stabilized platform for a camera. No matter how the base is perturbed (linear or angular), I need the camera to remain pointed along the same vector. I'm assuming that the camera is free to rotate inside a gimbal.

I understand that if the camera's CM is located on the gimbal's axes, then small linear disturbances should have little effect, but the camera will rotate due to even the tiniest rotational distrubances.

I also understand that if the camera's CM is suspended beneath the gimbal's axes, then small rotational disturbances should have little effect, but the camera will swing due to even the tiniest linear disturbances.

So my solution is to place a downward facing gyro at the center of the gimbal's axes, with any remaining camera and other mass balanced at the same point. I believe I only need the one gyro because the pan direction does not require stabilization and will not be part of the gimbal.

Does this sound right?

 

[Curl]

Yeah but I don't know how practical this will be. A small angle is still a small angle, so even a massive gyro will tilt. Plus the mass you're swinging will slow down because of friction, so I don't know how long you need it to last.

Not sure what application this is for, but one thing that works pretty well for cameras is to have one of those foam balls (basically a rubber pouch filled with cotton balls or polystyrene or some soft stuff). Put your heavy camera on that, and any vibration will be absorbed the the soft material since the camera is massive and the material has low "stiffness" if you get what I mean.

 

[gulfcoastfella]

I'll put the problem another way. A pendulum sits at rest, hanging from a pivot which stands on a frictionless surface. Attach a spinning, downward pointing gyroscope to the pendulum. Now, displace the pivot horizontally along the frictionless surface some small distance.

Would the presence of the gyroscope alter the response of the pendulum?

 

[Curl]

Yes, are you familiar with the angular momentum vector?

 

[gulfcoastfella]

Yes, angular momentum for a point mass is

\vec{L} = \vec{r} x \vec{p} ,

and for a solid body, the angular momentum is

\vec{L} = I \vec{\omega} .

I forgot to mention that the gyro axis is fixed along the radial of the pendulum.

 

[Curl]

Okay good. Now you need to understand that to change the angular momentum, a torque is required. The L vector points in the direction of the pendulum stick, if I understand how you have this set up. When pendulum swings, the L direction changes with it (since u said it is rigidly attached). This requires a torque. In a simple pendulum the torque is from gravity (moment of weight about the pivot). So essentially the amplitude of the pendulum swing is reduced if |L| is increased. Why is this so confusing?

 

[rcgldr]

Is there a reason that a conventional home made steadi-cam setup won't work? I assume that the weighted bar at the bottom is setup so linear acceleration doesn't create any torque along the rod connecting the bar below and camera and mount above.

http://www.yb2normal.com/DIYsteadicam.html

 

[AlephZero]

A "passive" system contain a gyro will not stabilize anything well. The reason is simply that unless the gyro moves from its stable position, it can't generate any force or torque. So the gyro can reduce the movement, but never eliminate it completely.

The only way to overcome that is to make the gyro much bigger than whatever it is supposed to stabilize. That is practical for something like a gyrocompass, but not for something like a camera platform, unless you plan to use a gyroscope that is much bigger and heavier than the camera.

The other approach would be make an "active" system useng a (small) gyro as a rotation sensor, to control an independent power source (e.g. an electric motor) that applies a force to the camera platform. But that is getting much more complicated than a conventional (non-gyroscopic) passive steady-cam mount.

 

[Cleonis]

I confirm what alephzero says:
A "passive" gyro is unhelpful for preserving a particular attitude.
In engineering, whenever gyro's are used the system is an active system.

For example, in the past ( I think around 1900) there have been experimental gyrocars. A gyrocar has only two wheels, just like a bicycle. An active system maintains the vertical position.
First I need to define some axes. For two of the them I will use the same names as in aviation:
Roll : rotation along the axis that runs from the gyrocar's front to back,
Pitching for "pushing the nose down" or "lifting up the nose"
And 'swivel' for rotation around a vertical axis.

The gyrowheel was suspended in such a way that its axis was along the vertical, with some freedom for pitching motion.
The gyrocar stayed upright as follows:
Whenever the car tended to roll this was sensed (mechanically) and then a mechanism would pitch the gyrowheel somewhat. The pitching motion of the gyrowheel gave rise to a torque (a gyroscopic effect) that counteracted the tendency to roll.
These gyrocar setups were purely mechanical, no electronics was involved.

(There were also more sophisticated setups. For example, the system may use two counterrotating gyrowheels, so that some undesirable effects cancel out, and only the desirable effects remain.)

Anyway, whenever gyroscopes are employed for stabilization its an active, responsive system.


A steadicam system uses only inertia, that is why it can be a passive setup. But when you introduce a gyrowheel things get very complicated. With a gyrowheel you get gyroscopic effects.

 

[rcgldr]

An active system could also use servo motors and 3d gyro like sensors (these are microchip devices, not spinning wheels), but I'm not sure how much they could smooth out jerky input motions.

 

[gulfcoastfella]

Thanks for all of the replies. I had thought about making an active system using an RC servo set I already have and an Arduino board. I'll see.