Use a 2 Ohm load with <0.1 Ohm switch and a keep motor on while switching another R of 1.33 ohms including FET on/off to obtain your test result. Use “very” short probe and ground leads to measure scope results to avoid >10Mhz noise.
Use a CMOS relaxation Schmitt oscillator with RC=1/2f approx. and bias input to skew duty cycle as desired which also raises f slightly using a larger R to V+ or gnd with Vdd =>3x Vgs(th) for low RdsOn to drive low side of R load with Nch FET.
One can also use NPN power Darlingtons but R values must be computed for correct currents and proper power ratings with heatsinks as required.