Page 159 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 6 Options for Creating and Controlling Motion 139

Some other features of stepper motors you might see are detent torque and dynamic
torque. Detent torque is the torque of the motor when it’s moving from step to step,
which is lower than the holding torque, since the shaft is between two holding
positions. Dynamic torque is kind of an average of detent and holding torque, and is
3
approximately 65% of the holding torque. As a rule of thumb, don’t expect a stepper
motor to give you more than 65% of the rated holding torque while it’s pulling or
pushing something.

The information included on this feature list is enough to choose the motor, but once
you have it in your hands, you’ll need to know some more details before you can use
it—like how to mount it and which wire is which. Luckily, on SparkFun’s web page for
the motor, there is a link to the data sheet shown in Figure 6-12.

Moving from left to right on the diagram, one of the first numbers you see is the
diameter of the shaft. Diameter is denoted with the ø symbol, and in this case is
5mm. You also see two small numbers to the right of this, which represent the
tolerance of the shaft. They indicate the range of actual dimensions for the 5mm
shaft. The small 0 on top indicates the largest shaft size is 5mm + 0 = 5mm, and the
bottom number –.013 means that the shaft can be as small as 5 – .013 = 4.987mm.
This will be important in the next chapter when we talk about attaching things to
motor shafts.

Farther along to the right, you see there are four M3 tapped holes that go 4.5mm
deep. M3 is a standard metric screw, and you’ll need four of them to mount this
motor. There must be no more than 4.5mm of the end of the screws sticking into the
motor, or they won’t fit.

The wiring diagram on the right shows that the red and green wires control one
phase of the motor, and the yellow and blue ones control the other. This will be
important when we get to the “Motor Control” section. You’ve already learned about
the important columns in the table in Figure 6-12. The additional information is nice
to have, but doesn’t matter to us, so feel free to ignore those values, and definitely
don’t let them confuse you.

AC Motors

You’ll find AC motors in many household appliances, like blenders and fans, because
they are continuously rotating and use the AC from the wall to drive them. They can
be useful if you have a stationary project and just need a plug-and-play motor that