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Stepper Vs Servo Motor Torque Curves Part II

NEMA34 Torque Curves

NEMA34 Torque Curves

Today I am examining some interesting NEMA34 motors’ torque curves.  The graph is a bit complex because I want to show a variety of motors on one graph; to make it a bit simpler, I am using dashed lines for servo continuous torque, and solid lines for servo motor peak torque.

I chose motors that are all roughly the same size.

The motors and their colors are:

  • Burgandy Red – PacSci N32 PowerPac double stack NEMA34 stepper motor at 75V.  I choose this motor because it’s a high end stepper, and I own a couple.
  • Red – PacSci K32 PowerPac double stack NEMA34 stepper motor with Sigmax technology, also at 75V.
  • Yellow – Emoteq QB03402 double stack NEMA34 servo motor.  I own a similar motor (QB03403), plus the peak torque is very high.
  • Green – Parker Compumotor BE342H double stack NEMA34 servo motor at 170V.  Parker makes some really nice servo motors; the BE series has a lot of torque, and I want to look at the effects of voltage on torque curves.  The BE342H and BE342K have different windings.
  • Brown – Parker BE342H at 340V.
  • Dark Blue – Parker BE342K at 170V
  • Light Blue – Parker BE324K at 340V.


  1. The NEMA34 stepper curves are similar to the NEMA23 stepper curves; torque still drops off rapidly with increasing speed.  One quirk: maximum torque is around 120 RPM, not 0 RPM.
  2. PacSci’s Sigmax technology does provide significantly higher torque at all speeds, but does not change the shape of the torque curve.
  3. Overall stepper vs servo comparison is similar: the steppers have much more continuous torque at low speeds, less continuous torque at moderate speeds, less peak torque at all speeds, can’t handle high speeds, and cost significantly less than servos.
  4. The Emoteq BH03402 has exceptional peak torque, but you’ll have to provide a lot of current (e.g. 50A for the 130V C windings).
  5. The Parker BE342 shows the impact of voltage and winding.  When the servo motor does not get enough voltage, its torque can decrease like a stepper, but for a different reason: back EMF.
  6. The BE342K might seem better than the BE342H, since it has the “best” torque curve, but that comes at price: the same torque requires double the current of the BE342H.
  7. Stepper currents are much lower; the maximum current of any N32/K32 model is 10A.
  8. As always, it comes down to knowing your requirements: torque, speed, size, current, budget, etc.




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