magnets and extruder motor
I recently had an extruder motor fail and was surprised that it did. In the past I put a magnet with a pointer on the motor to track the movement of the motor as it printed. The magnet was a very strong magnet and when I removed it I had very fine black dust on it. Now I think the magnet may have been the cause of the failure as it effected the freedom required for the bearings to turn as they should. As I know that putting such indicators on the motor seems to be a regular practice, it may cause problems in the future for other hobbiests. May be an upper limit on magnet strength used. Any thoughts on this?
RE: magnets and extruder motor
ive often wondered about that, but I think the magnet inside the motor is stronger.
or I should say the magnets alignment in the motor is stronger.
I have a Prusa,therefore I research.
RE: magnets and extruder motor
Depends on why and how to motor failed. It could be a frozen bearing due to shaft loads; winding failure to to heat build up; clearance issue in manufacturing; to name a few. Or it could be magnetization failure for a variety of reasons (poor manufacturing, poor material, a crack developing during use) ...
RE: magnets and extruder motor
First it started skipping extrusion and then stopped all together. Replaced with new motor.
RE: magnets and extruder motor
Kind of a swag, but if the dead motor has an uneven jagged / scratchy feel when spinning it by hand, rather than a nice smooth rotation, it's likely a mechanical failure: bearings most likely. The spin will have the "notchy" feel of the rotor/stator fields, but should be smooth and even.
The Prusa motors are only rated around 11 lbf 1/2" out the shaft; and the Bondtech gear may be exceeding this if the idler is over tightened. Especially on the MK3S where the motor is already biased a bit tight.
If the motor feels smooth, you can ohm the windings to check for differences: they should measure near identical values. A difference above 5% indicates a good chance of a winding failure. You can also short the windings (one at a time) and spin the motor to get a better sense of the fields - and shorting one winding should feel the same as the other. If they feel different, another sign it's likely the windings have failed.
RE: magnets and extruder motor
Extruder motor and skipping is an age old problem. High torque and the motor can get hot. I have come across this in many different printers. Printing slower helps. The extruder seems under strain with the MK3S and does get hot. I suggest a better motor is needed.
Nigel
Life is keeping interested and excited by knowledge and new things.
RE: magnets and extruder motor
I have a Mk2.5. I thought of a heating problem but used a scope and it was no hotter than other motors when it was failing. Reading about 33C. I think PRUSA uses LDO MOTORS. My guess that it is a 1.8 Hybrid Stepper Motor LDO-42STH40-1004ASR #181120. I thought LDO made some of the best motors but if you know of a better motor replacement than I would be interested.
RE: magnets and extruder motor
Check the thread Guy started regarding better motors for reducing surface artifacts... he mentions a few 0.9 degree replacements, has good words for some.
ps: