Stepper Position Feedback

Hello
Iam working on a small project at my school, where Iam building a digital control system using a stepper motor. My buget for this project is between 50 to 80 dollars. THe equipment I have at school is NI Elvis II with a built in DAQ board, LABVIEW Software and it is not equipped with any motion control software anything.I have labview program that allows user to enter the position and direction of the stepper and it has a vi that keeps track of the pulses being sent to the stepper. However I need to know how can I measure the position of the stepper so that i can make sure that it is not missing any steps. Iam using a breadboard to build all the circuitry, I see that the quadrature encoders are expensive, so what other sensors I can possibly use to measure the actuall position of the stepper motor.

You can just make a disk or find something that works for you. I have seen CDs used for this - the small ones that device manufactureres sometimes use to ship drivers on. Chances are that the hole in the CD is bigger than the motor shaft. You could use a hole saw to cut a piece from another CD and use the drilled out piece as a washer. Just look around and use your imagination. You can do this for less than ten dollars.
As for mounting the LED and sensor you just need to build some kind of bracket. I can't help with that without seeing your setup.
=====================
LabVIEW 2012

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The PID controller is still enabled when running the motor in
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Best regards,
Jochen Klier
National Instruments Germany

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So I then emailed the seller, and asked him what he would suggest as a solution. He then offered me a 30% refund. My response was "Sure! for a neutral feedback and three stars!" He then asked if he gave me a refund, or sent me a replacement, would I give him a positive review? Although I don't think that feedback should have been mentioned at all, I'm not sure if ebay would rule that the buyer was using feedback extortion if the conversation happened as reported. The buyer was responding to the sellers offer of a partial refund, they weren't specifically attempting to force the seller to provide: Goods or services that weren't included in the original item's description or purchase price.A return, refund, or replacement item. If the buyer said they wanted a full refund or a replacement without returning an item then that would definitely be feedback extortion. The seller did break the feedback extortion policy when they asked the buyer if they would give a positive review for a replacement or refund. The seller can't require a buyer to leave positive Feedback, specific detailed seller ratings, or revise existing Feedback in exchange for a number of things, including, but not limited to:Receiving the purchased itemIssuing a full or partial refundMonetary compensationAdditional itemsOther goods and services not included in the original listing

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I want to tune my servo motor (voice coil) manually in MAX. Stable step response is possible, but two problems occure:
1) When the step is done, the curve displayed on the "Calibration>Servo tune>Step response" tab shows an excitation step line from -70000 to the value I entered under "step length", although I reset the current position in the "1-D interactive" to zero beforehand.
2) No matter how I change the "step length" value or Ki, the motor step always goes from this above mentioned -70000 to +50000.
To facilitate any hint, mazbe this causes the problems: My encoder head is mounted the way that it gives back negative count values in the positive motor direction. Does this have to be changed or is it possible to also tune the servo with this negative encoder position feedback. Is it even possible the position feedback from - to + within MAX?
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Customer solved the problem:
"Sehr geehrter Herr Wagner,
bzgl meiner Anfrage für die Regelung meines "Vertikal-Servos" habe ich
meine Probleme lösen können:
- Das Vorzeichen der Encoder-Counts konnte ich durch vertauschen der
Encoder-A-B-Polaritäts-Kabel am Encodereingang des Motor Drives umdrehen.
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PID-Einstellungen zu finden, die meine Achse auch mit dem aufliegenden
Gewicht vertikal kontrollieren lassen.
Ihnen nochmals vielen Dank für Ihre Unterstützung.... Die nächsten
Probleme kommen für mich bestimmt.
Freundliche Grüsse,
Henri Hagenmüller"

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I don't believe I'm circumventing any DRM/Copyright. I'm currently enrolled in a Harvard eDx Copyright Law class. As long as you are original and offer a minimum of creativity, you are eligable for a copyright, without any need for registration. But that's besides the point. I can see how it may have flagged the post though.
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Hello,
I am developing a position control system to move a linear stage back and forth using a stepper motor (file 1). The stage will ultimately need to follow the motion path set out in a function that I have defined (file 2).
I have been able to get the motor to move using a Big Easy Driver from Sparkfun (file 3), sending it a PWM signal from one myRIO pin, and setting another pin on the myRIO to high or low in order to establish the direction. From what I understand, each low-to-high transition in the PWM signal causes the motor to take one step (or microstep). Therefore the PWM frequency is equal to steps/second, the motor speed. Using timed loops along with this information, I am able to control how many rotations the motor performs at a constant speed.
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Best,
E
Attachments:
Stepper_PK244-02AA.pdf ‏764 KB
PositionFunction.png ‏133 KB
BigEasyDriver_A4988.pdf ‏383 KB

Hi E,
How are you implementing PWM with the myRIO? Are you just using the myRIO express VI or are you writing your own code?
Also, just as a heads up, the Academic Hardawre Products page is a little more specific to the myRIO and is monitored by NI Developers who work with that device. If you post this question there, you may get a better response.
Ryan K.

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Hello frumple
Please private message the forum admin and he will be glad to help you out.

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Thank you Nathan for this interesting story. :)

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Stepper Position Feedback

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