Dissassembly of Nema stepper motor

[Zip Zap]

Can anyone show me a link on how to disassemble a Nema stepper motor?  Mine has a detached wire and needs to be reinstalled inside.

[Ethan Dicks]

On Fri, May 20, 2011 at 11:28 PM, Zip Zap <zza...@yahoo.com> wrote:
> Can anyone show me a link on how to disassemble a Nema stepper motor?  Mine
> has a detached wire and needs to be reinstalled inside.

Here's a video...

http://www.thetechrevolution.com/makerbot/building-the-makerbot-%E2%80%93-step-4-5-%E2%80%93-fixing-a-stepper-motor/

-ethan

[Zip Zap]

Thanks for the link.  I had a hard time prying it open with a screwdriver.  After watching the guy on the video do it easily, I was able to get it off easily on the second attempt.  It was more mental than muscle.

---

From: Ethan Dicks <ethan...@gmail.com>
To: make...@googlegroups.com
Sent: Fri, May 20, 2011 8:44:40 PM
Subject: Re: [MakerBot] Dissassembly of Nema stepper motor

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[Ed Nisley]

how to disassemble a Nema stepper motor?

That's the easy part. The hard part is remagnetizing the rotor...

At the stepper motor factory, they (with some exceptions, your mileage may vary) magnetize the rotor after assembling the motor, by putting the whole motor in a giant electromagnet with carefully shaped pole pieces, then clobbering it with a monster pulse. Because the rotor is held in place, this actually works.

The alternative requires carefully slipping a pre-magnetized rotor in place using an alignment fixture that prevents it from flopping around. We shade-tree mechanics don't have that fixture.

Anyhow, when you take the thing apart, the rotor smacks against the stator, its magnetic field shorts through the armature, and  that partially demagnetizes the rotor. That's the hand-waving explanation, but it's close.

The motor will seem to work after you put it back together, but the rotor has only a fraction of its original magnetization and so develops only a fraction of its original torque. If that's enough for what you're doing with it, all's well, but you may find the motor doesn't work nearly as well as it used to.

It's much better than no motor at all, so you have nothing to lose...

Good luck!

[Brian Stott]

If touching two magnets together shorts them. How do we have any magnets left? And if touching two magnets has a detrimental effect how do we impart and generate magnetism through rubbing magnetizeable materials together?

Isn't the energizing just a process that initates the field as part of a final assembly/manufacturing step?

I've seen mfg./repair of motors and none have included any concern of the rotor or stator or cases toucing thing around or grounding as with electronics.

What you mention makes the field sound very fragile and could be erased with an earth magnet or degausing (sp?) device.

Is it really that sensitive? Seems then wrong the settings and poor operation in driving the motor with the wrong currents could upset the fields then?

How does the Joe bench guy fix these motors we've had around for decades? What new tools are there to make or acquire here too?

---

From: Ed Nisley <ed.n...@gmail.com>
Sent: Saturday, May 21, 2011 7:24 AM
To: make...@googlegroups.com
Subject: [MakerBot] Re: Dissassembly of Nema stepper motor

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[Hunter]

It's not a short per-se. When a magnet hits something the physical shock will partially demagnetize it. Few things will hit another magnet harder than another small powerful magnet so if you let them smack together then they will be noticeably weaker.

[Ed Nisley]

How do we have any magnets left?

Basically, high performance magnetic material is sensitive to the flux density inside it. The air gap between the rotor and the armature poles keeps the flux density within the specs. When you take it apart, the rotor whacks up against the pole pieces, the flux density goes through the roof, and that's what demagnetizes a chunk of the rotor.

Isn't the energizing just a process that initates the field

Exactly right. But that field depends on the rotor magnetization and that's what gets killed.

mfg./repair of motors and none have included any concern of the rotor

None of those have permanent magnet rotors. "Ordinary"  AC and DC motors produce an electromagnetic field in the rotor and stator; there's no permanent field except in piddly little DC motors with permanent magnet stators. Those don't use the weird & delicate high-performance magnetic materials found in stepper rotors, so they don't have much tendency to demagnetize themselves.

could be erased with an earth magnet or degausing (sp?) device.

driving the motor with the wrong currents

None of those come close to producing the flux densities required to make a dent in the rotor. But there's no point in trying, is there? [grin]

How does the Joe bench guy fix these motors we've had around for decades?

Joe charges way too much to justify working on $20 stepper motors, which really don't have any serviceable parts inside and, apart from the odd wiring failure, rarely fail in use. He works on DC motors with brushes and AC motors with starting caps, which are larger and more expensive, plus they have parts that actually wear out: he can make good money there!

Plus, those motors can be taken apart without damage, because the rotors aren't magnetized.