Stepper vrs. DC Motor control
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Posts: 46,084
At 09:28 AM 9/2/00 -0700, Greg wrote:
>Stepper motor, DC motor with encoder, both can measure and postion. Why
>would someone choose one over the other? For a Stamp project it, seems one
>would be best driving either of them with a off board chip. I invite and
>appreciate any comment.
The problem with most stepper based systems is that without an encoder,
it's not a closed loop (no feedback). If the stepper stalls, your system
has no idea where it is. With an encoder, if a motor stalls (servo or
stepper) you still have position data. Of course, without an encoder, the
logic may not even realize the motor has stalled. Bipolar steppers are
simple to drive and work well in situations with a predictable load. They
can produce highly accurate repeatable moves cheaply, which is why they're
used in so many consumer electronic devices. DC servos with encoders
require more logic to control but offer superior accuracy under variable
loads. Personally, I almost always prefer to use stepper motors with
microcontrollers. As long as your motor has enough power to do the job,
they're cheap, reliable and easy to interface...any surplus store will have
tons of different steppers these days.
Just my 2 cents, Duncan
>Stepper motor, DC motor with encoder, both can measure and postion. Why
>would someone choose one over the other? For a Stamp project it, seems one
>would be best driving either of them with a off board chip. I invite and
>appreciate any comment.
The problem with most stepper based systems is that without an encoder,
it's not a closed loop (no feedback). If the stepper stalls, your system
has no idea where it is. With an encoder, if a motor stalls (servo or
stepper) you still have position data. Of course, without an encoder, the
logic may not even realize the motor has stalled. Bipolar steppers are
simple to drive and work well in situations with a predictable load. They
can produce highly accurate repeatable moves cheaply, which is why they're
used in so many consumer electronic devices. DC servos with encoders
require more logic to control but offer superior accuracy under variable
loads. Personally, I almost always prefer to use stepper motors with
microcontrollers. As long as your motor has enough power to do the job,
they're cheap, reliable and easy to interface...any surplus store will have
tons of different steppers these days.
Just my 2 cents, Duncan
Comments
would someone choose one over the other? For a Stamp project it, seems one
would be best driving either of them with a off board chip. I invite and
appreciate any comment.
Greg Roth
Original Message
From: <orthner@s...>
To: <basicstamps@egroups.com>
Sent: Saturday, September 02, 2000 4:18 AM
Subject: Re: [noparse][[/noparse]basicstamps] DC Motor control
> At 07:25 AM 9/2/00 +0200, you wrote:
>
> > we are searching for a DC motor control to set the position of a
> > linear screw drive.
> > Has anybody done/tried this with BASIC Stamps ?
> >
> > Our screw so far is driven by a Maxon DC Motor RE35 90W (12V) and a
> > HP HEDS 5540 Digital Encoder. A 0.52 volt output / 1000rpm DC tacho
> > is available too.
>
> For driving a DC motor with an encoder an excellent dedicated chip is
> national's LM628/629. This thing is basically a motion control system on a
> chip. You connect the motor and encoder to it, then send it data. It can
be
> set up for position/velocity and does PID on the fly to generate it's own
> trajectory profile. I've never used this with a stamp, but it should be
> possible.
>
> Duncan
>
>
>
stepper motors.
www.microcontrollertricks.cjb.net
I hope the info is of some help.
Gary
Original Message
From: "Greg Lee Roth" <greg_roth@m...>
To: <basicstamps@egroups.com>
Sent: Saturday, September 02, 2000 11:28 AM
Subject: [noparse][[/noparse]basicstamps] Stepper vrs. DC Motor control
> Stepper motor, DC motor with encoder, both can measure and postion. Why
> would someone choose one over the other? For a Stamp project it, seems
one
> would be best driving either of them with a off board chip. I invite and
> appreciate any comment.
>
> Greg Roth
>
Original Message
> From: <orthner@s...>
> To: <basicstamps@egroups.com>
> Sent: Saturday, September 02, 2000 4:18 AM
> Subject: Re: [noparse][[/noparse]basicstamps] DC Motor control
>
>
> > At 07:25 AM 9/2/00 +0200, you wrote:
> >
> > > we are searching for a DC motor control to set the position of a
> > > linear screw drive.
> > > Has anybody done/tried this with BASIC Stamps ?
> > >
> > > Our screw so far is driven by a Maxon DC Motor RE35 90W (12V) and a
> > > HP HEDS 5540 Digital Encoder. A 0.52 volt output / 1000rpm DC tacho
> > > is available too.
> >
> > For driving a DC motor with an encoder an excellent dedicated chip is
> > national's LM628/629. This thing is basically a motion control system on
a
> > chip. You connect the motor and encoder to it, then send it data. It can
> be
> > set up for position/velocity and does PID on the fly to generate it's
own
> > trajectory profile. I've never used this with a stamp, but it should be
> > possible.
> >
> > Duncan
> >
> >
> >
>
>
>
>
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.