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From: Terry Pinnell on 22 Mar 2010 03:45
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
From: Sjouke Burry on 22 Mar 2010 03:59
Terry Pinnell wrote:
> 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 contact with the rotor commutator, a bad connection
in the field coils or the rotor coils, a bad on/off switch,
loose screws on the (internal) motor wiring ....etc....
Most probable the commutator contact, or an intermittent break in
one of the rotor coils.
Unless that last one is just on the commutator connection,
it wont be easy to repair.
From: N_Cook on 22 Mar 2010 06:43
Terry Pinnell <terrypinDELETE(a)THESEdial.pipex.com> wrote in message
news:or6eq5dq330c0j4q8vft3vtdfasp8njm7g(a)4ax.com...
> 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


I would settle for "if it ain't actually broke, don't poke", live with it
knowing that there is a break in the internal wiring and sometimes the motor
will run like a washing machine motor in wash cycle rather than spin cycle,
designed-in in that situation


From: mike on 22 Mar 2010 07:01


Terry Pinnell wrote:

Have you looked at the brushes? Perhaps they're binding in the brush-
holders, or getting to be
too short.

Mike

From: Tim Wescott on 22 Mar 2010 10:27
Terry Pinnell wrote:
> 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?

When you were measuring voltages did you measure the voltage at the
motor, or upstream? You could have a bad connection between your
battery and your motor which would leave your battery as happy as a
clam, yet leave your motor under fed.

Have you checked for mechanical resistance? Perhaps the mechanism is at
fault, and the electronics are fine.

If the motor isn't seeing excess back-torque, and it's getting proper
voltage, then the problem is the motor. If not -- not.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
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