Question on 3 wire stepper motors.
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Posts: 46,084
I've not been able to find any info on this type of stepper. Most
commonly seen in old drives. Could someone post a quick explaination
on how these drives work?
Thanks
Atomix
commonly seen in old drives. Could someone post a quick explaination
on how these drives work?
Thanks
Atomix
Comments
synchronous motors your talking about. These motors today have 5 or 7
coils and use fancy synchronous motor controllers. These motors are
common in hard disk drives nowadays.
www.didel.com has some basic Stamp code examples for actuating these
motors. You can scale it up using more powerful driver half-bridge
circuits. Go to their Documentation section to see their info about
them.
Basically, you have three wires. You alternately pulse each pair in a
pattern so that it causes the motor to rotate. The pattern can overlap
to achieve higher speeds too. You have to use a half bridge transistor
circuit as one wire is driven high and the other wire is driven low at
the sametime.
Original Message
From: Atomic Nixon [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=-jn9GzTGmC9Ksfb_2eirOTW1EBzdsuDxGxdR6wXcNteEiO7rowMWCaEimZyRZRYNyAYTOi2xCZTQL8qVqQGD]atomicnixon@h...[/url
Sent: Saturday, October 18, 2003 3:14 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] Question on 3 wire stepper motors.
I've not been able to find any info on this type of stepper. Most
commonly seen in old drives. Could someone post a quick explaination
on how these drives work?
Thanks
Atomix
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>I've not been able to find any info on this type of stepper. Most
>commonly seen in old drives. Could someone post a quick explaination
>on how these drives work?
>
>Thanks
>
>Atomix
Atomix -
Is this a motor from a floppy drive, or a hard disk ? If it's from a hard
disk,
it may be a 3 phase motor, and you'll have to find an appropriate driver chip.
If there is a nameplate on it, the information from that may be helpful as
well.
Also, what type of computer was it removed from ?
Regards,
Bruce Bates
a hard
> disk,
> it may be a 3 phase motor, and you'll have to find an appropriate
driver chip.
> If there is a nameplate on it, the information from that may be
helpful as
> well.
> Also, what type of computer was it removed from ?
These motors were from older HD's, 40 to 120 meg range (and whatcha
gonna do with a drive that size eh?). They have three wires, Red,
Black, Green. It seems three-wire steppers are an anomaly... Euch!
By the way, how useful do you think THIS post is -->
http://www.eio.com/public/stepper/0358.html
Euch! Buddy! Could you possibly post ONE sentence on each wire?
That would be three sentences... <sigh> Whadda yutz!
So, these things are described as AC steppers... Hurm... been trying
a couple o variations on how it could work. Eg: Neg on one wire, Pos
on other wire, AC signal on third. I just hate the fact that there's
NOTHING online on these suckers. Oh, and nothing turns up as far as
searches are concerned, numbers/codes on the motor.
Here's another one for those who know motors.... For figuring power
draw... since it's a DC device, can you measure the resistance over a
set of coils and use that to calculate amps drawn?
Atomix
<earlwbollinger@c...> wrote:
> The little Switek synchronous motors are three wire steppers like
the
> synchronous motors your talking about. These motors today have 5 or
7
> coils and use fancy synchronous motor controllers. These motors are
> common in hard disk drives nowadays.
> www.didel.com has some basic Stamp code examples for actuating these
> motors. You can scale it up using more powerful driver half-bridge
> circuits. Go to their Documentation section to see their info about
> them.
> Basically, you have three wires. You alternately pulse each pair in
a
> pattern so that it causes the motor to rotate. The pattern can
overlap
> to achieve higher speeds too. You have to use a half bridge
transistor
> circuit as one wire is driven high and the other wire is driven low
at
> the sametime.
Hey!!! Thanks loads! I belive the document yer talking about is
this one --->
http://www.didel.com/picg/doc/DopiSmoo.pdf
Should be able to get it working now. Thanks.
Here's another one on steppers... I'm using ULN2003's I scavenged
from this digital display unit. Ran across this circuit which should
double the number of motors I can control off the pic. Only needs
two inputs. For some reason I can't get this sucker working, anyone
know what I should be looking for?
http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html
The diagram I'm talking about is about 1/3 of the way down and shows
outputs from the 2003 being used to invert a couple of other pins.
What's the limiting factors for drive speed? Would smoothing out the
pulses (more sine, less square) give more speed? How the hell do
they get these things running so fast?
Atomicat
wrote:
> > Is this a motor from a floppy drive, or a hard disk ? If it's
from
> a hard
> > disk,
> > it may be a 3 phase motor, and you'll have to find an appropriate
> driver chip.
> > If there is a nameplate on it, the information from that may be
> helpful as
> > well.
> > Also, what type of computer was it removed from ?
>
>
> These motors were from older HD's, 40 to 120 meg range (and whatcha
> gonna do with a drive that size eh?). They have three wires, Red,
> Black, Green. It seems three-wire steppers are an anomaly...
Euch!
> By the way, how useful do you think THIS post is -->
>
> http://www.eio.com/public/stepper/0358.html
>
> Euch! Buddy! Could you possibly post ONE sentence on each wire?
> That would be three sentences... <sigh> Whadda yutz!
>
> So, these things are described as AC steppers... Hurm... been
trying
> a couple o variations on how it could work. Eg: Neg on one wire,
Pos
> on other wire, AC signal on third. I just hate the fact that
there's
> NOTHING online on these suckers. Oh, and nothing turns up as far
as
> searches are concerned, numbers/codes on the motor.
