Likely the plastic rotor outgassed and shrank, breaking the glue bond, not helped by a minimal amount of glue as well. Will take a bet those wires are not copper but CCA wire, as those motors are pretty much all made with it now, as it is a very easy wind, and the CCA wire in there is noty going ot fail, and is a lot cheaper than actual copper. Yes the design is optimised for cost, using the 2 windings as single turns in a bobbin, and the stamped shaped pole pieces, combined with the ferrite dust magnet rings with selective magnetising, so as to make production very fast and repeatable, and very simple, so they can be assembled by low cost labour. Gear is put on the shaft using induction heating, to make it nearly red hot, then pressed into place on the shaft, so it shrink fits on there, so then the iron oxide layer on the surface can have a thin film of oil added to it, to keep it running well and lubricated. Plus those are compressed and sintered powder gears, a blend of fine steel powder pressed into a green shape then fired in a hydrogen atmosphere, to get the final size, and making it porous, so the oil can stay there for life, slowly lubricating the gear running surface, reducing wear. Designed down to the absolute minimum, and designed for ease of manufacture, all parts being either a stamping out of electrogalvanised steel, or a powder metal part, for the gear and bushings, or turned on a CNC lathe for the shaft, which has been polished using a tumbler, then plated in a tumbling basket as well, so all the thusand parts get done the same thin coat of nickel at the same time. All meant for ease of assembly, and then a quick test on the line and into the box for shipping.
Used these motors a lot in the 80's. You could get gearboxes that attached to them with a huge reduction on them. The motors were always reliable, the failure point was the gearboxes due to a mix of brass and plastic gears..
Amazing that it only has 2 windings, I was expecting lots of windings, one for each (or pair of) pole piece. Very clever arranging the stamped out poles so that it cranks in whichever direction you want using only those two windings. They sure 'Kept It Simple' Thanks for the teardown, quick description of fault (could have been more detailed) and analysis of probable sequence / cause of failure. I strongly agree with your ethos of repair if possible/sensible. I certainly get enjoyment from pulling apart failed gear to see why it failed and making an attempt at getting it working again. If I achieve a robust repair there's years of satisfaction to be had every time you see it in use. Having to make a bodgy repair for paying (or charity) customers is sometimes not much fun, it's hard to achieve robust solutions to some of the 'programmed obsolescence' devices around nowadays. Replacing the stepper motor rather than repairing it is probably a good call (Unless, of course, there were no equivalent spares easily available).
Hi Scott, I have seen quite a few small stepper motors fail in this way, it's not uncommon for the badly glued magnets to come unstuck, of course with the magnets spinning the whole thing goes out of sync or steps randomly. Regards, Ray in North Wales..
Likely the plastic rotor outgassed and shrank, breaking the glue bond, not helped by a minimal amount of glue as well. Will take a bet those wires are not copper but CCA wire, as those motors are pretty much all made with it now, as it is a very easy wind, and the CCA wire in there is noty going ot fail, and is a lot cheaper than actual copper. Yes the design is optimised for cost, using the 2 windings as single turns in a bobbin, and the stamped shaped pole pieces, combined with the ferrite dust magnet rings with selective magnetising, so as to make production very fast and repeatable, and very simple, so they can be assembled by low cost labour.
Gear is put on the shaft using induction heating, to make it nearly red hot, then pressed into place on the shaft, so it shrink fits on there, so then the iron oxide layer on the surface can have a thin film of oil added to it, to keep it running well and lubricated. Plus those are compressed and sintered powder gears, a blend of fine steel powder pressed into a green shape then fired in a hydrogen atmosphere, to get the final size, and making it porous, so the oil can stay there for life, slowly lubricating the gear running surface, reducing wear. Designed down to the absolute minimum, and designed for ease of manufacture, all parts being either a stamping out of electrogalvanised steel, or a powder metal part, for the gear and bushings, or turned on a CNC lathe for the shaft, which has been polished using a tumbler, then plated in a tumbling basket as well, so all the thusand parts get done the same thin coat of nickel at the same time. All meant for ease of assembly, and then a quick test on the line and into the box for shipping.
Great look inside a stepper motor, would’ve been good if you could’ve fixed it. Keep up the great work mate. 🤙🏼🇦🇺
Used these motors a lot in the 80's. You could get gearboxes that attached to them with a huge reduction on them. The motors were always reliable, the failure point was the gearboxes due to a mix of brass and plastic gears..
Amazing that it only has 2 windings, I was expecting lots of windings, one for each (or pair of) pole piece.
Very clever arranging the stamped out poles so that it cranks in whichever direction you want using only those two windings.
They sure 'Kept It Simple'
Thanks for the teardown, quick description of fault (could have been more detailed) and analysis of probable sequence / cause of failure.
I strongly agree with your ethos of repair if possible/sensible. I certainly get enjoyment from pulling apart failed gear to see why it failed and making an attempt at getting it working again.
If I achieve a robust repair there's years of satisfaction to be had every time you see it in use.
Having to make a bodgy repair for paying (or charity) customers is sometimes not much fun, it's hard to achieve robust solutions to some of the 'programmed obsolescence' devices around nowadays.
Replacing the stepper motor rather than repairing it is probably a good call (Unless, of course, there were no equivalent spares easily available).
Hi Scott, I have seen quite a few small stepper motors fail in this way, it's not uncommon for the badly glued magnets to come unstuck, of course with the magnets spinning the whole thing goes out of sync or steps randomly.
Regards, Ray in North Wales..
Shouldn't a stepper motor have far more windings?