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What motor controller should our team get to control 20 motors? — Parallax Forums

What motor controller should our team get to control 20 motors?

leiji81leiji81 Posts: 7
edited 2006-01-31 17:00 in Robotics
Hi everyone,

We are building a biomedical device that requires vibration for a senior design project. We have decided to use small cheap pager motors in order to achieve this.

We are using the BASIC Stamp Discovery Kit with the BOE and BS2.

Yesterday, we tried to·control a motor through HIGH and LOW, and burned our chip so we have to order another one.

Basically all of these motors will be connected parallel (they do not need to be independently controlled, we just need them to vibrate).

Could one of you with experience please recommend a motor controller that we can easily use with the BOE and BS2 stamp to control these motors?

Thanks in advance!

-leiji81

Comments

  • leiji81leiji81 Posts: 7
    edited 2006-01-31 06:32
    These are DC motors that worked when we plugged them directly into the BOE board's Vdd and Vss
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-01-31 13:33
    Ok you dont need anything as fancy as a motor cotroller, afterall your not going to be able to discern the difference between it vibrating from rotating in one direction as opposed to the other direction. A simple FET or BJT would work. Also most pager vibrators are designed to operate off of 3V, so you probably shouldn't be operating them at 5V for more than a brief period if you want them to last for a while (this means you should put a resitor in line to drop the voltage seen by the motors to 3V). In general if you dont know how much current a device needs you shouldn't directly connect them to a stamp (a stamp pin can only handle a 20mA load before you risk permanently damaging the pin). Jon has posted the schematic for both FET and BJT drivers many times, but I can't search for them at the moment (my computer has a quirky habit of becoming blind to the DNS after being left unattended for a few hours, and I havn't rebooted this morning yet, so all I can access are the forums till reboot), but you can try yourself at http://search.parallax.com terms like: Jon Williams FET, may work.

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  • leiji81leiji81 Posts: 7
    edited 2006-01-31 16:35
    Sorry, forgot to mention earlier. We will need to control the frequency of vibration of these pager motors. From your reply it seems like we will actually need a controller?

    Thanks!

    leiji81
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-01-31 16:44
    Ok using the keywords I provided, the second post of the third link ( http://forums.parallax.com/showthread.php?p=521472) had this schematic (posted by Jon Williams):

    attachment.php?attachmentid=36816


    Since you dont want individual control of the motors, you would just connect the motors in parallel. A resistor should be placed in series with all the motors, to calculate the value of the resistor, measure the ohms of a single motor with a DMM, then plug into this equation R= Rmotor/30, pick the next highest value for a resistor availible. (A brief explaination for the equation, for 20 motors in parallel each having a resistance of Rmotor, the total resistance of all of them in parallel is Rmotor/20. We want the voltage drop across them to be 3V so the current flowing through the total motor assembly is I=V/Rmotor(total)=3/(Rmotor/20)=60/Rmotor (Ohm's Law). If the voltage supplied to the motor assembly is 5V, then we want a 2V drop across the resistor, again using Ohms law Rres=Vres/I=2/(60/Rmotor)=Rmotor/30. )


    Also make sure the voltage regulator can supply the amount of current required (60/Rmotor), if not, you'll have to supply a seperate supply for the motors (connect the grounds of the two supplies together).

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  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-01-31 16:51
    Ahh, PWM control, If you stamp doesnt have to do anything else while its activating the pagers, you can try to drive the above circuit with the PWM command (While the PWM command was designed for production of analog voltages, you may find it suitable for motor control), if you do have to do other things then you will indeed need an external controller.

    If you go the controller route, look into:

    http://www.parallax.com/detail.asp?product_id=30001

    http://www.parallax.com/detail.asp?product_id=30002

    http://www.parallax.com/detail.asp?product_id=27961

    and http://www.parallax.com/detail.asp?product_id=30052

    read the specs of each to make sure they are suitible for you application (current draw, PWM control etc).

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    Post Edited (Paul Baker) : 1/31/2006 4:55:07 PM GMT
  • leiji81leiji81 Posts: 7
    edited 2006-01-31 17:00
    Thank you so much Paul!
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