BLDC Calculation for Back EMF
This is correct.

\$K_t\$ is approximately equal to \$K_e\$ (approximatly as \$K_e\$ is defined as open-terminal voltage and \$K_t\$ is defined at rated current &amp; the machine may be saturating) 

\$K_v\$ is the reciprocal of \$K_e\$

The units of \$K_t\$ are \$\frac{Nm}{A}\$

The units of \$K_e\$ are \$\frac{V}{\omega}\$  (NOTE: from a magnetic point of view this is peak line-line voltage...)

so... 2100\$\frac{rpm}{v}\$ == 219.911 \$\frac{rad/s}{V}\$ = \$K_e\$

Thus taking the reciprical of \$K_e\$  

\$K_e = \frac{1}{K_v}\$ = 0.0045473