constant - 12V DC Motor 350RPM w/Encoder (12kg*cm)

Hi together, 

 

unfortunately I could not find the values for the following properties of the 12V DC Motor 350RPM w/Encoder (12kg*cm) anywhere. 

 

Does someone have the values for: 

- k_t: torque constant [Nm/A]- k_v: voltage constant [V/omega]-  k_: proportionality constant [unitless])- motor efficiency @max. efficiency rpm

Best regards and many thanks if someone them

Tistar