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Re: [SeattleRobotics] Sources for worm drive parts

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  • Tom Capon
    Windshield wiper motors have worm gears. but they are pretty big, and generally go for, yes, $20 where I ve been able to find them. You might be able to get
    Message 1 of 6 , Apr 2, 2005
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      Windshield wiper motors have worm gears. but they are pretty big, and
      generally go for, yes, $20 where I've been able to find them. You
      might be able to get some burnt-out ones at a garage (or several
      garages), with good gears in them still.
    • douglas_warren_bell
      Power window motors, both in doors and some station wagon tailgates, and power seat motors also use worm gear drives. They have an advantage that they re
      Message 2 of 6 , Apr 18, 2005
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        Power window motors, both in doors and some station wagon tailgates,
        and power seat motors also use worm gear drives. They have an
        advantage that they're designed to be powered in both directions, as
        opposed to the windshield wiper motors which may work well in only one
        direction, for example because the thrust bearing on the worm gear may
        work only in one direction. Also, you can get four or five per car,
        vs. one windshield wiper motor and sometimes one back window wiper
        motor. On the other hand, a windshield wiper motor is designed to
        operate continuously, as opposed to an electric window motor which is
        probably designed to operate intermittantly, so it might overheat in
        continuous use. I've also heard that these automotive motors are not
        very efficient, probably because plenty of power is available in a car
        compared to in a small mobile robot.

        A good source for automotive motors is junk yards - some places allow
        you to go out into their yard with your own tools and pull the motors
        yourself. There's a "You Pull" place on Aurora somewhere north of
        Seattle.

        When I was in high school, my dad and I went out to one of these
        places and pulled the door window motors, the power seat motors and
        the tailgate window motor out of a car. We also got the scissor units
        that move the windows. The power seat motors came with flexible
        shafts, and the gear reductions were separate units, also worm drive
        as I recall. I'm sure we paid way less than $20 per motor, but I don't
        know how much they would charge now, though I'm sure it would be way
        less than if you bought them at Shucks, etc.

        Two power window motors and a car battery powered a robot that moved
        at a pretty good clip, using lawnmower wheels engaged directly to the
        window motor output shafts.

        Some of these motors are specially wired - they have a two pin
        connector, but you don't apply power across the two pins. Instead, you
        apply power between one pin and the chassis to drive the motor one
        direction, or between the other pin and the chassis to drive the motor
        the other direction. I believe this is accomplished by having a center
        tapped field coil winding, with the center tap connected to one brush
        and the other brush connected to the chassis. The two pins in the
        connector are connected to the two sides of the field coil. This
        simplifies the switching required to control these motors in a car.

        Instead of using an H-bridge on such a motor, you only need a couple
        of PNP transistors. Or, you should be able to connect the chassis to
        the + side of your battery and use a pair of NPN transistors, or N-
        channel power MOSFETs, although you couldn't do dynamic braking with
        this connection, but dynamic braking is less important when using worm
        gear reduction.

        Actually, in order to do dynamic braking, you'd have to power the
        field coil and short out the armature, so you'd have to open the motor
        and add a connection to the other side of the armature.

        If you used an H-bridge with such a motor, connected it to the two
        field connections, and connected the chassis to the + supply, the low
        side drivers would do most of the work; the high side drivers would
        increase the current across the field coil, and reduce the current
        through the armature. To turn the motor off, you'd have to be able to
        command the H-bridge to pull both sides up. Or, if you connected the
        motor chassis to the - side of the battery, the high side drivers
        would do most of the work, and you'd have to command the H-bridge to
        pull boths sides down to turn the motor off. This might work better or
        worse than connecting the H-bridge to one field coil pin and the
        chassis.

        The power window motors in the FIRST kits were not wired this way. The
        technique may not be used anymore, perhaps because new more powerful
        magnets may make it more cost effective to use permanent magnet fields
        even though it takes twice as many contacts on the switches to reverse
        them.

        Doug Bell

        --- In SeattleRobotics@yahoogroups.com, Tom Capon <robot256@g...>
        wrote:
        > Windshield wiper motors have worm gears. but they are pretty big,
        and
        > generally go for, yes, $20 where I've been able to find them. You
        > might be able to get some burnt-out ones at a garage (or several
        > garages), with good gears in them still.
      • Robert Hedan
        Just a suggestion for those dismayed at the weight of an automobile battery. Check out the batteries for motorcycles at places like Canadian Tire. I don t
        Message 3 of 6 , Apr 18, 2005
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          Just a suggestion for those dismayed at the weight of an automobile battery.
          Check out the batteries for motorcycles at places like Canadian Tire. I
          don't know the equiovalence in the States, but it's a store that originally
          started as a bicycle repair shop, and has grown to include just about
          anything for the garden, tools, sports, bicycles, car parts/repair/fuel, to
          small home appliances and workshop doodads.

          Large motorcycles also operate on 12volts DC, but with a more compact sealed
          battery than the ones in cars. The smaller bikes have 6 volts and are even
          smaller, about the size of those battery packs for cordless tools. The
          clerk at these stores know their stuff and can recommend to you a cheap
          aftermarket model with sufficient amperage for your project. Yashua is a
          popular brand here in Quebec, they make batteries for most if not all bikes.

