When selecting a DC motor, it is necessary to identify the main performance specifications in addition to the power and size requirements. In a DC motor, the speed can be controlled only by varying its voltage, unlike an alternating current (AC) electric motor whose speed is varied by frequency. Axle speed specifications generally refer to the no-load speed, which is the maximum speed the motor can reach when there is no torque applied. https://www.mrosupply.com/lubrication/lubricants/527798_l0847-060_lubriplate/ Shaft speed is given in revolutions per minute (RPM). We must not forget that speed depends on the voltage and the power, if a proper specification of the DC motor is not made, this may be a limiting factor.
The constancy of the torque is also of great importance. The torque of a DC motor is proportional to the induction current, in which case we have the torque constant. A DC motor is an electric motor that has its switching, which is the exchange of energy between rotor and stator, made through brushes or brushless.