You know things get complicated when lots of weird terms start flying around...

We need only three, and these aren't so weird.


This is the second post in "esk8 Structures" series, make sure to read the first one here.

1. Loads – it's what your part/structure gets from the outside. They have nothing to do with the shape/size/material of the part/structure.

Loads can be forces or moments (forces times distance).


For example - you're standing on the board - the load is your weight on the board.

Or - while the motor is working, it tensions the belt which in turn loads the motor mount.

The belt bends the motor mount

2. Stresses – when something is loaded, it becomes stressed. The stresses are internal, and you usually can't see them. Stresses have nothing to do with the material of the part, but they depend on the shape/size of the part.

Stresses are forces divided by area.


The best way to show these is with a movie, look at the colors (and the little arrow which is the load):

Higher loads mean higher stresses, this is clear.

But, how high can we go?


Just slightly below the failure stress.


3. Failure stress - the highest stress level which the material can handle.


While you usually can’t control the external loads, you can choose the material and design the parts geometry to have certain stresses.

And, if it's below the failure level, you have a part that you can live with.


And one diagram to show it all:

Simple diagram do describe all three terms

So, here's the big picture:

Once the loads are known, you can design the part to have the stress level which is safe for the material.


The biggest shift will be from:

"Print it and see what happens"


"Design it and use it as you want"


Honestly, this is my goal with these posts.




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I’m doing something new here.

A short series of posts dedicated to designing your own, as strong as you want, structures.

I’ll cover the basics, so you can do the rest.

Let me know what you think: