Anyone else using these? I see the person who did the kickstarter for a PCB and a library has moved to using grey market driver ICs and no longer does anything with the library. I (meaning we at OlyMEGA's Arduino night) had problems with his X25 library. Chatter, backwards motion, skipping, slipping.
I've seen a number of people trying to use regular 4 wire stepper driver patterns and even chopper driver chips with limited success. Not surprising, as the X27 requires a different step pattern.
So Ross, one of our members, wrote an add-on to the AccelStepper library to drive the special 6 step pattern that is in the datasheet for the X27.168.
It works great! With the right settings in AccelStepper, it moves very much like an analog meter movement.
I’ve used several of these “X” series motors ( which feature in automotive gauges) , with a H bridge controller and the stepper library , with no problems (never finished it , but was making a rev counter that worked like a chronometric tacho. - sold the car!). The motors just have two separate coils . There seems a speed limitation; above which they miss steps ( 270deg in about 2sec) does this overcome it ? Why do they need to be driven differently from other steppers ??
I’ve also used this setup with unknown Chinese steppers found in some cheap stepper type 52mm car gauges and has them working ok.
Thank you for poking me about this. I've had major changes at work that took my time and attention away from this. I intend on getting together with my friend again soon to keep working on this.
@polymorph please do, when you get the time; I would love to use these motors in a project or two but have suffered similar problems (chatter, backwards motion, etc) and don't (yet) possess the know-how to tweak AccelStepper for these things, what with the 3-phase pattern.
The gauge stepper drive pattern is clearly half step, two phase, but with six states instead of the usual eight. Both coils are on in only two of the six states, whereas with the 8 state drive pattern, both coils are on in four of the states.
It isn't clear why the manufacturer chose this particular pattern, but maybe it is to save power, or the rotor is not symmetric.
It is easy to replicate the pattern with some of the standard motor drivers. Adafruit appears to have done that with the TB6612 driver.
According to the Wikipedia page, the Lavet-type is single phase, with a single coil, and three drive states. One is a null state when the coil is not energized. It is unidirectional in motion, probably because of the cogging in the null state.
In the six-state pattern published by the gauge motor manufacturer, at least one coil is always on. Perhaps that is the key that allows bidirectional motion.
Physically, it looks a bit like a 3 phase motor with one stator missing. I opened one up and took a picture sometime last year, but don't know where I put the picture.
It has two windings, and the pole piece comes in about 120 degrees from each other. I don't remember if I discovered the rotor had 2 or 4 poles. It is geared way down.
I have seen a lot of people complaining that using the regular step pattern results in lost steps. I personally observed this. Lost steps, only very slow speeds work, vibrates like crazy, even turns backwards at modest step speeds.
With the new step pattern my friend wrote for the accelStepper library, it moves very smoothly, quiet, and no lost steps.
Here, I found an image of one with the cover taken off:
