I have been using a variable speed drive for every pump for our machines and had the idea of using 1 drive to alternate between 3 pumps, the other 2 would run start-stop from contactors if demand increased. I've asked drive manufacturers about doing this and they keep telling me there's no easy way to do it (I'm assume they're telling me this to sell more drives). thinking I would have to use single drive, starter for each pump and interlock relays to prevent the starter and drive from powering the motor at he same time and also to switch the drive power to each motor. Any other things I should watch out for?