April 2022 Propwash Web

This is an explanation of how to do it. Take a drill and spin the motor. The meter reads frequency so to get rpm multiply the 56.9 times 120 and divide it by the number of poles the motor has. This is a 6-pole motor so the rpm is 1132. Next measure the AC voltage across the leads. This gives .481 volts. The kV is the rpm divided by the voltage and a constant (1.3433). This gives a kV of 1752 compared to the motor rating of 1800 kV; close enough The readings across the other windings should be close if all the windings are good. Loss of kV could mean that the rotor has become demagnetized if the windings test with equal resistance. Now that you know all this about your motor, how can you change things? Souping up an electric motor of a given size is usually done by rewinding the stator. That will be covered in the next article. For more explanation on these measurements along with great videos see https://www.radiocontrolinfo.com/ brushless-motor-efficiency/ In Memory of … Rodger Reed By Greg Reed NAMBA District 19 Boater Brushless Motor Theory (Continued from page 27) kV Measurement The kV determines the rpm of a motor for a given input voltage. It is usually measured in thousands of rpm per volt. The kV number is how fast the motor will turn with a one-volt input. To find the unloaded rpm multiply that number by the battery voltage. Actually, measuring the kV isn’t difficult and is a good check on motor condition. The NAMBA Rule Book has a section on how to measure kV: The following formula will be used to determine a brushless motor kV output: kV = (120f/p)/(1.343V) Variable definitions: f = frequency of the motor, as measured in hertz (Hz) p = number of poles in the motor V = voltage measured across the motor as measured in volts (V) PROPWASH 28 April 2022 Motor frequency Motor AC voltage Rodger Reed was a District 19 model boater residing in Parker, Arizona and a member of the Lake Havasu Model Boat Club. Being so close to the Colorado River big boats was his love along with tinkering with various RC projects. With his likeness to real full sized boats, radio controlled Crackerbox was his favorite at District 19 races. Then came along his brother Greg Reed who resides in Lake Havasu City, Arizona who had an affinity of nostalgia towards the 50’s generation of round nosed unlimited hydroplanes. Not to be forgotten, a third brother in the Reed family, Chris Reed supported Greg in his round nosed endeavor of RC old style round nosed stock motor thunderboats which we now know as the Classic Thunderboat class. Rodger however was a thinker outside the box. While the Classic Thunderboat rules were still being ironed out, Rodger would take is expertise as a retired machinist and come up with a different look. He designed the old style shallow picklefork thunderboat. It was a beautiful boat that emulated the look of the old stye full sized thunderboats. Although Rodger’s hull did not make it in the final rules package for Classic Thunderboat, it was his thinking and design work that helped the class grow. Rodger will be missed.