Stepper vs. DC Motor control
Archiver
Posts: 46,084
Greg:
The encoder is just a position feedback device. The DC or AC servo is
controlled via a special amplifier/driver which is matched (voltage wise) to
the voltage at whitch the servo motor operates. Typical DC voltages are from
20 to 90 Vdc. There are quite a few companies out there that make the
amplifiers and the motors however they are not all that cheap. Power supplies
and amplifiers usually run from several hundred dollars to several thousand,
depending upon the application. The motor(s) are additional costs.
Is the homemade encoder designed as a quadrature or just a single pulse?
Quadrature encoders generate two pulses 90 degrees out of phase with each
other and depending upon which edge is leading, the motor is running forward
or reverse. I am not sure about the response time for the SX stamp but I
have a feeling that is is too slow to work very well in any real application
for motion control using the above mentioned hardware.
What exactly is your application? Maybe if we know more about that we can be
of more assistance.
Randy A.
The encoder is just a position feedback device. The DC or AC servo is
controlled via a special amplifier/driver which is matched (voltage wise) to
the voltage at whitch the servo motor operates. Typical DC voltages are from
20 to 90 Vdc. There are quite a few companies out there that make the
amplifiers and the motors however they are not all that cheap. Power supplies
and amplifiers usually run from several hundred dollars to several thousand,
depending upon the application. The motor(s) are additional costs.
Is the homemade encoder designed as a quadrature or just a single pulse?
Quadrature encoders generate two pulses 90 degrees out of phase with each
other and depending upon which edge is leading, the motor is running forward
or reverse. I am not sure about the response time for the SX stamp but I
have a feeling that is is too slow to work very well in any real application
for motion control using the above mentioned hardware.
What exactly is your application? Maybe if we know more about that we can be
of more assistance.
Randy A.
Comments
One more question: The controller one would use for a DC or AC motor
encoder, how would you read and command that from a Stamp? I've seen
stepper controllers that one can control from a Stamp with serial commands.
Is a DC or AC encoder (controller or whatever it is called?) similar?
Presently I'm using a home made encoder- a metal disk with holes drilled in
it. I count the state changes from a IR photo transistor pair with + - a
millimeter of accuracy using a SX Stamp. It's about the best the Stamp will
do at the speed I'm running. I have to use an external controller. The AC
motor sounds really interesting. I need about 300 inch ounces of torque or
better; the load varies.
Thanks,
Greg Roth
Original Message
From: <cnc002@a...>
To: <basicstamps@egroups.com>
Sent: Sunday, September 03, 2000 7:37 AM
Subject: Re: [noparse][[/noparse]basicstamps] Stepper vrs. DC Motor control
> Greg:
>
> For starters the don't do the same thing. Steppers usually do NOT measure
> but simply take a pulse and direction command from a driver and go, no
> encoder feedback to keep up with the position and no feedback to keep up
with
> the proper speed. DC servo motors on the other hand (or AC servos now)
have
> some type of position feedback device such as an encoder and usually a
tach
> feedback. The encoder keeps track of position which is fed back to the
> controller and checked against the command given. The tach generates a
> voltage based on the speed of the motor and this is fed back to the servo
amp
> where the speed is adjusted based on the PWM or analog voltage signal
given
> the amp. Also DC or AC servos are MUCH smoother than steppers. When
using
> them on machines such as mills or routers the steppers tend to leave
minute
> "chatter" where the actually stop and the start again at the end of each
> "step". Servos do not have this problem as they are a smooth and
continuous
> motion.
>
> On the other hand, steppers are cheaper because they don't have these
> features.
>
> Hope this helps.
>
> Randy A.
>
>
>
that drives brushed DC motors via step and direction signals. I am currently
playing with a few of the beta units. My first testing when I got them was
driving them a PIC. The drivers handle interpreting the encoder and all the
motor control functions and all you do is send a pulse for each step and
pull the direction line high or low to vary the direction. Only takes 2 pins
on the PIC or stamp. The drivers are can handle 24 - 80v at up to 20 amps.
They will cost about $100 per axis. I now have them hooked to my Shoptask 3
in 1 machine and they are 1000 times better than the steppers. They are made
by Geckodrive and can be found on the web at http://www.geckodrive.com/g320/
Tim
[noparse][[/noparse]Denver, CO]
> Thank you everyone for the good information.
>
> One more question: The controller one would use for a DC or AC motor
> encoder, how would you read and command that from a Stamp? I've seen
> stepper controllers that one can control from a Stamp with serial
> commands.
> Is a DC or AC encoder (controller or whatever it is called?) similar?
> Presently I'm using a home made encoder- a metal disk with holes
> drilled in
> it. I count the state changes from a IR photo transistor pair with + - a
> millimeter of accuracy using a SX Stamp. It's about the best the
> Stamp will
> do at the speed I'm running. I have to use an external
> controller. The AC
> motor sounds really interesting. I need about 300 inch ounces of
> torque or
> better; the load varies.
>
> Thanks,
> Greg Roth
>