I have acquired a small surplus stepper motor and gearbox. I spoke to the makers of the gearbox (Weyer Bros Ltd), and they inform me that the motor was made about 20 years ago by a company called Cauldron which is no longer trading. Later, another company called Julius Sax made the same motor, but I understand that they have disappeared too. Unfortunately they could not give me any help regarding the motor, but they did say that they have had several similar enquiries in the past.
Does anyone have any information and/or suggestions for a suitable driver board? The motor has the following limited markings:
Type C115, Supply Voltage 28v dc, Steps/rev 10 The connection lead colours are Black, Green, Red, Blue and Orange
If it is a 5-wire, unipolar motor (which seems likely), then it will be "star wired" with one of the four wires at the centre of the star and the other 4 at the points. If you measure the resistance between pairs of wires, you will find one wire for which the resistance to each of the other 4 is the same; this wire is connected to the centre of the star. The other 4 are connected to the points; you will find that the resistance between any two of these four is near enough twice the resistance between any one of the four and the centre wire.
(By the way, if you find that, for each wire, there are two wires to which the resistance is R and two wires to which the resistance is near enough 2R, then what you have is a 5-phase motor with the phases connected in a ring, and all bets are off as the drivers for these are probably going to be more expensive than tossing the motor and buying a conventional stepper and driver. However, this is unlikely.)
Unfortunately, the four coils of the motor are paired; it isn't at all obvious how to determine the pairings in a 5 wire motor (or an 8 wire motor, for that matter). Think of the 5-wire unipolar motor as having two centre-tapped windings, as in a 6-wire stepper, but with the centre taps strapped together; what you are trying to discover is which of the "points" are connected to each end of the two windings. If you don't get this right, the motor won't run.
One method that I have heard of (but not tried) goes as follows:
Number the wires 1 through 5, where 1 is the centre of the star.
Connect a power supply of suitable voltage/current (doesn't need to be the full 28 volts for this) with the +ve to wire 1 and the -ve to wire
The rotor may step to a new position if the rotor was not already at the right step position. Disconnect the supply; the rotor should stay put. Re-connect the supply, this time with the +ve to wire 3 and the -ve to wire 1.
If the rotor stays in the same step position, then you have found the
2 end points of one winding (and the other 2 wires, 4 and 5, are the endpoints of the other winding).
If the rotor steps to a new position, then you know that wires 2 and 3 are endpoints of different windings; repeat the process using wires 1,
2, and 4, and at that point, it is possible to work out what the pairings are.
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