# Self balancing robot - how to find centre of mass?

Hello everyone,

I have been brainstorming on the different ways of finding the centre of mass of my self balancing robot, but i have yet to find a reliable method.

My question: What are the possible ways of finding the exact location of the centre of mass of the entire robot?

Here is what my robot looks like. It has a modular design with each plate holding different components:

Currently, my ideas on how to find the centre of mass:

1. Use a bob suspended on a string and try to figure out the point where it crosses. But this is not really working out as the robot is a 3D object and its centre of mass is somewhere inside the chassis.

2. Use CAD design software to find it. I don't know where to begin...

3. Some maths formula to find centre of mass of each plate and then somehow join it all together to get the final answer of the location of the centre of mass?? I read about this during my search but i could not find any specific method or any formula.

4. ??

1. Let the robot figure it out by itself.

You don't need the robot to know where exactly the centre of mass is. You just need the robot to balance.

wvmarle:
4. Let the robot figure it out by itself.

You don't need the robot to know where exactly the centre of mass is. You just need the robot to balance.

Actually, i do. It is part of my project. I need to do the modelling and i need to find the robot parameters.

Any help is much appreciated.

If you have to know the center of mass, your model probably will never work. Redesign it for not using the center of mass. Afterwards, if everything works, you can think again about determination of the center of mass from the other (then known) parameters.

Suspend the robot from a single light cord attached to the robot.
The centre of mass will be directly below the suspension point.

Repeat for several different suspension points, taking photographs of the results.
On each photograph draw a line to extend the cord through the centre of mass.

The centre of mass is where each line intersects.

If the robot has symmetry in one particular axis, then the centre of mass will be on the centre line for that axis

You should break the robot down into component parts, determine the mass of the component (weigh it) then determine the location of the component's centre of mass. You can then use those to calculate the centre of mass of the complete robot.

Remember that the centre of mass need not be on the object. The centre of mass of a wheel will be in the centre of the axis of rotation.

Here is a 2D example, you can just extend it to 3D. It also demonstrates using a plumbline but that method is not suitable for a robot.