## Understanding Speed-Torque Curves

om_tech_support_JT
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### Understanding Speed-Torque Curves

Q: I am looking at the PK244M-03AA step motor specifications as well as the speed-torque performance curves. This is on page A-294~A-296 of your 2012~2013 general catalog. I'm interested in using this motor for its 0.9 deg full step resolution to hopefully lower some vibration in my machine as well as increase positioning accuracy. I have a couple of questions.

1. Why does it not show the specified holding torque (36 oz-in unipolar) on the speed-torque curve? The curve doesn't extend all the way to zero speed.
2. If the motor's rated voltage is 12vDC, does it mean that I have to supply 12vDC to the motor or use a 12v driver?

A: By the way, if you find that the PK244M-03AA motor does not reduce your vibration or increase your accuracy enough, you can also try our 0.72 deg or 0.36 deg full step high resolution step motors as well.

The holding torque shown on page A-294 and the operating torque shown on the speed-torque curve on page A-296 are treated as 2 separate data. Holding torque is the resistance of the motor shaft while at a energized but standstill state. The motor is not running at this state, but both the motor and its driver are powered. The speed-torque curve is based on actual test data when the motor is running. We actually run a torque test on our motors at specified speeds, then plot the curve. On our speed-torque curves, the curve does not extend all the way to zero speed. The speed-torque curve better depicts the motor's actual operating performance so it's considered more critical than the motor's holding torque.

The motor's rated voltage actually means the minimum voltage you'll need to provide in order to have the motor output its specified holding torque. This is the opposite of the rated current of the motor which is the maximum. The more voltage you provide the motor, the more torque your motor will output in the high speed region. You can actually see this difference in the bipolar-series speed-torque curves since we show both 24v and 48v curves. So if your motor doesn't have enough torque in the high speed region with a 24v driver, try a 48v driver. Just don't use a driver that outputs lower voltage than the motor's rated voltage. Unfortunately, the speed-torque curves we have on our catalog/website are all we can provide. If you want to know how a PK244M-03AA motor would perform with a 60v driver, for example, you will have to make an educated guess from our existing curves and test to make sure.

goodrrz1234
Posts: 1
Joined: Mon Sep 19, 2016 12:22 am

### Re: Understanding Speed-Torque Curves

That is fine It takes decisions .