For simulation, you probably want to look into putting your logic into Update() or FixedUpdate() functions and using Time.deltaTime or Time.fixedDeltaTime for computing incremental updates to your objects.
Co-routines could probably work, but what's the reason why you're trying to use coroutines?
Some code would also help identify the problem you're having with coroutines, pseudo code would not help if you're having a specific issue and not seeing your coroutine fire.
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