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Stepper motor driver for telescope mount - Page 3 — Parallax Forums

Stepper motor driver for telescope mount



  • bbrien,

    Do you the get similar resistances for the 2 coils, and is the coil value the same when you measure the coil in reverse?

    Also, do you have another stepper to rule out your drive circuitry or another driver to rule out your motor?

    Try giving each of the wires of a connector a small tug to make sure they are secure.

  • I read 29.8 + or - .1 ohms
    none of the available drivers work with these steppers.
    wires are secured.
    Circuitry at bottom of post # 42 doesn't seem to work . no output wave forms from "LS74 ' flipflops. please check the circuit and data sheet for set and reset.

  • jmgjmg Posts: 15,155

    @bbrien said:
    Circuitry at bottom of post # 42 doesn't seem to work . no output wave forms from "LS74 ' flipflops. please check the circuit and data sheet for set and reset.

    The second scope image you gave in #45 looked fine, and is what one expects to see for a phased stepper drive ?
    Has that been lost somehow ?

  • @bbrien said:
    I read 29.8 + or - .1 ohms

    There was a reason, I asked for a matrix of the resistances! Please provide it, if you want qualified help!

    Also I hope you did not use the circuit of #42 because in it there is no means to deal with 3V3 logic of P1 in it. This had been discussed before! We need to know exactly, what you are really doing.

    It drives me crazy to see you struggling and have to ask questions, because your communication is too sparce, to be able to help you.

  • I am not sure what you mean by "Matrix of resistances" but here's what I know at this point 29.8 ohms plus or minus.3 ohms and that is measured forward and reversed in both sets of coils. I also have a scope that uses a DC motor on the DEC. axis and a geared stepper on the R.A. axis Which work just fine . They are in Thailand now. On the schematic I will try another4027 chip.

  • In mathematics, a matrix (pl: matrices) is a rectangular array or table of numbers, symbols, or expressions, arranged in rows and columns, which is used to represent a mathematical object or a property of such an object. (wikipedia)
    I had written: Until the parts arrive you could measure resistance between all ! combinations of the leads and also to the motor housing -a matrix- and post them here.

    I give up here.

  • bbrien,

    Create a wiring table like the one of pages 164 and 165 of this PDF.

  • I hope this helps. I am putting aside the schematic with the "SN74HCT157E for the Time being. With the first schematic I have reduced the motor voltage to 6.3 VDC.

    1396 x 2092 - 632K
    2560 x 1920 - 948K
  • @bbrien said:
    I hope this helps. I am putting aside the schematic with the "SN74HCT157E for the Time being. With the first schematic I have reduced the motor voltage to 6.3 VDC.

    Ok, as I had asked for the matrix.
    This looks like a normal unipolar motor with relatively high resistances made for low speeds. The coils seem to be ok. There might still be a mechanical problem or one with the permanent magnets.

    My recommendation is still to get these A4988 modules, which also solve the 3.3V logic interface, and a new step motor following my mini tutorial and get started with these. After you have verified that this works, you can try to switch over to this unknown motor. Or perhaps just use the Polulu motor?
    Good luck!

  • bbrienbbrien Posts: 561
    edited 2023-10-16 21:34

    According to the datasheet, the minimum operating voltage is 8VDC and the max available on my board for my stepper is 6VDC and my test stepper is only5VDC @.25A , and the motor voltage is adjustable. I have used in the past a MP6500 digital and a DRV8834, did not work.(once package opened, nonreturnable).
    PS; I am retired and on social security: wife will not support this hobby. Have also used the "easy driver" and no luck. Will do what I can when I can.

  • Ok, what you also can do to verify the motor is manually apply the sequence of winding currents.
    Where 0 is no current, 1 is forward current and -1 is current in reverse direction. The columns are the two windings.

    Your power supply is verified to be stable and capable to deliver the power?

    For clarity for yourself and for the communication with others it is good or even necessary to have a complete schematic.

  • Building new schematic with Kicad. Replaced CD4027 again set motor voltage at 5.5 and motor now turning but getting spikes and reduced voltage will send picture of waveforms later.

  • bbrien,

    Do you have a L293D?

  • bbrienbbrien Posts: 561
    edited 2023-10-30 06:42

    I have used them before and and found them difficult to work with , it's too bad they don't have a device similar to the mc 3479 anymore. Also The voltage reduction came from the power distribution panel , voltage dropped below 9 VDC and the regulators couldn't supply my needed 9V.

  • bbrien,

    What other motor drivers do you have?

    I asked about the L293D because it should be very simple to use.
    All you need to do is verify that your stepper works properly.

    We don't know if your problem is the motor, the driver, the code, or a combination.
    Testing each item by itself is one way to determine where the problem is.

    If the stepper is working correctly then running through the step sequence should move it in one direction, and running the sequence in reverse should move it in the other direction.
    The faster you run through the sequence, the faster the stepper should move, but there is a limit to how fast the motor will reliably step.

    You could test your stepper with an Arduino if you have an extra one.

  • Does the code use a pulse line and a direction line , that's how my program works. the system seems to be working somewhat, after several seconds the voltage is getting pulled down to about about 3v but the motor keeps running just the wave form changes. could be from the breadboard.

  • bbrien,

    How are you powering your setup because if the voltage is dropping then your circuit is not getting enough current.

    Making a stepper move is very simple and doesn't require a sophisticated driver chip.
    Energize each coil is sequence and it will move Clockwise.
    Reverse the sequence and it will move Counter-Clockwise.
    I suggested the L293D because it's a simple driver chip that feeds the drive signals directly to the stepper.
    Send the step sequence faster and the stepper should speed up.
    Send it slower and the stepper should slow down.
    You can easily control the speed with a pot, and the direction with a switch.

    If you have a KNOWN working stepper then you can test your driver.
    When you change the pulse rate and direction the stepper should change accordingly.

    When you have a KNOWN working stepper and a KNOWN working driver then you can test your program.

    Either the stepper has a problem, the driver has a problem, the program has a problem, or several or all of them have a problem.

  • It turned out to be none of the above, the problem is with the battery and some of the regulators . I have rectified that problem by using a new battery rated at 14.4 volts at 8000ma, and LM2596S 3A Buck converters. the Bucks cost less than a LM317 and deliver more current.

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