>
> Here's another one for those who know motors.... For figuring
power
> draw... since it's a DC device, can you measure the resistance over
a
> set of coils and use that to calculate amps drawn?
>
> Atomix
I'll be happy to offer more incomplete answers.
I'm of a mind that you really have a servo motor (the one that spins
the disk as opposed to the one that moves the arms) and that it is
just a simple DC motor with feedback for speed so the contorller can
regulate the speed.
but, generically speaking, you can ohm the coil and then using the
manufactures recomended voltage, calculate the current.
no manufactures recomended voltage ? check to see if the origional
driving circuit has limiting resistors and what the voltage was.
trashed the old boards ? shame on you, you also tossed a working
drive circit and clues to how it was wired....but all is not lost.
the motor wires will lead you down a path that might work. wire size
of the coils cannot be less than the current carrying of the coils.
ergo you can take a wild guess at the motor current based on the coil
wire size. I'd say to de-rate by 50% to start, but you might be
able to get up to about 100% of the current in that coil. remember
steppers are pulsed so may be able to handle higher amps in pulses.
one method is to run the motor till it gets warm. that is a sign it
is near the limit..... most of the time. A larger stepper is often
rated for 85degC which is HOT to you and me.
did you ohm out the motor ? did you include the case as a possible
4th connection ?
Like I said, more incomplete stuff.
Dave
as you have to create 1/2 of an H-Hbridge (half bridge) A n-channel and
a p-channel MOSFET. Usually everyone uses square waves with MOSFETS as
you want the on/off transition time to go through the analog range as
fast as possible to limit heat buildup. MOSFETS are good at that. The
problem with the darlingtons is they are all NPN thus you either have
them all on or all off but not one on and one off.
What you have to do is drive one motor wire both high and low
alternately, and do this for all three motor wires in sequence. With the
darlingtons (ULN2003) you can't do this properly. You can use either NPN
and PNP transistors or N-channel and P-channel mosfets to make up
half-bridges.
If you study the internals of the PIC micro chips in the Didel.com
articles, you'll see that the I/O ports are all MOSFET half-bridges
which work Ok for the tiiny motors they are driving. For you to increase
the power, you need to hook a PNP and a NPN transistor up to an I/O pin,
so that when the Pin is low one transistor is On while the other is off
and vice versa.
The other thing is you have to start up the motor slowly at low speed
RPM. Then ramp up the speed by increasing the pulse rate slowly. If you
go too fast the motor sits there and vibrates and stops rotating.
Usually they drive current more than voltage through the motors. As they
want a strong electromagnetic pulse to get the rotor spinning. Once you
get the motor up to speed you can reduce the drive current as you only
need to maintain the speed steady at that point. As the speed increases
they change the pulse rate and width and overlap as needed to match the
motor to get it spinning at a good clip.
The hard disk motors spin up to about 3600 RPM or so, depending on the
hard drive model, new ones can run 10,000 rpm or better.
The next thing is these are really low torque motors, so don't expect a
lot of power from them.
They use a special synchronous motor controller IC that has all these
things built in, so the IC chip controls the motor and ramps up the
speed et cetera automatically. Unfortunately these chips seem to have no
documentation on them at all. R at least all the ones I looked at don't.
Mostly Hitachi chips, they all seem to have part numbers thatdon't match
up with anything that I have found.
Hey!!! Thanks loads! I belive the document yer talking about is
this one --->
http://www.didel.com/picg/doc/DopiSmoo.pdf
Should be able to get it working now. Thanks.
Here's another one on steppers... I'm using ULN2003's I scavenged
from this digital display unit. Ran across this circuit which should
double the number of motors I can control off the pic. Only needs
two inputs. For some reason I can't get this sucker working, anyone
know what I should be looking for?
http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html
The diagram I'm talking about is about 1/3 of the way down and shows
outputs from the 2003 being used to invert a couple of other pins.
What's the limiting factors for drive speed? Would smoothing out the
pulses (more sine, less square) give more speed? How the hell do
they get these things running so fast?
Atomicat
> from this digital display unit. Ran across this circuit which
should
> double the number of motors I can control off the pic. Only needs
> two inputs. For some reason I can't get this sucker working,
anyone
> know what I should be looking for?
> http://www.doc.ic.ac.uk/~ih/doc/stepper/control2/connect.html
> The diagram I'm talking about is about 1/3 of the way down and
shows
> outputs from the 2003 being used to invert a couple of other pins.
> What's the limiting factors for drive speed? Would smoothing out
the
> pulses (more sine, less square) give more speed? How the hell do
> they get these things running so fast?
> Atomicat
The step ON pulse needs to be set for the time it takes for each
componet to react, but some overhead. if it takes the Stamp 1uS to
reach a 5V output, then the darlington another 1uS, you need to have
a minimum of 2uS 'ON' time, and doubling that would not hurt. once
you get into the longer response times, you can reduce the overhead
to just a little more.
OF course you need to find out if the switching in on the rising edge
or trailing edge for each component to really contorl what is needed
for each chip.
Then speed of a stepper is based on how fast you can charge the coils
in the motor. remember it is an inductive load.
The higher the voltage, the faster you can deliver the amps, but #1
you must limit the amps with a chopper if you want really high
performances.
To get fast outputs you can just pulse fast.
A note on steppers is that they have more power at low RPM's and get
very weak in the high rpms. very weak.
if you find you are not getting a high top end, but rather stall
abruptly, but have gravel digging starting power, you can gear up the
motor so make it run slower with a faster gear ratio.
Dave