Motor Control and Position

Josiah WoodJosiah Wood Posts: 16
edited 2004-09-02 - 11:10:49 in Robotics
What is the best way to control a simple 12VDC motor that I might get from Radio Shack?· I know special considerations must be taken to prevent voltage spikes to the microcontroller, but do I need to buy some type of motor control, or is it easy enough to build a circuit to handle it?

Also, I'm using the motor to control a linear actuator (the motor will turn a threaded screw) which I will need to know the position of.· I don't need it to an extremely high amount of accuracy.· What would be the best way to do this?· I was thinking of·reading the voltage accross a linear potentiometer, but a tachometer might do the job as well.· What would be the most cost-effective solutiton?

Thanks,

Joey

Comments

  • JavalinJavalin Posts: 892
    edited 2004-08-02 - 16:06:02
    Hi,

    Do you need continuous rotation? Ie. ability to rotate 360 degrees+?

    To use a DC motor, you will need a motor controller - and you need to power it seperatly from the stamp/javalin or you will upset the processor! Have a look at http://www.parallax.com/html_pages/products/motorcontrol/motor_control.asp

    If you only need 180 degree's I would recommend using a servo instead, as it solves these issues for you. If you want 360 degree rotation and a position, use a stepper motor & control board - however that seems to be quite expensive. Otherwise use the tachmeter you suggest. Finally if you use a continuos rotation servo you get speed control & 360 degrees - but you'll have to work out a method of counting rotation!

    James
  • Josiah WoodJosiah Wood Posts: 16
    edited 2004-08-02 - 18:20:44
    Yes, I do need 360 degree motion. The motor will turn a threaded screw that will move a nut either forward or backward (to act as a linear actuator), and I need the position of the nut. I don't know if a servo will be fast enough for what I need. The entire robot will be supported by at least 3 of these actuators at any one time, and I would like for them to move fairly quickly. I'm sure I'll lose quite a bit of speed since for every 360 degree rotation of the motor the nut only moves forward one turn.

    Also where can I find tachometers that are compatible with the motor controllers on Parallax? Or a motor with a tachometer built in would be good also if it's cheaper than attaching a tachometer to a $5 motor from RadioShack.

    Thanks,

    Joey
  • JavalinJavalin Posts: 892
    edited 2004-08-02 - 18:48:17
    Hi,

    I guess your in USA, if so have a look at www.hobbyengineering.com - or in the UK try www.activerobots.com / www.techsupplies.co.uk

    You could put a sensor of some type on a fly-wheel attached to the motor? Something on a fly-wheel perhaps, attached to the motor?

    James
  • Josiah WoodJosiah Wood Posts: 16
    edited 2004-08-03 - 14:43:24
    Does anyone have experience with solenoids? Are they easy to control position? I wouldn't be able to use a tachometer with one since it doesn't rotate to control position, but does anyone know where to find cheap linear potentiometers instead (ones that work by a shaft that moves in and out rather than one that is controlled by turning a knob)? All the ones I've found on the internet are very expensive. I don't need great quality, just quantity.

    Thanks everyone for the help,

    Joey
  • BeanBean Posts: 8,119
    edited 2004-08-04 - 15:31:32
    I would look for a slide pot for audio equipment. However most of them will be "audio taper" and you most likely need "linear taper". You should be able to get them fairly cheap.

    Terry
  • Josiah WoodJosiah Wood Posts: 16
    edited 2004-08-04 - 18:55:33
    The terms "slide pot" and "linear taper" should help me get much more specific results than "linear potentiometer". All the search results I've been getting are definitely for more industrial needs and are way overbuilt for my purposes.

    Thanks Terry,

    Joey
  • JohnnyVJohnnyV Posts: 5
    edited 2004-08-12 - 14:51:26
    If you are still looking for a motor controller, I like http://www.hvwtech.com/pages/products_view.asp?ProductID=68 its cheap and ease to build and works great.
  • AntzAntz Posts: 7
    edited 2004-09-02 - 01:43:17
    Have you considered magnetic relays/switches? They are generally bulky so are only practical for physically large projects, but they do act as an effective yet simple proximity switch that can be easily mounted.
    Otherwise, reading the resistance of a a pot that is connected to vary over the range of movement available is probably the simplest way I can think of.

    Post Edited (Antz) : 9/2/2004 1:56:44 AM GMT
  • BeanBean Posts: 8,119
    edited 2004-09-02 - 02:11:03
    Would a stepper motor work for your application ?

    Bean
  • Josiah WoodJosiah Wood Posts: 16
    edited 2004-09-02 - 05:08:47
    Well, I need to know the position to a certain degree of accuracy, so any on/off type of sensor woulnd't be very helpful. And a stepper motor would be too slow, since I need this motor to turn a threaded screw and I want the actuator to move farily quickly. Also, I actually need to control about 26 different motors simultaneously to in turn move 26 different actuators. I've seen servo controllers on Parallax that can control several servos, but I need to control many dc motors. Anyone know of any good resources to do this?

    Thanks everyone,

    Joey
  • BeanBean Posts: 8,119
    edited 2004-09-02 - 11:10:49
    A stepper motor will be much faster than a servo (if you are talking about a hobbie servo like parallax sells).

    Oh wait, I guess that depends on the speed of what is driving the stepper motor...
    I think I remember seeing stepper controller chips that handle the stepping and you just tell it how many steps you want to move.
    I'll see if I can find something on the web.

    Bean
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