I agree with you, Ken. The best type of a DC motor for speed control is a PM
(permanent magnet) type. This type is easily controlled by a PWM (pulse
width modulator) system. These controllers vary the average current in the
motor by varying the on/off ratio if an electronic switch (usually a big
power MOSFET these days) at a high speed. There are tricky ways of reading
the motor back- EMF to measure its speed but unless you are really into
power electronics, I'd recommend you buy a controller rather than try to
build one.
Regards, Neil Tucson, AZ
-----Original Message-----
From: SMITH KENTON E [mailto:ksmith6@mindspring.com]
Sent: Wednesday, February 27, 2002 7:28 PM
To: Paul Bland; lsr
Subject: Re: electrics question
Paul.
A lot will depend upon the application. I would visit a local
Bearing/Industrial Motor Control outlet for the specifics. The easiest way
would be with a DC motor and a DC speed control. The speed control is
basically a variable voltage control box that will give a digital readout in
% of full speed, or some other parameter depending upon the model you
choose. If very precise speed feedback is required (sometimes what the
motor is being told to do isn't what it is doing) a shaft mounted speed
sensor would be required. Just like what you would need for a traction
control device! ;-).
Hope this helps.
Ken
#626/GMR
----- Original Message -----
From: "Paul Bland" <paul.blandavon@btinternet.com>
To: "lsr" <land-speed@autox.team.net>
Sent: Wednesday, February 27, 2002 9:06 AM
Subject: electrics question
> List I need some help on a electrical problem, now I'm the first to admit
I
> know about as much about electrics as I do the mating habits of a jelly
fish
> so the answer will have to be in laymans terms. What I need to make is an
> electric motor, about 1/2 h.p. or so (not that important) that I can
adjust
> the speed of, hopefully between 1000 rpm and 6000 rpm, the tricky bit (for
me
> anyway) is I need to know the speed the motor is turning at. I know
this'll be
> pretty easy for some of you guy's but I'm baffled!
> Cheers, Paul.
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