I am designing a linear telescopic system that gets elevated with a step motor, but to find the compatible motor, I need to work out the torque that is required for the elevation. I have uploaded my CAD model to this thread with how cables are connected. Could someone please teach me how do I go about calculating the torque that is required? it is even more difficult with a pulley that is also moving up in the system. Thank you in advance...
You can workout the tension in the rope using energy/work principle. In stage one, the mases will move a distance of h1, the work done equals to W1 = (m1+m2+m3)gh1 = T1r. Assume your design can stop mass 1, then the additional work for mass 2 and mass 3 to reach the final position is W2 = (m2+m3)g(h2-h1) = T2r. Thus at the end of the journey, the total work done W = W1 + W2, and T = T1 + T2 = W/r.
If we assume no friction and ignore the mass of your jack, because of the moving pulleys T tension will be 1/4 of the weight at the step motor:
let's assume your weight to be lifted is
w =100kg= 980N
T tension in cord= 980/4=245N
r the radius of the step motor pulley is 2cm
then the torque required is t=Fr
$$\tau_s= 245*2/100=490N/100= 4.9Nm$$
kamran has already done the maths for you. You seem to be confused about the cable geometry.
Figure 1. Note that when taut the short sections of cable should be as close to vertical as possible.
The cable will have a certain tension, T. The amount of lift that tension can generate is T cos θ where θ is the angle between the string and vertical. When θ is zero, cosine is 1 and that gives maximum lift.
Failure to keep the short sections vertical means that the tension must increase by a factor of 1/cos(θ) the higher the load is lifted.