CG of Bins

[John Larock]

Hey, has anyone modelled and calculated or measured the specific CG (Center of Gravity) of the Sterilite Bins? Looking for height of CG from the bottom of the bin.

Thanks in advance.

[Jim Meyer]

The easiest way I know to do this is to ballance the bins on 2 different edges. The CG, when ballanced, will be directly above the ballance point. Doing this on two edges will give you two lines that intersect at the CG.

I don't have a bin handy, but it shouldn't take long to do this.

[Gui Cavalcanti]

One thing I've tried before is to attach 3 strings to the outside edges of the object you are weighing. Keep adjusting the lengths of the string until all 3 have been pulled taut, and hang a weight from the point at which they meet. There's the center of gravity for that plane.

I've only seen it done once, and it was a tedious effort. Does anyone else know of a better method? Namely for 130 pound robots.

[srjjs]

First, find a function to express the density of the box. The x-coordinate of the center is given by dividing the integral of x times the function by the integral of the function. The y-coordinate is the integral of 1/2 the function squared divided by the integral of the function.

[Brandon Martus]

Originally posted by Gui Cavalcanti
One thing I've tried before is to attach 3 strings to the outside edges of the object you are weighing. Keep adjusting the lengths of the string until all 3 have been pulled taut, and hang a weight from the point at which they meet. There's the center of gravity for that plane

That sounds very similar to the experiment we did in my one and only college physics lab.

[Jim Meyer]

Originally posted by Gui Cavalcanti
Does anyone else know of a better method? Namely for 130 pound robots.

My favorite is as I described for the crates. Balancing your robot on three sides. Put some masking tape on the robot vertically above each balance point. Each of these represent a plane in which the CG lies. The intersection of these 3 planes is a single point.

You can also do this by sliding pipes under your robot, starting from the edges and moving them to the center. The pipe with the least force always moves the easiest and you always end with the pipes under the CG of the robot.

A method used for cars is to suspend your robot and swing it like a pendulum. The period of the pendulum can be used to calculate the CG.

Another method used for cars is to put scales under all four wheels and then elevate the front and measure the weight transfer to the rear, and vice versa.