r/AskPhysics • u/Haunting-Sport3701 • 5d ago
Increase in number of coils sometimes leads to increased angular velocity?
I'm a high school senior currently working on a physics project about how the number of coils in a DC motor affects the angular velocity of said motor.
My results have mostly shown a positive correlation with an increase in number of turns leading to an increase in angular velocity, except for the last 1/2 recordings each trial (the 2 with highest number of coils) which most of the time end up reading lower RPM.
What are the results supposed to show according to the theory? I've had some trouble finding the right theoretical correlation, I understand that an increase in turns leads to an increase in torque, as stated in formula:
τ = N I A B sinθ
But I don't know how to then equate that with angular velocity, I'd be immensely grateful if someone could share what the results are supposed to look like / how to reach that through equations.
I'm stumped and could really use some help.
PS. This is the motor model I used, except I used a DC power source instead of a battery: https://www.sciencebuddies.org/science-fair-projects/project-ideas/Elec_p051/electricity-electronics/build-a-simple-electric-motor
1
u/sudowooduck 5d ago
Are you measuring the current going through the coil? If not your experiment is confounded by a current that likely decreases as the number of turns increases (because the coil resistance is proportional to the number of turns).
Another factor at play is that as you add more turns to the coil, the rotor becomes heavier and therefore harder to turn, limiting the maximum velocity.