More research on stepper motors
Oct. 25th, 2011 06:16 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
johnridleyAccording to this page on stepper motors, the six-wire motors that I have can be legitimately used the way I'm wiring them (both the original way and the change I made last night).
I was concerned that perhaps there were four discrete poles, two adjacent ones for each winding (one on either side of the center tap) and that they were just connected for convenience. However, that reference indicates that there is only one pole per set of windings and the center tap is actually JUST a tap in the center of one big winding. So using only the half between the center tap and one end is totally legit.
It seems that the 6-wire steppers are used because it allows control with super-cheap electronics; just four 2n2222 transistors could easily drive a stepper. Otherwise you need two H-bridges, with 8 transistors. If you're doing it in custom silicon like a Pololu driver, then the electronics parts becomes basically free and you go full bipolar to make the motors a few cents cheaper, but if you are doing it with discrete electronics, it probably swings the other way and spending an extra few cents per motor reduces the parts count by 4 transistors, 4 diodes and maybe some other stuff.
It's not as strong as the right motors would be (30 ohm versus about 3 ohm coils, so 12/30=.4 amp max versus the amp they usually run at) but given that it should be at least twice as strong as what I have now and that's very nearly working, it should be totally sufficient for at least the extruder and the Z axis. I will still drop in new motors for X and Y since having them be as strong as possible will significantly affect the maximum printing speed.
I will keep the other 3 motors on reserve and replace the rest of them at the first sign of trouble from any of the other motors. Or maybe when I'm just bored some day.
For future reference, Pololu electronics sells 200 step NEMA 17 motors with 2.7 ohms per phase for $14.95, so that's probably the place to get them, since a builder would probably be buying driver modules from them anyway.
I was concerned that perhaps there were four discrete poles, two adjacent ones for each winding (one on either side of the center tap) and that they were just connected for convenience. However, that reference indicates that there is only one pole per set of windings and the center tap is actually JUST a tap in the center of one big winding. So using only the half between the center tap and one end is totally legit.
It seems that the 6-wire steppers are used because it allows control with super-cheap electronics; just four 2n2222 transistors could easily drive a stepper. Otherwise you need two H-bridges, with 8 transistors. If you're doing it in custom silicon like a Pololu driver, then the electronics parts becomes basically free and you go full bipolar to make the motors a few cents cheaper, but if you are doing it with discrete electronics, it probably swings the other way and spending an extra few cents per motor reduces the parts count by 4 transistors, 4 diodes and maybe some other stuff.
It's not as strong as the right motors would be (30 ohm versus about 3 ohm coils, so 12/30=.4 amp max versus the amp they usually run at) but given that it should be at least twice as strong as what I have now and that's very nearly working, it should be totally sufficient for at least the extruder and the Z axis. I will still drop in new motors for X and Y since having them be as strong as possible will significantly affect the maximum printing speed.
I will keep the other 3 motors on reserve and replace the rest of them at the first sign of trouble from any of the other motors. Or maybe when I'm just bored some day.
For future reference, Pololu electronics sells 200 step NEMA 17 motors with 2.7 ohms per phase for $14.95, so that's probably the place to get them, since a builder would probably be buying driver modules from them anyway.
