LiniStepper v1.

Microstepping Stepper Motor Driver Kit

How to use it -
and keeping it cool!

Also:

• How to blow up the Linistep (or avoid doing so) Hint: It isn't easy to destroy and even then, repair is cheap...
• Linear stepping with the Linistepper or How smooth is smooth?

CAUTION: The Linistepper requires suitable, large heatsinking. Such as standard chunky aluminum/alloy heatsinks with fins. For additional heat dissipation use a bigger heatsink with extra fins, or even add a small computer fan to remove the excess heat. (steel is not a suitable heatsink, the angle bracket is NOT a heatsink.)

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Connecting the Linistepper.
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Control Connector

The connector furthest from the heatsink (on the left) is the control
connector.

Starting closest to the diodes, the 7 pins are:

* ground           (also attached to the motor ground)
* +5v regulated    (power for PIC chip)

* step input       (new step on + going edge)
* direction input  (hi = reverse)
* low power        (lo = low power)

* mode 0
* mode 1  (these select the stepping mode as shown in this table)

mode 1   mode 0    result
0        0         200   (full step)
0        1         400   (high-torque half step)
1        0         1200  (microstep 6th)
1        1         3600  (microstep 18th)

The mode 1 pin is at the corner of the printed circuit board.

For information on how to connect the Linistepper (or multiple
Linisteppers) to a PC parallel port, see:
http://www.piclist.com/io/stepper/linistep/faq.htm#37570.4504050926
or try our Linistepper "4 AXIS / Mode / 555 / PWR" kit
------------------------------------------------------------------------

Power and Motor Connector

The connector closest to the heatsink is the power and motor connector.
The 7 pins are divided into 2 for the power connector,
and 5 for the motor, starting closest to the resistors;

Power
* main ground
* + main voltage (+4v to +35v)

Motor
* motor + (unipolar motor common)
* phase A+
* phase A-
* phase B+
* phase B-

Don't disconnect any motor wires with the power turned on!

------------------------------------------------------------------------
Using the Linistepper
------------------------------------------------------------------------

Important!
All 5 input pins MUST be connected to something, ie to a digital
output or tied to 0v or +5v. DO NOT leave inputs floating!

Most of this is quite obvious, each time the step input is clocked
from lo to hi (from 0v to 5v) the motor will turn one step.

The direction will be forward, unless the direction input is hi.

The low power input should be hi to get full power, lo will give low
power "wait" mode.

Set the 2 mode inputs to give the desired stepping mode.

------------------------------------------------------------------------
Motor does not turn?? 
------------------------------------------------------------------------

First check that the regulated +5v is there, then motor voltage which
is normally between 4v and 35v.

Assuming you are clocking the step input and you have the low power
pin held hi (full power) and you have the motor common + wire connected
properly there is one likely reason that the motor does not turn.

Try swapping one A wire with one B wire, you may have connected the
motor phasing wrong. If you have the phasing wrong, the motor will 
tend to sit there and "wobble" or "buzz". :o)

If the motor turns, but in the wrong direction, you only need to swap
the two A wires with each other.

Don't disconnect any motor wires with the power turned on!

------------------------------------------------------------------------
Keeping it Cool!
------------------------------------------------------------------------


 Jelly Baby Engineers: "Heatsink? You call that a Heatsink??
THAT'S A HEATSINK!!"

The linistepper is a linear driver and will dissipate quite a lot of
heat IF you have a psu voltage that is a lot higher than the motor
coil voltage.

The difference between supply voltage and motor voltage is lost as
wasted heat energy.

When you only need low speed performance, ie motor speeds under
4 revs/second, you can use low supply voltage and minimise heat
and power loss. The motor will perform well at low speeds, with
the linear smoothed microstepping advantages giving better performance
than many chopped drivers that are not microstepped, and similar
heat performance.

To get minimum heating and power loss you need to use the minimum
supply voltage that will give full current with your chosen motor.

Finding the max efficiency point is quite easy:
* make sure low power input is set to full power
* start with psu voltage a few volts higher than the rated motor voltage
* run the motor at a typical speed
* using a variable psu and amp meter;
* slowly reduce the voltage until the amps drop suddenly
* the voltage JUST before the amps drop is the max efficiency (min heat)

In most stepper uses a motor speed of 4 revs/second etc is all you
require, especially when microstepping gives increased positioning
resolution AND increased low speed torque. You no longer need excessive
gearing to get resolution and many apps no longer need high speeds.
Using a psu of only 3v above the motor voltage will give decent motor
performance and greatly reduced motor heating.

