Start Position on SY35ST36-1004A

How do you determine the start position of the Motor, on the datasheet here there is no information, on other forum it says run the motor to stall. To me this only means that you have now alligned the gears. no where on the data sheet does it say the motor only rotates 360 degrees, then you have to run in reverse. My question comes as we have this motor, and attach a cam, and on one device the cam appears to be all the way open and on the other device the cam appears to be all the way closed. at power up it appears that the motor is doing stall to allign the gears, but it appears to have no motor rotation. so I am unclear what stalling the motor does, as we do not have an encoder or any other limit sensor, all we have is motor driver. that can rotate forward and backward, ho do I determine start position or home position? so for instance lets say my application power up and rotated the motor 32 steps, then we lost power. When I power up again, I have no idea that the motor is at 32 steps, because I do not have a limit switch, or an optical encoder, If I run my program again, and move the motor 32 steps, it is now at 64 steps instead of the intended 32 steps, because of where it ended before loosing power. (unknown starting position). This would be similar to rotating the motor farther than 360 degrees. for instance if my motor has 200 steps, and I rotate it 247 steps, then loose power, because my start position is unknown, (no way to allign at known gear) if I run the same program, and rotate another 247 steps, motor position is really at 494 steps.


It is really unclear what you are asking. It seems like your mention of “gears” is referring to the internal workings of our stepper motor, but there is no gearbox or any internal gears in our stepper motors. Also, there are no inherent limits on how much a stepper motor can rotate; they make steps when a controller commands them to, so they can be commanded to rotate an arbitrary number of revolutions.

It sounds like you might be trying to determine how to incorporate feedback into your system. Our stepper motors are open-loop devices and do not have feedback. They can be moved a precise number of steps if the mechanical load on the motor does not prevent the output shaft from moving. Also, feedback sensors like absolute encoders or limit switches can be designed into a system using a stepper motor to determine the position of the motor or the load it is moving after a power cycle.


With steppers, most people use a “limit switch” activated by a lever attached to the shaft, or at an end stop. Upon power up, you drive the stepper motor until the limit switch is closed or opened, and that is used as your starting position. If the stepper isn’t overloaded (so that it skips steps), you will always know where it is until power down.

yes, thanks, i read some other stuff off motor operation on the internet. so what I was calling gears, I guess is actually internal magnetic poles. so you apply a pulse to the motor, it energizes a coil making a magnetic pole, the internal motor alligns with this. I was calling this a gear as in a gear tooth, yes there is no gear inside, my bad. so if you want to step the motor, the driver applies another magnetic pulse to the other coil which is offset by the stepping degree of the motor. In my case the SY35ST36-1004A is claiming to have 200 steps which is 1.8 degrees. so my question / comment is because there is virtually no information provided in the data sheet, is there a way to find a home / starting position. meaning is all the poles equally alligned at 1.8 degrees? or is there one pole that can be positioned so the shaft starts in a know position? allowing firmware to figure out where it is vs having to use external switch or encoder. Our current application power on, then the motors buzz but dont turn so I am assuming this means they are trying to allign the motor poles to some kind of start position. Then if you push buttons on the application the motor moves back and forth. I don’t know what the buzzing is but am assuming that they are turning on the coils, but no shaft rotation?

[quote=“jeff_at_eng-genius, post:4, topic:9754”]
is there a way to find a home / starting position
[/quote] Only with an external switch or absolute position shaft encoder.

“Buzzing” usually means that the stepper motor is being inadequately powered, overloaded or driven too fast.