How do I apply an external force along a World frame axis in MATLAB Simscape Multibody?

I want to apply an external force to an assembly I have imported from Solidworks into MATLAB Simscape Multibody. The assembly was imported using the MATLAB Simscape Multibody Link plug-in. The External Forces and Torques block in Simscape Multibody only gives me the options of choosing which component of force (Fx,Fy or Fz) I want to apply and the frame used for the resolution. According to the MATLAB documentation, this force will be applied at the origin of the attached frame along the selected direction (F x/y/z) of the resolution frame.

My objective is to apply a force along the x axis of the World frame at the origin of the attached frame. However, when I make the appropriate selections in the External Forces and Torques block, the force doesn't seem to be applied as I thought it would be. Am I interpreting the options wrong?

Also, is there any way of visualizing the applied force(s) in the animation (Mechanics Explorer)? It would make it so much easier to see how exactly the force is being applied and along which direction.

[Swarooph]

You can set the resolution frame to 'World' and then say along X axis. The documentation says this will 'Resolve each force component in the World frame of the model.' Did you say you tried this? (Sorry I am a little confused by the question otherwise). If you did try, tell us what did you expect and what is happening.

One way to view the the applied forces would be to 'select' the 'External Force and Torque' block to look at the frame orientations. Since the force is dynamic and can be in 3D it shows only the possible 3D. So give us pictures and tell us what it is that you think is wrong so that it will be easier for us to debug.

[Davide Basso]

I'm having the same exact problem. Were you able to solve it in the end?

Answer 1

[Steve Miller]

The External Force and Torque block allows you to do exactly what you described. It can apply forces/torques to a point on a body along/about the X, Y, and Z axes of the World Frame.

Post your model if you want someone to look at it.

--Steve

[Michael McGeehan]

Hi Steve,

Thanks for the reply. Is it possible to use a dynamic location for the point of force application (i.e center of pressure)? For example, apply ground reaction forces resolved in the world frame to the feet of a walking robot model?

Thanks!

[Steve Miller]

The External Force and Torque block applies forces and or moments to the frame where the block is attached.

To vary the dynamic location for the point of force application you can:

1. Use a Joint to vary the location of the frame where the force is applied
2. Leave the frame at a single location, but vary the moment and force that are applied according to the relative position of the desired point of application and the location of the frame.

--Steve

[Steve Miller]

Hi - look at Joint6. Your input q is an angular input, which is being set to a constant of 0. That input specifies the angle of the joint. No matter how much torque you apply, that part will not spin. You need to configure Joint6 so that it does not have a motion input. Also make sure that your reference frame is not along the axis of Joint6, otherwise the forces you are applying will not have any effect.

--Steve

[Tengfei Niu]

Thank you for your answer，Steve.I set the angle of each joint to 0 or other angles in order to fix the robot in this pose. The external force I applied was at the new coordinate system at the end of Link 6. The purpose was to obtain the deformation of the robot in an attitude where the external force was applied at the end. I think this belongs to static stress analysis. I don't know what is wrong with my approach. If I don't add a joint angle to each joint, the entire robot will oscillate all the time.

[Niraj Dalal]

external force and torque gives instantaneous force ?

Answer 2

[zafrie haziq]

hi steve, how i want to rotate the shaft ? is it using external and internal blog?

[zafrie zainudin]

i meant, external force and torque blog