If you need better high speed performance you will need to use
a higher psu voltage. How much higher depends on the torque needed at
the highest speeds. Here's a bit of theory about this:



Stepper inductance
Stepper motor coils are magnetic and have inductance. To put this very
simply, inductance means that it takes TIME to build a magnetic field
in the coil, and larger inductance means that the change from no magnetic
field to full magnetic field takes longer than a low inductance motor.
Inductance is closely related to how many turns of wire so motors that
have finer wire and more turns will have higher inductances.

Like this:
fine wire = high volts/low amps = high inductance = slow motor
thick wire = low volts/high amps = low inductance = fast motor

Many people instantly assume that low inductance motors are better,
and indeed these days they are more common with new motors. But low
inductance motors are NOT always the best choice.

The linistepper was designed to be well suited to many older stepper
motors, most of which are high inductance. These motors are often found
at VERY CHEAP prices from "surplus" sellers.

Apart from that big advantage, high inductance motors are usually
more efficient magnetically and often give higher holding torque for
the same coil wattage. These charts are from a manufacturers website.
Motors are the same apart from winding type. Holding torque is 20%
more for the high inductance motor, and even at 400 steps/sec
(2 revs/sec) the high inductance motor still has 8% more torque than
the "fast" motor.



The best advantage of high inductance motors is that because of
their inability to change current rapidly they are a better choice
when you mainly need low speeds. They are smoother and produce less
excitation energy at low speeds as they change from step to step more
gently. I often see people struggling with resonance problems, and find
they are using low inductance motors on systems that never exceed a
few revs/second! Many of the suppliers are at fault here, and even the
educational institutions often teach that low inductance motors and
chopper drives are "superior". Superiority MUST be evaluated by
application. :o)

In any case for the linistepper (or any linear driver) it is better to
use the higher impedance motors, simply because they require less current.

The amount of PSU voltage you need is determined by the application.
In most cases a voltage of 3x the rated motor voltage will give
decent performance through the main resonances up to 10 or 15 revs/second.
I have one machine here with 5v 1A motors giiving good power at speeds
up to 10 revs/second, and an 18v PSU. I also ran an old low-speed
"pancake" type 5v 400mA motor at a speed of 80 revs/second with the
linistepper and 25v psu... It screamed!

Increasing the PSU voltage increases the torque at high speeds, but
also increases heat and power waste. You will get better overall
performance by choosing a motor with lower current and higher inductance.
However if your application really does need high torque at very
high speeds you will need a chopper drive and low inductance motor.

Important!
Only use higher PSU voltage if you REALLY need high speed power.
In most cases the problems users experience relate to resonance at
lower speeds. Low speed resonance is reduced by using a lower PSU
voltage!

On a system where low speed resonance is a problem (like a belt driven
setup or any lightweight system) you will find resonance is greatly
reduced by using the lowest possible PSU voltage, where the motor
inductance is maximised in effect. This gives the smoothest possible
step transitions, and slow resonant systems are one situation where a
correctly set up linear and "old fashioned" high inductance motor will
really out-perform the modern chopper driver.

Here are two charts showing typical motor resonances, these are fairly
typical high inductance motors and show how resonance is generally not
a problem after about 2 revs/second. With low inductance motors you
may still be having bad resonance problems even as high as 20 revs/
second.




Running your system with a variable voltage psu and testing for motor
speed and resonances you can determine the optimum psu voltage where
smoothest operation and less heat (low psu voltage) is obtained at a
psu voltage high enough to still give the desired torque at higher
speeds.

Tips for cool running!
* use the lowest PSU voltage possible
* use a large heatsink
* use fan cooling (3 inch PC fans are as cheap as $1 these days)
* fan cooling reduces heatsink size by 3x or 4x
* use a metal case as part of the heatsinking
* test for 1 hour minimum to measure the running temperature
* microstepping modes 1200 and 3600 are cooler than 200 mode
* use the low power mode during all wait periods
* keep transistors UNDER 50 degrees celcius at all times


------------------------------------------------------------------------
Interfacing with CNC software
------------------------------------------------------------------------

The inputs to the linistepper can be connected to a PC printer port,
or other 5v digital device. Be aware that the PC and the stepper motor
PSU and the +5v regulator must all share the same ground. As PC's have
a grounded case and PSU this is rarely a problem.

Some PC printer (parallel) ports only put out 3.5v when at logic 
"high". The linistepper inputs require over 4v input for a logic
high, and under 1v to input a logic low. In some rare cases the PC
printer port will not output >4v and you may need to add 1000 ohm
resistors from each of the input pins to 5v. A simple test with a
voltmeter should confirm that your PC port voltages are within spec.

