Risk of stripping or damaging belt in stalled system

    I have a PTZ camera which I am wanting to modify/extend. It currently uses Nema 14 (I believe, see below*) steppers for pan and tilt approximating something like 14HS10-0404S*** from Stepper Online (again, see below*). The gear on the end of the motor is 14 teeth, the gear the belt is driving is a larger gear of 55 or 56 teeth. The larger gear mounts to the yoke (pan) or the actual camera enclosure (tilt). The belt** is 4mm width, 2mm pitch. I am wanting in some situations to intentionally be able to stall the system by holding the camera enclosure in a fixed position. Am I at risk of stripping or damaging the belt doing this? Or what about damaging the motor? I have observed that when the stepper is holding, I can rotate the camera (thus apparently overcoming its holding torque) without much effort.

    I would like to know the ramifications of this with short term stalling (~ 1 minute) and prolonged stalling (> 1 hour).

    * Numbers on stepper motors: 35HS25??F28DL-01, 35HS25??F28DL-02. ?? could either be "M" or "IVI" or ?

    ** Numbers on the belts: B77MXL 4, B116MXL 4 - I believe the 77 and 116 are the number of cogs.

    *** https://www.omc-stepperonline.com/nema-14-bipola…es-14hs10-0404s

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  • Lemster68 June 3, 2025 at 8:36 PM

    Approved the thread.

    One of the advantages of stepper motors is that they don't burn out as easily as brushed motors when stalled. That said, they can still overheat depending on the current limit of the driver circuit and the time it's left stalled. Also, if the driver keeps cycling, the motor is going to keep "twitching".

    As to stripping the belt, it depends. If the motor stalls before the belt/gear start skipping, then you're not likely to damage the belt. Most 3D printers rely on this (and also have low current settings to avoid burning up the stepper motors). But if the belt teeth are soft, the tooth engagement is poor, the belt is loose, and so on, then all bets are off.

    If you drive the mechanism against a hard stop, something is going to give. What that is depends on which item is the weakest link in the chain.

    Quote from SkyeFire

    One of the advantages of stepper motors is that they don't burn out as easily as brushed motors when stalled. That said, they can still overheat depending on the current limit of the driver circuit and the time it's left stalled. Also, if the driver keeps cycling, the motor is going to keep "twitching".

    As to stripping the belt, it depends. If the motor stalls before the belt/gear start skipping, then you're not likely to damage the belt. Most 3D printers rely on this (and also have low current settings to avoid burning up the stepper motors). But if the belt teeth are soft, the tooth engagement is poor, the belt is loose, and so on, then all bets are off.

    If you drive the mechanism against a hard stop, something is going to give. What that is depends on which item is the weakest link in the chain.

    Thank you for your reply. The fact that I can turn the yoke with what feels like little effort, and doesn't feel close to stripping anything, when the servo is holding - does that give any indication of anything? Is the torque of the motor greater when rotating than when holding?

    A stepper motor is like a magnetic "gear" whose teeth can "slip" -- as you force it to turn, the resistance should feel like a series of spikes. You basically force it out of one increment and it falls into the next.

    However, a slipping toothed belt might feel similar. So from the outside of a "black box", it's hard to say which one you might be feeling.

    One of the tests for stepper wiring is to short both wires of a phase together and feel how the resistance changes. If you do that, and feel the resistance of the PTZ change, that would indicate that the motor is what's slipping. If not, that suggests something else is slipping.

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