How to find center of mass of robot?

Hello,

I have been wondering about the different methods of finding the center of mass of a robot? Mine is a balancing robot, so it has two wheels and a chassis on top. I need to find the center of mass so that i can tune the robot to balance. I have done some research but i have only been able to find the following 2 ways:

  1. Use the conventional method of finding the center of mass an irregular object with weighted lines and then the junction of all these lines would give the center of mass. But i don't know how reliable this method is? Since the robot is a 3D object, so its center of mass will lie somewhere at a depth inside the robot chassis?

  2. Design the whole robot, part by part in a CAD software, like Inventor and then use the software's features to let it automatically find the center of mass. Unfortunately, my CAD skills are not good enough.

Any help and suggestions are appreciated. :slight_smile:

You can get a rough idea of where the center of mass of an object is, by balancing it on your finger in several different orientations. The center of mass is always directly above the balance point.

That would be a bit difficult with my robot, since the middle part is mostly empty space so there isn't much to hold onto to put my finger, as there are just 2 plates for the electronics and batteries. Also, i wanted to find a better method so that i can write about it in my project report so it doesn't look amateurish. :slight_smile:

There is nothing amateurish about the method. It is identical in operating principle to the "weighted lines" method. Both are very accurate, if you take proper care in the measurements.

But if you want to appear to be really cool and technically sophisticated, by all means build a CAD model. The center of mass calculated by the program won't be accurate unless you accurately know the masses, shapes and density distributions of every one the parts, but who else would know or care?

DryRun:
That would be a bit difficult with my robot, since the middle part is mostly empty space so there isn't much to hold onto to put my finger, as there are just 2 plates for the electronics and batteries. Also, i wanted to find a better method so that i can write about it in my project report so it doesn't look amateurish. :slight_smile:

Suspend it from strings then.

I wouldn't class Sir Isaac Newton as an amateur.

Post a photo or two, and we may be able to help where to put your finger.

Spin it while in free fall.

Make the batteries and control part able to shift over the wheels like a rider on a bicycle, dynamic balance. Once the wheels spin they will provide gyroscopic stability.

Are the wheels inline or co-axial?