Spatial contact force block

Hi

I am trying to build a model for the dog clutch with Simscape multibody as shown in the below figure. each side can rotate independantly, and the dog teeth contact each other. the model is translated from solidworks using Multibody link. To model the contact, I am using the spactial contact force block. I tired to run the model and rotate one dog side but it penetrate the other one.

According to MATLAB help the geomtry export should be turned on and 'export entire geometry' can be seen. However, In my case, I see only the option 'convex Hull'

[Yifeng Tang]

Contact force only works with Convex Hull at this moment. See Documentation page here: https://www.mathworks.com/help/releases/R2021a/physmod/sm/ref/spatialcontactforce.html?s_tid=doc_srchtitle

I also want to point to the Dog Clutch block in Simscape Driveline, maybe it can help with your model: https://www.mathworks.com/help/releases/R2021a/physmod/sdl/ref/dogclutch.html?s_tid=doc_srchtitle

If you want to stay in the Multibody, I think it's possible to separate the teeths as individual solid blocks. This way they'll all be sufficiently described by convex hulls. The model will look messy though.

I'll comment again if I can find a better solution.

[Ayham Aljawabrah]

Hi Yifeng Tang!

Thank you for your comment.

This model is a simplifed version from my original model which contiants teeth with chamfer, and other complicated geometry. I started to look after third party software such as Ansys motion to integrate with my model.

for the dog clutch block, I already checked that, but it assumes that, the tooth is flat, and my model has chamfered tooth. Can the affect of the chamfer be included by somehow, or can I use this block to build my customized one using the Simscape language?

[Yifeng Tang]

Hi Ayham,

Thanks for additional details.

To include chamfers in Multibody contact force modeling should be OK, as the geometry of EACH teeth is probably still a convex hull. However, you still need to treat each teeth individually. How many teeth do you have? If not too many, say 3 or 4, this may worth a try.

Ultimately this will be a trade-off between the pain with modeling individual teeth for contact force v.s. the pain with co-simulation with another software. You may find on this page some information on simulation platform integration: https://www.mathworks.com/help/simulink/co-sim_gateway.html?s_tid=CRUX_lftnav

The dog clutch block in Simscape Driveline is not open-sourced. Some blocks in the Driveline library have the Simscape code exposed, but not this one. I don't think customization based on it would be feasible at this point.

[Ayham Aljawabrah]

In fact, I have dfieerent geometries with teeth number ranging from 5 to 30 teeth, and each of them with 4 differnt chamfer angles.

Many Thanks!

[Yifeng Tang]

Looking at the screenshot, it appears that you are using the import tool from CAD into Multibody. I wonder if it is possible in CAD to separate the teeths from the base so they appear as individual parts in Multibody. You may then do the convex hull thing with each teeth. Try it with a small number of teeth and see how much pain it was before going to all 30 of them.

[Ayham Aljawabrah]

Yes, it can be done if I model the base and teeth as different parts then assamble them into an assembly. You suggested a good procedure to follow. Thanks

[Yifeng Tang]

Just summarize the discussion into the answer.

Have fun with your modeling!

Answer 1

[Yifeng Tang]

Contact force only works with Convex Hull at this moment. See Documentation page here: https://www.mathworks.com/help/releases/R2021a/physmod/sm/ref/spatialcontactforce.html?s_tid=doc_srchtitle

I think it's possible to separate the teeths as individual solid blocks. This way they'll all be sufficiently described by convex hulls. If possible, separate the teeths from the base in CAD so they appear as individual parts in Multibody. You may then do the convex hull thing with each teeth. Try it with a small number of teeth and before going to all 30 of them.