BLDC Calculation for Back EMF

I have a brushless DC Motor that i am considering buying from hobbyking.com with 2100Kv (RPM/v) i am trying to follow the equation on Wikipedia's motor constants page i have included the equation here but i am having difficulty understanding whether i am using the calculation correctly.

My calculation is 60/(2 x π x 2100) = 0.00454 Nm/A and this should be the value of Kt described above, also because Kt = Ke my back EMF constant will also be 0.00454?

Can anyone help me understand if this is correct?

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 & 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

• your answer seems correct but i am unsure as to whether i understand it, where did you get the 219.911 what calculation did you do to get that and could i use the 0.0045473 in other equations such as to find torque at a given current 0.0045473*105=0.0154nm? – Chris James Dec 5 '17 at 14:55
• 219.911 is the Kv expressing in rad/s/V as oppose to rpm/V. Basically 2100*(2pi/60). This is exactly the same as the wiki equation you have stated EXCEPT each step is very clear rather than a non-derived equation being used without any information as to what is being done. – JonRB Dec 5 '17 at 15:32
• also 0.0045473*105 = 4.774665Nm.... ie 105A would produced 4.77Nm of torque. do you really mean 104Amps. – JonRB Dec 5 '17 at 15:34
• Yes 105amps I know it sounds a lot but I'm working with RC hobby motors. Off topic I'm programming a calculator application for motors so it's easier for people to plug in values and get an answer. – Chris James Dec 5 '17 at 17:07
• Well it isn't a lot, its a relative consideration. The reason I asked did you mean 105A is because your maths does not make sense. You wrote: " 0.0045473*105=0.0154nm? " while 0.0045473*105 = 4.774665Nm thus either your current was wrong or your maths was wildly wrong. – JonRB Dec 5 '17 at 17:10