# How do I fix a script for determining chassis stiffness of a Formula Student car?

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Ewan McBride on 4 Mar 2016
Answered: Christoph Hahn on 14 Apr 2016
I have watched this video about determining chassis stiffness and am trying to implement this for my formula student team. I have managed to import the geometry correctly and create my chassis, however when I try to apply my loads the results do not give any answers and do not produce a deformed image of the chassis on the graph. I have tried changing the loads and tried increasing/decreasing the forced but it is not seeming to make any difference.
I have copied what has been done in the video and the simplified frame works fine for me. The matrix I've used for my forces is very similar to the one implemented in the video and the one given from the online download. I've used -1,0,0,0 for any free nodes 3,1,1,1 for any fully constrained nodes and -1,0,0,LOADZ for my loaded nodes (one positive one negative). I have tried variations including changing -ve signs and loading different Axis and trying 1,0,0,LOADZ or 2,0,LOADY,LOADZ etc. but nothing is working. The script is running fine with no errors however the solutions are all "Nan" and the plotted graph gives my un-deformed chassis but no solid line for a deformed state.
Does anyone know how to help with this problem?
I have attached my script for reference and the formula needed to solve
Walter Roberson on 4 Mar 2016
We work better with actual code.
To be honest, it is too much bother to have to go watch a video and track down code for it and then make guesses about how you did your implementation and what might have gone wrong. If you post your code then we do not have to go to that trouble.

Christoph Hahn on 7 Mar 2016
Hi Ewan,
this is the FileExchange entry that I used for the example in the video. The documentation in the code is pretty good. I would start from there and build the model gradually (all examples are running nicely).
Let me note that matrices may be singular and you always have some constraints resulting from the numerics behind. An example that comes to my mind is that you constrain certain a node and apply a high load at the node next to it. Back to the times of my master studies that book was great in explaining the theory of beam theory and its limitations: The Finite Element Method. Zienkiewicz / Taylor
Cheers Christoph

Christoph Hahn on 14 Apr 2016
Let me comment on a question that I get quite often related to that subject:
Truss elements only handle axial deformation. What about bending?
A truss element is nothing but a coil spring. It can only handle tension and compression. You will agree that this is quite a simplification as in reality also other deformation modes may occur such as bending. In order to capture bending properly you have to go for beam elements. There are two pretty popular approaches to account for bending, Bernoulli and Timoshenko beams. Doing some research in the web or in good books will reveal the differences. Short explanation: Timoshenko beams can also capture transverse shear and will give results that are closer to reality, Bernoulli beams are more simplified.