I have a dilemma with the design of a device I want to build which is acquiring the correct size motor (shape & power) in my price range (even finding one within specs). I have found that the motors from cordless drills are ideal for this application (due to size, price and availability) so they meet all my requirements as long as I can use multiple motors to turn one shaft. I need 3-6 motors to drive the axle of a water pump. I can easily fit 6-8 in my design if I need the power and battery capacity is not a concern at all. If I use multiple motors I will use all the same models so they are identical. If multiple motors are used, let's say 18v brushless DC, can I run them in series (would there be any benefit to this)? I can make the battery bank 18-20v or multiples there-of. I can easily run a heavy bus bar if running in parallel so current isn't an issue here. Is one better than the other?