OzEclipse
26-02-2013, 06:51 PM
Hi all,
From time to time people on this forum ask about stepper motor driver circuits for ATM.
Some colleagues at work and I began talking about stepper motors and discovered that we all have different projects with similar requirements so we joined forces and have recently been experimenting with various driver circuits. We've settled on this driver circuit which we are really impressed with and we intend to apply to a variety of automation projects at work and home.
http://www.ebay.com.au/itm/281014472376?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649
Cost $9.50
The board is tiny, approx dimensions are 1.5 x 2cm and comes fully assembled. It does need an independent clock pulse input. You choose a quartz PLL type clock if you need that level of precision or a 555 type circuit (see below) if you can accept a lower precision.
The driver can micro step in Full-step, Half-step, Quarter-step, Eighth-step, and Sixteenth-step increments all easily switchable by configuring switches. Run at 1/16 steps for tracking, switch in 1/8 steps for guiding, full steps for slewing.
The output current is adjustable to minimize power consumption or more precisely optimize power consumption and stall torque.
Manufacturers blurb
This product is a carrier board or breakout board for Allegro's A4988 DMOS Microstepping Driver with Translator and Overcurrent Protection; we therefore recommend careful reading of the A4988 datasheet before using this product.
The translator is the key to the easy implementation of the A4988. Simply inputting one pulse on the STEP input drives the motor one microstep. There are no phasesequence tables, high frequency control lines, or complex interfaces to program.The A4988 interface is an ideal fit for applications where a complex microprocessor isunavailable or is overburdened.
Features:
1. Muximum output current is 1A
2. Short-to-ground and shorted-load protection
3. Adjustable current control
4. Intelligent chopping control
5. Over-temperature thermal shutdown
6. Under-voltage lockout
7. Crossover-current protection
8. Simple step and direction control interface
9. Full-step, Half-step, Quarter-step, Eighth-step, and Sixteenth-step
Clock Pulse Generator
If you don't want to wire up your own clock, this one can be purchased for under $3.50
http://www.ebay.com.au/itm/310565377052?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649
You may need to replace the potentiometer to get the frequency range desired. - easy job!
555 based circuits can be fitted with polyester capacitors and low temperature coefficient metal film resistors to minimise thermal frequency drift.
Stepper motor with integral gearbox
We have also found the following very cheap stepper motor with integral gearbox. I bought 3 for $6.30.
http://www.ebay.com.au/itm/350554126227?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649
This motor has 64 steps per revolution (5.625 degrees per step)
The gear box is 64:1.
Therefore at the gearbox output shaft, it has
5.27 arc mins per step (full step)
0.329 arc mins per step (1/16 step)
It has plenty of torque but the gearbox suffers from about 6 degrees of backlash at the output of the gearbox shaft which might cause some problems in certain applications. But then what can you expect for three dollars? I suspect this motor and gearbox would be fine for a double arm barn door drive where the drive is always pushing in the same direction but no good for a dec drive on a DIY equatorial mount for astrophotography where the backlash would drive you nuts.
In one application, we are fitting it as the drive motor to an old shop bought equatorial mount for one of my colleagues who just wants a cheap drive to keep the object in the eyepiece of a 6 inch reflector while his kids look through it. The mount is old and isn't a standard EQ1,2,3 etc so we can't find a standard motor to fit it. The gear ratios would be all wrong. Another colleague wants to build a barn door drive for wide field astro photography. In the workplace, one of my colleagues wants to use it to actuate some valves in a process control project for a scientific instrument.
For astrophotographic and other precision applications, I recommend that you spend the money on a high precision gear box and motor to suit however the driver board might still be the ticket.
Regards
Joe Cali
From time to time people on this forum ask about stepper motor driver circuits for ATM.
Some colleagues at work and I began talking about stepper motors and discovered that we all have different projects with similar requirements so we joined forces and have recently been experimenting with various driver circuits. We've settled on this driver circuit which we are really impressed with and we intend to apply to a variety of automation projects at work and home.
http://www.ebay.com.au/itm/281014472376?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649
Cost $9.50
The board is tiny, approx dimensions are 1.5 x 2cm and comes fully assembled. It does need an independent clock pulse input. You choose a quartz PLL type clock if you need that level of precision or a 555 type circuit (see below) if you can accept a lower precision.
The driver can micro step in Full-step, Half-step, Quarter-step, Eighth-step, and Sixteenth-step increments all easily switchable by configuring switches. Run at 1/16 steps for tracking, switch in 1/8 steps for guiding, full steps for slewing.
The output current is adjustable to minimize power consumption or more precisely optimize power consumption and stall torque.
Manufacturers blurb
This product is a carrier board or breakout board for Allegro's A4988 DMOS Microstepping Driver with Translator and Overcurrent Protection; we therefore recommend careful reading of the A4988 datasheet before using this product.
The translator is the key to the easy implementation of the A4988. Simply inputting one pulse on the STEP input drives the motor one microstep. There are no phasesequence tables, high frequency control lines, or complex interfaces to program.The A4988 interface is an ideal fit for applications where a complex microprocessor isunavailable or is overburdened.
Features:
1. Muximum output current is 1A
2. Short-to-ground and shorted-load protection
3. Adjustable current control
4. Intelligent chopping control
5. Over-temperature thermal shutdown
6. Under-voltage lockout
7. Crossover-current protection
8. Simple step and direction control interface
9. Full-step, Half-step, Quarter-step, Eighth-step, and Sixteenth-step
Clock Pulse Generator
If you don't want to wire up your own clock, this one can be purchased for under $3.50
http://www.ebay.com.au/itm/310565377052?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649
You may need to replace the potentiometer to get the frequency range desired. - easy job!
555 based circuits can be fitted with polyester capacitors and low temperature coefficient metal film resistors to minimise thermal frequency drift.
Stepper motor with integral gearbox
We have also found the following very cheap stepper motor with integral gearbox. I bought 3 for $6.30.
http://www.ebay.com.au/itm/350554126227?ssPageName=STRK:MEWNX: IT&_trksid=p3984.m1497.l2649
This motor has 64 steps per revolution (5.625 degrees per step)
The gear box is 64:1.
Therefore at the gearbox output shaft, it has
5.27 arc mins per step (full step)
0.329 arc mins per step (1/16 step)
It has plenty of torque but the gearbox suffers from about 6 degrees of backlash at the output of the gearbox shaft which might cause some problems in certain applications. But then what can you expect for three dollars? I suspect this motor and gearbox would be fine for a double arm barn door drive where the drive is always pushing in the same direction but no good for a dec drive on a DIY equatorial mount for astrophotography where the backlash would drive you nuts.
In one application, we are fitting it as the drive motor to an old shop bought equatorial mount for one of my colleagues who just wants a cheap drive to keep the object in the eyepiece of a 6 inch reflector while his kids look through it. The mount is old and isn't a standard EQ1,2,3 etc so we can't find a standard motor to fit it. The gear ratios would be all wrong. Another colleague wants to build a barn door drive for wide field astro photography. In the workplace, one of my colleagues wants to use it to actuate some valves in a process control project for a scientific instrument.
For astrophotographic and other precision applications, I recommend that you spend the money on a high precision gear box and motor to suit however the driver board might still be the ticket.
Regards
Joe Cali