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3-Visitor

## Center of Gravity is not changing

So I have only just started working with analyzing center of gravity (CoG) and there is something I can not figure out.

I opened up Mass Properties - I clicked preview - and the CoG was in between the robot's two back wheels. I added two large blocks of iron to the front of the robot and the CoG did not change.

(Here are some images to help explain my problem.)

The CoG is located between the black wheels in the back.

The CoG is still located between the two black wheels. Even with two 12x12 blocks that are assigned the material FE 20.

I have a feeling this is a beginner's mistake.

1 ACCEPTED SOLUTION

Accepted Solutions
24-Ruby II
(To:caccepted)

Hi,

to re-compute mass properties, click File > Prepare > Model Properties > change (in Mass Properties row) > Calculate (in Mass Properties dialog box).

MH

Martin Hanák
5 REPLIES 5
11-Garnet
(To:caccepted)

What's the total mass - is it realistic or is it several ton(ne)s?

If it's higher than you expect, check the individual component masses (click the 'i' icon to open up a larger window with the full information).  Some components may have a default density of 1, which depending on your units could be close to black hole material (in my case it would be one tonne per cubic millimetre!).

I neglected to mention that before I put those on I put two 3"x3"x3" blocks of assigned iron on. It was unchanged then and that led me to go a little over the top.

The weight is very close to what I expected. A 12in. cube of cast iron should weigh around 150lbs. The measure of that cube in PTC Creo 2.0 is a weight of 149lbs with the assigned material being fe40..

24-Ruby II
(To:caccepted)

Hi,

to re-compute mass properties, click File > Prepare > Model Properties > change (in Mass Properties row) > Calculate (in Mass Properties dialog box).

MH

Martin Hanák
3-Visitor
(To:MartinHanak)

That fixed it! Thank you. This goes is my PTC engineering notebook.

1-Newbie
(To:caccepted)

Did re-computing - as Martin suggested - help you getting the CoG where you expect it? (between the blocks I presume)

Gunter

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