The  Mathematics deduction formule, for calculating the torque of an electric or other type of motor.

                          Per definition : 

We may previuosly consider  the next parameters:

Work =(Force) x (distance)   formule (a)

                           W= F x d,

we can writte F= P  also;

when a turn is complete  N= r.p.m. and for many turns, 

the expression(b) is (2)(Π)(R)(N) is the distance to move in determinate time.

Now, R is equal  to 2r, 

but diameter (R), is equal to  2 r,  ( 2 radius)

Then: R= 2r      expression (c)

and  W=PxR, but   we may know,  that is the torque motor T=PxR, and  (1CV)= ( (75 Kg_m) /  (Sec))

the other equation  
1Hp = (33000 lb_ft / Min),

if,  we do a sustitution with this terms in next expression 
we will have.

HP= ((P)x(2x3.1416)x(r)x(N) / (12)x(33000))

where the   conclution  is:

 Power  in the axis of an electric motor or any machine is:  
Hp.= (P)x(RxN)/63 000)

the result is      HP=((T)x(N)/ (63000 ))

Where the involucrate variables are:

HP,  horse power  is the power of the motor or  any machine

T, is a  Torque  in  (lb_pulg.)

and N, is the turns per minute number  or r.p.m. 

I will be very thankeful if you can  comment about this topic, that I wrote for you. I hope  to recibe some soon.

"Is good to know, but is better you can apply a little of the knowledge, or not ?"
 This is my personnal thinking  away.

Sincerily   Eng. Miguel Ismerio Espinosa