The linistepper uses a + going step clock. Each step occurs when the
step input goes from 0v to 5v. Set your CNC software for + going step.
Likewise set the direction input to give the correct direction
motor rotation. If you can't change the direction in your CNC software
setup you can swap the two motor A phase wires with each other.


------------------------------------------------------------------------
Changing step modes on the fly!
------------------------------------------------------------------------

The linistepper provides the feature where you can change between step
modes on the fly, ie as the motor is running. This allows you to use
200 or 400 steps for fast transits and then change to 1200 or 3600 steps
for final positioning.

This is an advanced feature and has some drawbacks, the main one is
that your controlling software must be responsible to track the change in
step resolution. I don't suggest using this feature unless you are
sure that you can do this without losing track of the step position.

The basic rule:
Make sure the driver is on a valid microstep for the mode you set,
BEFORE you change to that mode.

ie; if you are in 3600 step mode and you want to change to 1200 step
mode, you must first be on a valid microstep for the 1200 step mode.
These valid steps are every 3rd microstep, so when changing from 3600
mode to 1200 mode you must be on the 0,3,6,9, etc step.

The valid steps for each mode are shown here:
Mode    Valid steps
3600    all 72 microsteps;  0 to 71
1200    every 3rd step (mod 3) steps; 0,3,6,9 up to 69
400     only 8 valid steps;   4, 13, 22, 31, 40, 49, 58, 67
200     only 4 valid steps;   9, 27, 45, 63

So if you are changing from 3600 step mode to 200 step mode, you must
first position the motor on either the 9, 27, 45 or 63 microstep, as
these are the only valid steps for the 200 mode, and THEN you can change
to the 200 step mode.

If you don't position on a valid step before changing mode, the driver
will LOSE or GAIN steps when it re-synchronises in the new mode. This
results in a step error, which is also continued when the mode is changed
back or changed again.

When the linistepper powers up, it is on step 0. The user software is
required to count steps forward and back and always track which of the
72 possible steps the driver is at. If your CNC software can't do this
modulus 72 tracking then don't change modes on the fly!

There are further complications starting in 200 or 400 modes.
If starting in either of these modes, the step will be 0, which is
a non-valid step. The PIC will add 9 or 18 microsteps for each step
signal. The driver will be on invalid steps until the cycle loops.
That will occur in one step if the first step is backward, otherwise
it will take 4 steps forward in 200 mode, or 8 steps forward in 400
mode to re-synchronise onto valid steps.

So, do not change modes on the fly unless;
1. you know how to track and sync the steps, or,
2. you don't care about losing some steps :o)

It is possible to re-write the PIC software to address these issues and
keep track of the step offsets internally, but I really can't be bothered
as the modulus 72 tracking still needs to be done in the OTHER software
(the PC side). :o)

-end

Questions:

• spamedgey01~NOSPAM~ at gmail.com asks:

  As a newbie, I was wondering what values would I need to change R14-17 and R18-29 to allow me to run 5V 3Amps 400 step. Or could I just use 3 X 1ohm 5W res and cool them?

  James Newton replies: See: Tuning the Linistepper for different motors, loads, and current in the section "Changing Current"; there is a little calculator that will tell you exactly what values you can use.+

  +

• asks:

  Hello,
  I have tinkered with running a stepper motor with a pic and found that the timming of pulses had a profound effect on the power of the motor. Using the linistepper will I still need to pay so close attention to the timing of the pules?
  Thanks.

• spamstratomech~NOSPAM~ at centurytel.net asks:

  So if I have a stepper motor marked as 24 volt, 0.3 amp would this be considered a high inductance motor? What kind of performace loss would there be if it was powered by a lower voltage? Would it lose half of its torque? Application would be 1 rpm or less. Is the Linistepper capable of this?
  Thanks,
  Nathan

  That is correct, it would run at half power. The slow motion is not a problem, but depending on the load and the design of the motor, it might slip.
   

• Do I need to connect an extra set of diodes or other protection device to the printer port or does back-current protection already exist within the hardware?
   
  Yes, it is crude but has not ever caused problems that i'm aware of.
   
  You MUST make sure that the linistepper ground 0v (which is shared for motor power and 5v rail) is connected properly to the PC case ground, so that all signals are compatible. To do this requires that the linistepper motor and 5v power are from an isolated source (ie mains transformer etc) which is usually the standard.
   

Comments:

Tuning the Linistepper for different motors, loads, and current. +

  .