Newbie: stepper motor

[Elijah Bailey]

I want to buy a stepper motor that I could control using my
AD/DA card? parallel/serial port? I would like to have a sensor
on it that could tell me if it slipped. And of course I would
like to control it using a computer.

Does anyone know of a cheap solution. I'm planning to put
one or two pound load on it, and would like it to accelerate
and decelerate fast.

Any pointers?

Thanks,
--Elijah

 

[Roger Hamlett]

"Elijah Bailey" <geomrock@hotmail.com> wrote in message
news:e008fef8.0404020730.417a92ab@posting.google.com...

I want to buy a stepper motor that I could control using my
AD/DA card? parallel/serial port? I would like to have a sensor
on it that could tell me if it slipped. And of course I would
like to control it using a computer.

Does anyone know of a cheap solution. I'm planning to put
one or two pound load on it, and would like it to accelerate
and decelerate fast.

Any pointers?

Thanks,
Look at:

http://www.doc.ic.ac.uk/~ih/doc/stepper/
You only need to add a once/rev pulse sensor, and connect this to a bit of
the parallel input to give an indication it has slipped, when you get to
this point. A more complex indication (with a shaft encoder), is more
expensive/complex than the motor drive.
Speed is largely down to how you drive the motor. You will need to use some
form of 'overvoltage' driving, either with a current controlled driver chip,
or a dropper resistor. Typically something like a 60v supply is used on the
units controlling devices like small milling machines. The code you use will
also need to ramp the step rate for best acceleration/deceleration
behaviour. A 'one or two pound load', means nothing, unless you say what
speed you expect to get it to, and the moment arm involved.
The 'best' solution (and probably the cheapest!), would be to do a web
search on CNC adaption kits for milling machines/lathes.

Best Wishes

 

[John Jardine]

Elijah Bailey <geomrock@hotmail.com> wrote in message
news:e008fef8.0404020730.417a92ab@posting.google.com...

I want to buy a stepper motor that I could control using my
AD/DA card? parallel/serial port? I would like to have a sensor
on it that could tell me if it slipped. And of course I would
like to control it using a computer.

Does anyone know of a cheap solution. I'm planning to put
one or two pound load on it, and would like it to accelerate
and decelerate fast.

Any pointers?

Thanks,
--Elijah
For 'cheap' you'll have to do it yourself.

If bought new then the motor's going to be the most expensive part. The size
"23" motors can give at low speeds say 4 pounds of turning force on a 1"
pulley or timing gear but can cost the equiv' of $50 or more. For
experimental purposes buy surplus or scrap motors (they rarely wear out).
Look out for 5 or 6 or 8 lead motors. The 'bipolar' 4 wire types are pigs to
electronically control.
Build the motor driver from one of the numerous designs or kits available on
the web. (look for something like 'unipolar stepper driver' or 'bi-level
driver'). These are basically a few power FETs or darlington transistors
that connect to the motor windings. Use a high as supply voltage as the
driver circuit will allow.
For simplicity in both programming and hardware (and faultfinding), control
the motor electronics using 4 pins from the parallel port. Read the slip
sensor via the parallel port. This port has enough pins to also drive a
second motor and limit switches etc.
Be aware that stepper motors have hard physical limits as to how fast they
can be accel/decelled before losing steps. Be prepared to spend time on
optimising the software to 'tune' the final arrangement.
regards
john