          Robert
          :)


          -----Message d'origine-----
          De : SeattleRobotics@yahoogroups.com
          [mailto:SeattleRobotics@yahoogroups.com] De la part de douglas_warren_bell
          Envoyé : avril 18 2005 09:10
          À : SeattleRobotics@yahoogroups.com
          Objet : [SeattleRobotics] Re: Sources for worm drive parts - power window
          motors




          Power window motors, both in doors and some station wagon tailgates,
          and power seat motors also use worm gear drives. They have an
          advantage that they're designed to be powered in both directions, as
          opposed to the windshield wiper motors which may work well in only one
          direction, for example because the thrust bearing on the worm gear may
          work only in one direction. Also, you can get four or five per car,
          vs. one windshield wiper motor and sometimes one back window wiper
          motor. On the other hand, a windshield wiper motor is designed to
          operate continuously, as opposed to an electric window motor which is
          probably designed to operate intermittantly, so it might overheat in
          continuous use. I've also heard that these automotive motors are not
          very efficient, probably because plenty of power is available in a car
          compared to in a small mobile robot.

          A good source for automotive motors is junk yards - some places allow
          you to go out into their yard with your own tools and pull the motors
          yourself. There's a "You Pull" place on Aurora somewhere north of
          Seattle.

          When I was in high school, my dad and I went out to one of these
          places and pulled the door window motors, the power seat motors and
          the tailgate window motor out of a car. We also got the scissor units
          that move the windows. The power seat motors came with flexible
          shafts, and the gear reductions were separate units, also worm drive
          as I recall. I'm sure we paid way less than $20 per motor, but I don't
          know how much they would charge now, though I'm sure it would be way
          less than if you bought them at Shucks, etc.

          Two power window motors and a car battery powered a robot that moved
          at a pretty good clip, using lawnmower wheels engaged directly to the
          window motor output shafts.

          Some of these motors are specially wired - they have a two pin
          connector, but you don't apply power across the two pins. Instead, you
          apply power between one pin and the chassis to drive the motor one
          direction, or between the other pin and the chassis to drive the motor
          the other direction. I believe this is accomplished by having a center
          tapped field coil winding, with the center tap connected to one brush
          and the other brush connected to the chassis. The two pins in the
          connector are connected to the two sides of the field coil. This
          simplifies the switching required to control these motors in a car.

          Instead of using an H-bridge on such a motor, you only need a couple
          of PNP transistors. Or, you should be able to connect the chassis to
          the + side of your battery and use a pair of NPN transistors, or N- channel
          power MOSFETs, although you couldn't do dynamic braking with
          this connection, but dynamic braking is less important when using worm
          gear reduction.

          Actually, in order to do dynamic braking, you'd have to power the
          field coil and short out the armature, so you'd have to open the motor
          and add a connection to the other side of the armature.

          If you used an H-bridge with such a motor, connected it to the two
          field connections, and connected the chassis to the + supply, the low
          side drivers would do most of the work; the high side drivers would
          increase the current across the field coil, and reduce the current
          through the armature. To turn the motor off, you'd have to be able to
          command the H-bridge to pull both sides up. Or, if you connected the
          motor chassis to the - side of the battery, the high side drivers
          would do most of the work, and you'd have to command the H-bridge to
          pull boths sides down to turn the motor off. This might work better or
          worse than connecting the H-bridge to one field coil pin and the
          chassis.

          The power window motors in the FIRST kits were not wired this way. The
          technique may not be used anymore, perhaps because new more powerful
          magnets may make it more cost effective to use permanent magnet fields
          even though it takes twice as many contacts on the switches to reverse
          them.

          Doug Bell

          --- In SeattleRobotics@yahoogroups.com, Tom Capon <robot256@g...>
          wrote:
          > Windshield wiper motors have worm gears. but they are pretty big,
          and
          > generally go for, yes, $20 where I've been able to find them. You
          > might be able to get some burnt-out ones at a garage (or several
          > garages), with good gears in them still.





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        • Rich Chandler
          ... On important thing to note. If you DON T have this double-tap system, and instead have to reverse the current through a chassis-ground motor to get
          Message 4 of 6 , Apr 18, 2005
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            At 1:09 PM +0000 4/18/05, douglas_warren_bell wrote:
            >Some of these motors are specially wired - they have a two pin
            >connector, but you don't apply power across the two pins. Instead, you
            >apply power between one pin and the chassis to drive the motor one
            >direction, or between the other pin and the chassis to drive the motor
            >the other direction. I believe this is accomplished by having a center
            >tapped field coil winding, with the center tap connected to one brush
            >and the other brush connected to the chassis. The two pins in the
            >connector are connected to the two sides of the field coil. This
            >simplifies the switching required to control these motors in a car.
            >
            >Instead of using an H-bridge on such a motor, you only need a couple
            >of PNP transistors.

            On important thing to note. If you DON'T have this double-tap
            system, and instead have to reverse the current through a
            chassis-ground motor to get differential steering, you can set up a
            condition where you've shorted out your speed controller/h-bridge
            when one side is driving forward than the other in reverse, since one
            side will be connecting + to the chassis and the other will connect -
            through the chassis. This is not as much of a problem if you use a
            non-metallic frame, but some motors turn out to be conductive through
            the shaft and therefore your drive train.

            Always check for continuity through the motor shaft. Sometimes a
            motor that seems to work well only burned up a little, enough for the
            windings to contact the armature in one spot.
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