Re: DC Motors


"Rich Grise" <rich@xxxxxxxxxxx> wrote in message
news:pan.2007.05.28.22.56.03.213552@xxxxxxxxxxxxxx
On Sun, 27 May 2007 18:52:19 -0500, Jon Slaughter wrote:

Does anyone know what kinda motors that most drills use? I was thinking
it
was a torque motor but not sure.

Also, for DC motors can I get away with changing the voltage to a lower
setting to increase the torque or do I run a huge risk of burning up the
motor?(i.e., are they usually designed for a very narrow operating
voltage).
I have this old broken 18v drill and I want to turn it into opening a
gate.
I figure that it has enough torque to do it and I can control the speed
quite easily.

If you already have speed control, don't mess with the voltage. What's
broken about the 18V drill? Right after saying it's broken, you say it has
torque and speed control.

Run it at 18 V and either figure out a trigger setting, or hack the
controller to do with what you want.


Its broken at the shaft. The motor seems to run fine but overall the drill
is broken(you know, there are other parts to a drill). The speed control is
through the trigger and I need to automate it... The "control" is
encapsulated so not much I can do with it. I didn't say it had speed
control though... I said I can control the speed quite easily(by suppling a
lower voltage).

Since it runs on dc either I can use some dc method of power control such as
pwm or AC method such as triacs and rectification(both of which probably
result in essentially the same result). But seems to me using dc and just
lowering the voltage is the easiest thing? I really don't understand what
the point of pwm is as it would ultimate seem to still average out things to
an equivilent voltage supply? (i.e., why not just just lower the voltage in
the first place if I can do that(remember, I don't need to automate the
speed of the motor but just easily be able to find the right speed which
makes the gate open fast enough).

i.e. the issue is not to automate the speed of the drill but to know how the
torque and speed are related to the current and voltage so that when I
guesstimate the right settings needed for the drill to run properly. On
wiki it seems to say that the torque is inversely related to the speed and
that the torque is proportional to current while the speed is proportional
to the voltage. This is very confusing to me and I can't explain why it
happens that way(except that maybe the motor sets up a reverse MMF that
counters the current or something like that) but if its the case then it
seems that running the drill motor slower will give me more torque.... but
might be to slow.

I'm just a little confused about that aspect ultimately I can hard wire the
circuit for the speed as it won't need to be changed(and the motor will not
run much so it doesn't have to be efficient).

Thanks,
Jon


.

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