As I said here, generally speaking tags are created as questions which require them are created.
The poster of that similar question said in a comment
If there is a tag, definitely there will be a lot of questions.
Yet almost 2 years later there are only 3 questions with the data-association tag, which lends weight to my reply of
It doesn't work like that ..., having a tag doesn't create the questions which require it. Having questions which require a tag causes the tag to be created.
For now though, if you link to some questions which would benefit from the tag, I would be happy to create it. Even better, if you suggest a suitable tag wiki, explaining what it is for, we can ensure that tagging is consistent across questions. As it is, I'm not sure quite what you mean by 'soft' robotics.
Eventually though, you will have enough reputation to gain the tag creation privilege and then you will be able to create tags simply by adding the new tag to a question you have written.
I noticed a question from 2015 which would benefit from the soft-robotics tag, so I have created it.