vibrating stepper motors!

Discussion in 'The Projects Forum' started by kutalinelucas, Jun 30, 2011.

  1. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
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    0
    Hey guys,

    I'm looking for a little help. I'm just trying to do the old stepper motor (hybrid-bipolar) using a basic stamp 2 chip with a L293D push-pull driver.

    All looks good when I attach LEDs to the output of the driver, where switching brings the voltage between 4 - 8v. When I hook the stepper up to the ports there is only a voltage of ~0.3 on the output pins and the stepper vibrates quite slowly. The shaft also turns very easily by hand

    I have 9v Powering the driver and 5v VDD from a DC adapter so I don't think power is an issue

    I think the step sequence is ok, and I'm pretty sure its wired up correctly but I'm just short of banging my head against the wall. I've been playing about for a fair few hours so any suggestions would be greatly appriciated.

    Cheers

    Martyn
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    All stepping motors are not created equal.
    Can you give us the colours of the wires on the motor?
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    You also mention that you are driving the motor(s) with 9v - is that a PP3 "transistor" 9v battery, by chance? If so, those have very little power in them.

    It would help a great deal if you posted the stepper motors' manufacturer name and part number; we could then track down a datasheet.
     
  4. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
    98
    0
    Hey, thanks for the replies.

    I'm using 9v from a DC -plug-in-the-wall converter, the stepper motor is a nema 8 (20mm) FL20STH33-0604B which I am (trying) to drive with a L293D push-pull driver. The vdd (of the h-bridge ic) is +5v where the Vin is held at 9v. With the LED's attacted to the outputs, It supplies a logic of between 3 -8v on the output pins, but barely nothing when the stepper is attached.

    With the wire colours, there is green, red, black and blue. By measuring the res across each wire, I've paired them which is the same on the data sheet and attached green & black to outputs 1&2; and red & blue to the other.

    Its all on a breadboard at the moment but I could draw a ciruit diagram, or help with any other information...

    Thanks for the help...

    Martyn
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Just for convenience, the datasheet for the motor is on the 2nd page of this PDF:
    http://www.motioncontrolproducts.com/pdfs/fl20-28.pdf

    Looking at a datasheet for the L293D: http://www.st.com/stonline/books/pdf/docs/1330.pdf
    I see that 600mA is the max for this driver.

    On page 3, for Vce(sat)H, sourcing 0.6A, the drop is typically ~1.4v, but can be up to 1.8v.
    For Vce(sat)L, sinking 0.6A, the drop is ~1.2v to 1.8v.
    So, you could have 9v-(1.4v+1.2v) = 6.4v to 9v- (1.8v+1.8v) = 5.4v across the stepper motors' windings, IF the supply is staying at 9v when the load is applied.

    It could be that your breadboard is old and the connections are corroded/weak.
    Are you certain that you are using the proper gauge wire for the breadboard?
     
    Last edited: Jun 30, 2011
  6. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
    98
    0
    Hey, I must be honest but my circuit theory isn't up to much !

    With the LED running i measured 35 uA coming out of the driver (with the mutlimeter set to 2000uA(?)) and 180uA (still set to 2000uA) on the supply rail.

    I have a voltage regulator to drop the 9v supply down to 6v for the vdd...is there any way i've created a current divider or something? as I said I could probably knock up some sort of diagram if it would help you help me get on my way

    With regards to the wire, it's solid core standard prototyping wire (0.8mm i think). The wires to the stepper was supplied with the motor. Its fairly thin but as it was supplied i'm guessing its ok

    With regards to the breadboard, i think its ok. I've been proding at it with a multimeter all day and haven't really noticed any loose connections or servere voltage drops...
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,009
    1,530
    The rated voltage (name plate voltage) of a stepper motor is not the voltage that they should be ran at. The motor supply voltage should be between 10 and 20 times the name plate voltage.

    Also if you are trying to start the motor at a fast speed from a dead stop they will do what you describe in your first post, just sit there and vibrate. They must be 'ramped up' to a fast RPM from a dead stop. This is especially true if the voltage is not high enough or the amperage is not correct.
     
  8. kutalinelucas

    Thread Starter Active Member

    Nov 20, 2007
    98
    0
    well i think the rated voltage is 4.6v (ish). Its only a 20mm stepper, so you think it should be run at 40-80v? as I said my circuit theory isn't up to much but that seems pretty excessive.

    About the speed ramp-up, I'll give that a try, I was just following a parallax tutorial initially and I know how badly those sort of tutorials can be...

    From tutorials I have looked up on the web, the general consensus is that 5v should be used to power the driver, and 12v at the Vin of the driver to run the motor.

    I did (acidentally) get the stepper to run as it should earlier on today, this is why i'm thinking it may be a current issue, but then when I replace the LEDs with the motor, the voltage on the output pins drops from 8v to 0.5v, and I don't know why, or where this voltage is going. Could it just be that it is magnetising the magnets? I really don't know.

    I may have to play about with the voltage regulator, or possibly try driving the ic's with 4 AA batteries and the Vin with the 12v available with the DC adapter...see if I can get a tidy response.

    I will try everything above, but if to no avail, is there any thing else Which may be worth a try?
     
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