Question

I have a question (not surprisingly) about the stepper motor that comes in the chipKIT Starter Kit (28BYJ48A). 

 

I know that I'm supposed to pulse the four lines to make the electromagnets "turn on" in such a way to make the motor turn one way or the other.  

 

I did so by driving various I/O pins on the chipKIT uC32 high and low and got it to rotate, but it seems I can only get it to rotate up to a maximum speed of ~12 revolutions/min, since any shorter delay than 3 ms between driving the magnets high/low seems to make the electromagnets shift around faster than the motor can keep up.

 

My other question (which I'm honestly more curious about) is what the 5th wire for on the header for the stepper motor? According to this website, that wire should be hooked up to a 5V line, but when I hook that line up to 5V (or 3.3V or ground) the motor shaft stops rotating; I'm only getting it to rotate when that 5th line (the red one) is floating. So... should I be seeing this?

 

Thanks,

James

 

P.S. How would I hook up this 5 pin header to the PmodSTEP? The PmodSTEP only has 4 and 6 pin headers so the 5-pin header from the stepper motor physically doesn't fit.

Share this post


Link to post
Share on other sites

5 answers to this question

Recommended Posts

  • 0

After doing a bit of research, I found out what the 5th wire (the red one), could be used for. 

 

The Stepper motor claims it needs to use 5V, so if you hooked up the stepper motor inputs to a Darlington Transistor array, when you drive a particular input HIGH on the microcontroller, the Darilington Transistor will bring that particular output to a LOW state, which will encourage current to be drawn.

 

Since stepper motors work by electromagnets, when we are driving a particular magnet low, this means that the rotating motor shaft itself will need to be at a HIGH state so that it is a "magnetic opposite" to the "on" electromagnet.  Basically, this means that the 5th wire on the stepper motor will need to be attached to a 5V line in order to have the motor work.  This also gives it a lot more torque than I was seeing before and allowed me to get about 48 revolutions/min.

 

As for connecting to the PmodSTEP, an external connector will need to be used.

 

The PmodSTEP only accounts for the popular 4-wire (a purely bipolar stepper motor) and the universal (bipolar and unipolar) 6-wire stepper motor.  The 5-wire stepper motor in the chipKIT Starter Kit is actually a 6-wire stepper motor; however, the two central taps to the coils are internally tied together to create a 5-wire header.

Share this post


Link to post
Share on other sites
  • 0

Hi ,

I have a question. I tried to connect the motor  ( 5 pins) whereby the red wire was left floating but I was unable to rotate it. The motor was vibrating  meaning that the phase sequence is not good. But I tried to look into the PmodStep schematics but was unable to know about the connection of the remaining 4 wires. Can someone please help me??

Thanks in advance

Share this post


Link to post
Share on other sites
  • 0

Hi,

 

I chatted with you earlier today, but I am putting a condensed reply here as well. If you are using a 5 wire stepper motor that looks like this one in the picture link below:

 

http://www.instructables.com/file/FF7YQ75I0XOISBQ

 

then the way that the wires are arranged are follows:

The orange wire corresponds to coil 1the yellow wire corresponds to coil 2the pink wire corresponds to coil 3the blue wire corresponds to coil 4and the red wire corresponds to the center taps on the two sets of coils.

 

     You can connect the four coils to the pins on the PmodSTEP as well.  If you are connecting to J2 (the four pin connection), I would recommend attaching the orange wire to pin 1, the yellow wire to pin 2, the pink wire to pin 3, and the blue wire to pin 4.  The red wire should be left floating in this case.  These four pins (1, 2, 3, and 4) are associated with the pins 7, 8, 9, and 10, respectively, on the 6x2 pin header.

     To run the stepper motor in this configuration (bipolar mode) you will need some way to get current flowing through the electromagnetic coils in the reverse direction.  This can be done by either having a board that can output both positive and negative voltage signals, or by using an H-Bridge.

 

     Alternatively, you can also connect the 5 pin stepper motor to pin header J3 on the PmodSTEP.  Here, I would recommend attaching the orange wire to pin 1, the yellow wire to pin 2, the pink wire to pin 5, and the blue wire to pin 6.  The red wire can be attached to either pin 3 or pin 4; it does not matter which one you choose.  The pins 1, 2, 5, and 6 on J3 are also associated with the pins 7, 8, 9, and 10, respectively, on the 6x2 pin header.

     To run the stepper motor in this configuration (unipolar mode), all you need is to have your board produce a positive voltage signal and a ground signal; no H-bridge will be required. You can learn how unipolar mode works in principle by following my Instructable here.

 

Please let me know if you have any other questions.

Share this post


Link to post
Share on other sites
  • 0

Hi 

I did the connection a you mentioned above but still, my motor does not rotate. Using an oscilloscope, I checked the output of the Pmodstep with  motor connected and motor not connected. The output is as desired and thus i fail to understand why the motor is not rotating. I checked the frequency and the motor should rotate at about 400Hz.

Share this post


Link to post
Share on other sites
  • 0

Ah. Presuming that your output is performing as desired, then the reason your motor is not rotating is because you are trying to rotate it to quickly.  The fastest that I was ever able to rotate the stepper motor was about 60 rotations per minute or about 1Hz. 

 

You may be able to get the motor to rotate quicker by using a larger voltage signal, but it will get nowhere near the 400Hz that you are wanting. The only way that I know to fix this is to get a new stepper motor that is capable of rotating that quickly.  Unfortunately, I don't personally know of a stepper motor off the top of my head which is capable of that speed; I believe there are motors that can go that quickly, I just don't know which ones can.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this