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Stepper Vs Servo Motor Torque Curves Part III

NEMA23 Single Stack Motors

In this post, I’m going to look at some fun NEMA23 single stack servo motors and a single stack stepper motor.  The entrants are:

  • In brown, the PacSci M21 with Sigmax technology.  The M21 has a lot more torque than many (most?) NEMA23 single stack steppers.
  • In blue and red, one of my favorite motors: the BH02300 servo motor.  I’ve spun one of mine at 20,000 RPM.  Like the Emoteq QB series, the BH series has great peak torque.
  • In yellow and green, the MCG (now Ametek) I2351014NC servo motor.  After all the high end motors, I decided it was time to feature a non-exotic and affordable (if you can get it) motor.

Comments

  1. The difference between the I2351014NC and the BH02300 is the peak torque (the BH02300 has much more) and maximum speed (20,000 RPM vs 12,000) and, of course, price; continuous torque is about the same.
  2. Both servos are can go much, much faster than the M21 stepper (although at 3000RPM, it’s pretty fast for a stepper motor).
  3. The M21’s continuous torque looks pretty good; it always has more continuous torque than either servo, and below about 2000 RPM has more continuous torque than the I2351014NC has peak torque.
  4. OK, it’s not really far to compare these motors — they obviously have their own areas (low end torque and low cost for the M21, high speed and moderate cost for the I2351014NC, and high speed, high peak torque, and high cost for the BH02300) but it’s fun to see big differences between motors that are all about the same size.

 

April 25, 2013   No Comments

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.

Comments:

  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.

 

 

April 24, 2013   No Comments

Stepper Vs Servo Motor Torque Curves Part I

While I was working on my upcoming project, I got sidetracked by the issue of servo motors versus stepper motors.  Since I’ve never seen direct stepper and servo torque curve comparisons, I created four comparison charts using a variety of interesting motors.

Disclaimer:  I graphed all the torque curves myself, and their shapes should be pretty accurate; however, I didn’t have very good data for some motors (e.g. Emoteq peak torque).  Motor pricing can very quite a  bit, depending on the exact model and quantity ordered, so any pricing is a rough guide.

If you click on the images, you will get a much bigger version.  To avoid a megapost, I’ve split this topic into multiple posts.

Now that the preliminaries are out of the way, let’s start with the first contestants.

NEMA23 Motors

NEMA23 Torque Curves

First up is a pair of motors: the Kollmorgen AKM21G single stack NEMA23 servo motor with 75V winding and the Pacific Scientific P22 double stack NEMA23 stepper motor.

I picked these motors because 1) they are both from the same company (Danaher), 2) I’ve used both, 3) they’re about the same size, 4) are designed for similar voltages, and 5) both are high end motors, so they should show off the best of their technologies.

The colors are as follows:

  • Red – AKM21G peak torque
  • Blue – AKM21G  continuous torque
  • Green – P22 at 72V
  • Yellow – P22 at 24V

Comments:

  1. Notice how quickly the P22’s torque falls off at 24v – at slow speeds, torque is about 150 oz-in, but it’s  <50 oz-in by 1000 RPM (substantially less than the AKM21’s continuous torque).
  2. The P22 is considerably better at 72V – the torque curve is much flatter, and it has more continuous torque than the AKM21G up to about 2100 RPM.  The higher drive voltages reduces the effects of the stepper motor’s inductance.
  3. Servo drives are the only option for higher speeds.  The AKM21G is rated at 7800 RPM max, while the P22 torque curve only goes to 3000 RPM.
  4. The AKM21G has a much flatter torque curve, especially continuous torque.
  5. The servo’s peak torque is a big advantage: the peak torque available from the single stack AKM21G is ~50% greater than the maximum P22 stepper torque.  The peak torque advantages gets much bigger as the speed increases.
  6. On the other hand, the servo is much more expensive: an AKM21G will run $400 or more, while the P22 is around $100.

March 30, 2013   No Comments

Connecting Emoteq and PacSci Motors to Copley Drives

Copley Stepnet Connected to Pacific Scientific Stepper Motor

Stepnet with PacSci Stepper Motor

I’ve decided to document all the motor/drive connections that I make using my CANOpen drives.  I hope that others will find this information useful.  The first two are up on my trac site:

It was a lot easier to connect the stepper motor, but the servo motor is more fun.  It maxes out at 7,500 RPM using my Logosol power supply.

November 17, 2008   No Comments