View Full Version : 10 Minute ETEK Motor Teardown

04 December 2011, 0920
Check it out, bitches:



Nuts & Volts
04 December 2011, 1011
That hammer just comes out of no where man! Nice job. You can definitely see the Agni technology used in the rotor.

I bet you could drill holes in the outer casing to increase cooling, just not too many of them. However, maybe its better just to keep that thermal mass and force more air over it.

04 December 2011, 1137
Yassss yasss. The BFH is never far away in my shop, no suh. ;)

On the cooling... That was actually one of the reasons I wanted to tear it down again, to get a look at where some ventilation on the output side could go. Stay tuned. But there's no airflow whatsoever on that side, just the vents on the outer casing. The problem is structural, I think. That's the end that gets most of the stress and it's pretty much solid. The plate that holds the bearing in, and locates the rotor shaft is solid.


The rest of the diameter of that case is magnet. You either have to drill a bunch of small holes around the bearing holder-inner plate and hope for the best, or maybe one or two very small holes for an air or mist injection system. Here's the thing about it. From everything I've seen the rotors warp when they overheat, and travel to the brush side, until they rub against the magnet and bind up. That is coincidentally the side that is cooled. I'm thinking the motor heats up unevenly from the output side and literally pushes the thing to the cooler side.

Nuts & Volts
04 December 2011, 1158
So you can't drill the two sides, but can't you put holes around whole circumference like the silver part of the agni?? bring air in the front, it runs over the rotor/is push around by the rotor and then exits both through the brush holder and the rear. This make sense?

04 December 2011, 1208
Yeah, esssACTLy. Still, it seems like it wants something closer to the shaft. Does anyone have any cool graphics of motor thermal patterns?

04 December 2011, 1306
Does anyone have any cool graphics of motor thermal patterns?

I don't have any graphics, have never owned or used one, but have seen quite a few failures. The number one failure zone is the brush/comm area. Second are the clips on the outside edge of the armature coils. Thirdly is the axial displacement of the rotor causing interference with the magnets.

The rotor acts as a centrifugal fan so a forced air scheme should provide high pressure air towards the shaft and let it exit around the outside circumference. This would also allow the coolest air to circulate past the brushes first.

FWIW, I have seen other motors where the rotor has displace axially in position on the shaft causing misalignment with the stator. In my case it was caused by incorrectly using a press to change bearings. The rotor was held to the shaft with a press fit without a positive locator shoulder or clip. Could you alignment problem be due to this? That big old hammer might just have moved the shaft relative to the rotor.

04 December 2011, 1329
No, I don't think I moved anything, since it was binding before I starting in with the hammer. In any case, the blows of the hammer would have displaced the rotor in the direction I wanted it to go... which it didn't. (The rotor needs to come back towards the end I was hammering on). Nothing has slipped on the shaft, and the rotor actually does measure out to be warped towards the brushes by just about the right amount - 1/16th" at the magnet outside diameter.

I've also heard several reports of just this kind of thing happening with these motors from overheating, but I don't know that for a fact.

I'm not at all convinced the rotor does any fan action at all. There's no perceptible air movement outside the motor when you spin it up, coming out of the vents, as you'd expect.