Check out these links, the first one has some info on the math.
https://www.electrical-contractor.net/ubb/Forum1/HTML/001802.html This next one is just plain fun to see what can be done by someone with a creative mind.
This "Hillbilly" is no idiot.
https://www.electrical-contractor.net/ubb/Forum7/HTML/000234.html It is interesting that the collection of motors running together gives him the power he needs to start the big one.