  A digital twin of a direct current brushless (BLDC) electric motor and
propeller is developed for predicting the generated thrust when there is no
motion of the system (static conditions). The model accounts for the back
electromotive force, the propeller drag force, and the finite response time
arising from the electromagnet winding inductance and DC resistance. The model
is compared to a textbook model of BLCD dynamics and to experimental
measurements on a KDE Direct KDE2315XF-885/885 Kv motor with a 945 propeller
and a Holybro electronic speed controller (ESC) driving an AIR 2216/880 Kv
motor with a 1045 propeller. These systems are typically found on Group 1
uncrewed quadcopters (drones). Both the steady-state and transient dynamics
depart substantially from linearized models found in the literature. This study
is a starting point for disentangling the dynamics of the motor and the change
in propeller dynamics due to complex airflow conditions.
