"Terry Pinnell" wrote in message
news
I made my Curtain Controller 6 years ago based on a motor I stripped from
an
inexpensive battery-operated screwdriver drill (3V). In general it has
worked
fine. But for the last year or two it has developed a strange intermittent
fault. Suddenly, instead of opening or closing the bedroom curtains in
under
2 seconds, it will become glacially slow, taking maybe 10 seconds or so.
Although it always gets there in the end (closing the appropriate
microswitch), it's irritating.

I don't mean 'intermittent' in the usual sense. It continues in this slow
mode for several *months*. Then, just as suddenly, it will revert to its
normal fast mode. And stay that way for months.

A few days ago it once again reverted to slow mode, perhaps the 3rd or 4th
time in 2 or 3 years. I made an even more concerted but fruitless effort
than before to isolate the cause. It's definitely *not* the batteries, my
primary suspect. I've tried several sets of 3 x NiCd/NiMh C-types,
well-charged, all giving identical results. Voltage during operation
remains
more than adequate for the 3V motor. I'm also sure it's not the mechanics,
friction, obstruction, etc.

Logically that seems to leave only the motor itself. Is it possible for
such
a motor to exhibit this sort of behaviour and if so what's the likely
cause
please? Is it fixable or am I going to have to find an identical motor?

--
Terry, East Grinstead, UK

Bad brushes and or dirty commutator is the most likely cause. Clean or
replace the brushes. If possible chuck up the motor rotor in a lathe and
lightly sand the commutator exposing fresh metal, blow clean. A three volt
motor has almost no voltage "head room" to allow for loses in the
brush-commutator junction. Dirt and bad contact can cause the loss of half
of the drive which is what you apparently experience. A higher voltage motor
is much less prone to such failures.