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1063_0_Product_Manual - October 27, 2010 2:54 PM
8 Wire Stepper Motors
8 Wire Motors are very difficult to wire up if you do not have a schematic showing how
the wires are connected to the internal coils. Only follow these instructions if you are
really
desperate.
In an 8 wire motor, the coils are split, and we have to reconnect the coils, to reduce
them to a 4 wire. Assume our eight wire stepper motor wires are colored as follows: red,
yellow, black, orange, blue, green, brown, and white. In an 8-wire stepper motor, these
wires would be part of 4 coils, 2 wires per coil. We need to determine the cable pairings.
We measure the resistance between each wire and are presented with the following
values in ohms (these are simply example values):
This table tells us which wires are parts of a coil. From the table we can tell that red/blue, yellow/green, black/
brown, and orange/white are the coils.
We are now left with the following situation; we need to determine the proper orientation of the wires to determine
our connections. Of each pair, one of the wires will be assigned to A, B, C, or D, and the other wire will be
connected to another pair. The number of combinations to be tried to see if they produce rotation is large, but can
be reduced to a maximum of 96 possibilities by following these steps:
Choose Red/Blue to connect to A. (2 possibilities)
1.
Choose one wire of the other pairs (6 possibilities) and connect to B. The other wire from this pair is connected
2.
to the wire from Step 1 not connected to A.
Choose one wire from the two remaining pairs (4 possibilities) and connect to C.
3.
Choose one wire from the remaining pair (2 possibilities) and connect to the wire from Step 3 not connected to
4.
C. The remaining wire from this pair is connected to D.
After trying each permutation, engage the motor from software and try to rotate it. Do not connect the pairs to
5.
anything - as if you were using a 6-wire stepper in bipolar mode.
If you attempt to use this algorithm, build a table of permutations beforehand and proceed in a systematic way.
There are a total of 96 wiring combinations, of which there are 2 valid combinations where one will cause a
clockwise motor rotation and the other will cause a counter-clockwise rotation.
If you are not using a Phidget stepper, we suggest consulting any manuals or data sheets that are associated with
your particular motor in order to determine the proper wiring for your motor.
Controlling Steppers - Open and Closed Loop
Because stepper motors do not have the inherent ability to sense their actual shaft position, they are considered
open loop systems. This means that the value contained in the current position property is merely a count of the
number of steps that have occurred towards the target value; it can not be relied upon as a measure of the actual
shaft angle, as external forces may also be affecting the motor.
There are several ways of overcoming this drawback. The simplest is to allow the motor load to depress a limit
switch located at a known position. This can be used to fire an event in software to recalibrate the shaft position
values. A more elegant solution might involve the mounting of an optical encoder on the shaft and the development
of a control system.
8 wire motor
+
+
A
B
C
D
Red
Yellow
Black
Orange
Blue
Green
Brown
White
Red
∞
∞
∞
1
∞
∞
∞
Yellow
∞
∞
∞
1
∞
∞
Black
∞
∞
∞
1
∞
Orange
∞
∞
∞
1
Blue
∞
∞
∞
Green
∞
∞
Brown
∞
White