(ET) E-20 rebuild report

["Christopher Zach" <czach computer org>]

Well, it's in the 60's today, so I decided to go out and take a look at the
E20.

My first thought has been to work on the mower deck while waiting for the
six batteries for the E20 proper. So I took a small 12v battery (5ah) out 
to
the mower and hooked it up to the power line.

Two of the motors started spinning. Good. THe third however was dead. Drat!

Time to drag the mower over to the shed. I took a pair of jumper cables and
hooked the mower to the shed's 24volt mains. Once again, two motors took
off, one dead.

Drat again. Time to take apart motor#3.

First problem was getting the motor apart: One of the screws on the top of
the yellow cover was shot. Cut off the screw and removed the top. There
appeared to be a *lot* of white fluffy stuff all over the inside. Wasn't
sure what it was, so I just cleaned it off. Packing or waterproofing
perhaps? Any clues?

Regardless, I then looked at the motor and hooked the 24 volt power to the
two studs on top. Gotta be the brush power, right?

*WRONG*

Big spark and a hiss before I could pull the wires. I thought I blew up the
armature or something. However upon closer inspection I realized I shorted
and blew up the temp breaker on top of the motor.

Drat. Anyone got another one? Any idea where I can get another one?

Lesson one was learned: When experimenting with something, always start out
with nice, small batteries. If I had continued testing with the 5ah 
battery,
I probably wouldn't have blown up the sensor.

Regardless, I took off the bolts and removed the top of the motor. There 
are
three washers between the motor top and the armature bearing; use care when
removing the top.

With the top off I spotted the problem: One of the two brushes was sticking
in it's carrier. Because it was stuck, it wouldn't move forward as the 
brush
wore, and eventually lost contact with the armature. I wonder if this is 
why
the owner stopped using the Elec-Trak.

With a pair of needle-nose pliers, I gently bent the carrier into a more
square shape and put a dab of oil on the brush. Bingo; it now moves nicely.
Put a drop of oil on the bearing, reassembled the motor (tough to get those
washers in there right) and bolted it all down.

Put 12 volts across it, motor spun up. A trifle noisy; I am not sure why,
but it spins. Hooked all the motors together and dragged out another pair 
of
little 12 volt batteries.

24 volts: roar...

36 volts: ROAR!!!

The mower deck is now operational! Now all I need to do is paint the rust
with POR15 and find some nice yellow top paint!

Thoughts:

The mower motors are drop-dead simple. If they don't run, and they turn,
there are really only two possibilities:

1) The brushes are either stuck or burned out
2) The armature is burned out.

Given the size of the armature wires, I think it would take a lot for #2 to
happen. Thus I'd be willing to bet that most motor problems might be
traceable to a stuck brush. It's possible that one could wear the brushes
down, but it doesn't look likely.

The bearings also seem to be quite sturdy; is it ok to oil those with a 
drop
of oil? Also is there some sort of gasket that's supposed to go between the
brush housing and the motor core?

Next step will be sharpening those blades. Does anyone have a picture of
what the blades should look like shape-wise?

Chris