"To get good results" may be a dangling modifier in this sentence. It depends whether it refers to the model, or something stated previously.
You can use this model in various experiments, but to get good results (from the experiments), the model should be tuned carefully.
This model can be applied to any number of experimental conditions, but to get good results (from the model) it must be tuned carefully.
Either way, this seems only marginally related to using the passive voice. The implied subject is "the person doing the tuning" (or just "you"), but that's not what "good results" refers to. The model isn't getting results from the researcher, after all.
The person setting up the experiment must tune the model carefully, to get good results (from the experiment/model).
Here's a better example:
To get a good night's sleep, your mattress should be selected to be firm but comfortable.
Here "to get a good night's sleep" is definitely a dangling modifier, as it's not the mattress that is getting the sleep, but rather the implied subject "you". The non-dangling version, in the active voice:
To get a good night's sleep, you should select your mattress to be firm but comfortable.