Sorry if this sounds too basic but what determines the amperage draw of a small DC motor? I am trying to do a small project with my son that involves a 12V dc motor, waterproofed, that we attach a propeller and run underwater to create thrust. I first used a small boat bilge pump motor that is rated at 1.5 Amps, attached an RC airplane propeller, and placed a switched 12V battery (8 AH UB1260 ) source. The resultant thrust was too little.
I then took the motor out of an old cordless 12V drill, which was the exact physical size of the previous motor (~1.5x3 inches) connected the same propeller and battery source. This created tremendous thrust, heated the 14 gauge wire rapidly and drew over 20Amps (higher than my ammeter registers).
What is the determinant of how much Amp draw there is in two physically similar motors. Is it the number of windings? the gauge?
We are trying to basically create a very small trolling motor with a simple on/off switch and that can create ~10 lbs thrust. The smallest trolling motor(Seyvelor) creates 35 lbs. thrust. What is the best type of motor/ lightweight/ torque combination? I know nothing about brushless DC motors but would they have a use in this project.
Any advice would be greatly appreciated.