What's wrong with the planar joint of the test platform in my formula student vehicle suspension model?

Question

Shuo Wang 2016-7-28

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https://ww2.mathworks.cn/matlabcentral/answers/297593-what-s-wrong-with-the-planar-joint-of-the-test-platform-in-my-formula-student-vehicle-suspension-mod

编辑： Shuo Wang 2016-7-30

final model_v1.zip

Dear sir It's me again, I reset the base frame and follower frame again, but it still doesn't work. The model report is shown below, it seems the planar joint setting is still not right. I think my setting should be right, because I set the X axis pointing up, Y axis pointing to the right and the Z axis pointing into the screen in RIGHT VIEW. However, it is still not right. I delete the other three suspension assemblies and only leave the rear left suspension with the paltform. I'll upload the files and hope you can have a look. Thanks again for you precious time.

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Answer 1

Swarooph 2016-7-29

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https://ww2.mathworks.cn/matlabcentral/answers/297593-what-s-wrong-with-the-planar-joint-of-the-test-platform-in-my-formula-student-vehicle-suspension-mod#answer_230208

Hello Shuo,

First things first. You are making great progress! Congrats!

Next, let me show you the best way to debug. In our case the planar joint seems to be the issue. So let's first delete its connection to the rest of the assembly. So disconnect the line between Wheel/F2 and Planar Joint/F. Now update the model. You see that it does not error out. This is good! Because Now we just need to align Wheel/F2 and Planar Joint/F appropriately.

Wheel/F2 and Planar Joint/F need to be at the same 'Z' location. They can have some leeway in X and Y directions. Why is this? Because using a planar joint we are going to allow translation between X and Y. However ONLY revolute is allowed in Z. This means any discrepancy in Z position between Wheel/F2 and Planar Joint/F will result in an error. Let's take a look at this graphically to see if this is the issue. To do this, let's use the mechanics explorer.

ISO VIEW

FRONT VIEW

You can see that the frames are translating a little in the Z direction. This cannot happen since Z can only allow revolute motion.. You need to take a look at your translation blocks and figure out how to align Wheel/F2 and Planar Joint/F. You need to look at the various dimensions specified to get to this translation.

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Shuo Wang 2016-7-30

编辑：Shuo Wang 2016-7-30

Thank you Mr Swarooph, from your answer I finally find out that a planar joint is not available for my model, because the wheel will not only move in X and Y axis, but also move in Z axis. Hence, a 6-DOF joint should be the right choice.

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