For a while now ive been having issues with my S4 Pro Xl where my machine would start making a grinding noise mid cut. Working with support we figured out that one of the Y axis stepper motors is bad and needs to be replaced. C3D is going to sell me a new one which is great, but sort of frustrating to have a motor go bad after only 2 years of light use. Anyway it got me thinking, is there anything I could be doing or not doing that would shorten the life of the motors? Also, has anyone used motors other then the ones from C3D? In the future being able to source an alternative in canada is always easier.
All electronic devices have a Mean Time Between Failure (MTBF). Some parts last forever and some parts fail as soon as they are powered on.
The most stress on a stepper motor is standing still. So if you are not going to use the machine for a while just power it off. The X Y and Z are remembered by CM and so you can go right back to work after a power off and power on. Sometimes on a long carve I just shut down the machine at a tool change. Then in the morning I disable the previous tool paths and resave the file and start again. That wont work for an advanced vcarve but separate tool paths that works fine.
Sometimes it is the luck of the draw that an electronic part fails. I would not dwell on it and replace the motor and see what happens.
I had a friend that was always worried about the things he had no control over like what if the sky fell. I only worry about the things I have control over. If the sky falls I cannot do anything about it. I can hope if it does fall it does not hit me on the head but that is it. Parts fail and that keeps the whole world working.
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Sometimes we speak legends that need more corroboration before they get misunderstood and passed down to generations to follow. 
IMO pushing the machine past its upper limits will reduce the lifecycle of various parts. Causing the steppers to stall would sink a current that could potentially damage the coils if the current is sustained. Iām not sure if there is any type of protection in the circuitry.
I would think that crashing and high force cuts will cause undue wear on bearings as well.
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Steppers consume full winding current when energised, not like other types of motor whose power is dominated by the applied mechanical torque.
Leaving the controller powered up and the stepper āholding positionā allows them to heat up, the same way they would when stepping. Lifetime of the coils derates with temperature, so leaving them powered up, even not stepping or under load, consumes operating lifetime on the motors.
There are other wearout failure modes on the motor where bearings or shafts can fail when people get enthusiastic on belt tension which are related to motor movement.
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Steppers are actually quite happy stalled, they work by moving from one stalled position to another. Axial load on the shaft is a good way to kill them, spinning the motor quickly when the controller is powered off is a good way to kill a stepper driver with weak protection circuits.
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Good stepper motor drives will cut the current when the steppers are in a āholding positionā. Iāve only had one stepper motor fail on me, and that was a new one, right of the box. One of the coils was shorted, taking out a stepperdrive. Xylotex was kind enough to repair the board at no charge, but the stepper motor vendor claimed that steppermotors never fail, and wouldnāt accept a return.
Hah,
Iād love to find that factory that can make steppers that never fail
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So, for the life of a stepper, it makes no difference whether they are stepping or stalled.
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The TLDR in my opinion;
I donāt really expect the steppers on my Shapeoko to die, theyāre an industrial part designed for both position holding and repetitive motion and weāre just not using them that hard. If they do die, theyāre a commodity part and cheap to replace, Weāll spend less on maintenance parts, belts, steppers etc. than cutters.
I turn the machine off when Iām not using it as thereās no point burning through the stepper life or energy when itās not needed, however, I donāt generally turn the machine off during the day if Iām using it again as Iād have to re-home or re-zero.
In more detail, so far as I understand it (from when I worked with them and later reading more vendor data)
- Electrically
Unless youāre using very clever controllers, no real difference, steppers are designed for position holding as much as moving and when you energise the coils they heat up a bit and the electrical life is related to time and temperature, so hours of being on are hours of life. (no I donāt think thereās significant benefit from motor heatsinks in this application)
Most stepper drivers use constant current drive where they vary the voltage to get the target motor current so there is little difference in winding current at different speeds. Some drives can do funky stuff like detecting low torque and reducing drive current, somebody who knows the Carbide controller boards better could comment on the specific driver, but given the lack of missed step detection, torque warnings and temperature the motors reach when stationary, I suspect theyāre relatively simple constant current drivers.
Hereās a good video from somebody who designs stepper drivers for a living with some excellent oscilloscope graphs of the drive voltages, currents and what happens with back EMF etc.
The video also shows that thereās no real electrical impact of missed steps or a forced mechanical stall.
- Mechanically
Mechanically the motors have a few known wearout characteristics, these are well described in the vendor data. The two key ones I recall are bearings and shaft deflection.
These small steppers normally have two ārealā bearings, simple bearing races at the front and back of the motor, designed to handle radial loads (this is one of the reasons why you donāt attach a leadscrew or ballscrew directly to most steppers but instead use a coupling and locate the screw on bearings designed to handle axial loads as well).
These bearings generally have a wearout life chart plotting radial load against total revolutions, simply, the more radial load theyāre under the more wear each revolution causes. The real world life also depends on temperature, state of lubrication, ingress of fine particles through the seals etc.
The second, less obvious, mechanical failure mode is the snapped stepper shaft when the belt tensions are too high. Under high radial load the stepper shaft flexes and can quite quickly fail due to fatigue. This shouldnāt be a problem if we stick to sensible belt tensions.
There is a mechanical shock load if the linear motion system crashes into an endstop and this will create a peak load on the motor shaft and bearings, but I donāt think the stepper will be the first part to give up under constant crashes.
HTH
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its only $45 small expenditure for 2 years
I like testing thingsā¦
We purchased the S-3 XXL in 2019. I have left the machine mostly powered on for years. No stepper failures yetā¦? Digital temp probe shows about 86 degrees f. at the center of the rear motor housing.
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Coming from a 3d printing background and getting back into CNC itās always good to have 1 of each type of motor laying around as spare parts. A machine will always go down at the worst time and having the parts on hand saves time, money and possibly a job. Also having an extra belt laying around would be a good idea as well. Consider them like cheap insurance.
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