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Made Your Own Monster Servo Lately? — Parallax Forums

Made Your Own Monster Servo Lately?

ercoerco Posts: 20,256
edited 2010-02-14 02:03 in Robotics
I have a stockpile of·beautiful Pittman gearmotors, some with lots of gearing and serious torque. What a robot arm I could make out of them. After seeing the prices on the monster servos at https://www.servocity.com/html/spg785a-4_5_servo_gearbox.html·, I'm tempted to build·one myself by gutting a smaller servo for the electronics, adding a same-value potentiometer to my gearmotor and routing the pot & motor leads from the servo to the gearmotor. Just curious if anyone's·tried this·yet and how successful/stable they were.

SPG785_Gearbox_angle.jpg

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·"If you build it, they will come."

Comments

  • WhitWhit Posts: 4,191
    edited 2010-02-11 03:03
    I have not tried this or seen it. It sure looks cool though!

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    Whit+


    "We keep moving forward, opening new doors, and doing new things, because we're curious and curiosity keeps leading us down new paths." - Walt Disney
  • ercoerco Posts: 20,256
    edited 2010-02-11 03:44
    My EE pals at work like my concept, but they warn that the current & voltage demands of a much larger motor will overwhelm the servo's original electronics. Fine, I can make a beefier H-bridge out of 4 power transistors or FETs and drive that with the servo's motor wires.

    Assuming that works, I can make a motor driver out of any continous rotation (or any, really) servo plus 4 transistors. Servos range in price, but there are some cheapies out there. In a thread a while back, someone provided a link to a site that sold micro servos for under $3. That's worth ordering a dozen servos and some experimental gutting.

    Now if I can just find that site!

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    ·"If you build it, they will come."
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2010-02-11 04:21
    erco, if the search worked, I would point you to a cordless screwdriver mod I posted a few years ago...

    Edit:
    here is the link...
    http://forums.parallax.com/showthread.php?p=525689

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.

    Post Edited (Beau Schwabe (Parallax)) : 2/11/2010 4:27:39 AM GMT
  • Roy ElthamRoy Eltham Posts: 3,000
    edited 2010-02-11 04:51
    erco,

    Here's that link to the under $3 micro servo: http://www.hobbypartz.com/topromisesg9.html
    They have a lot of cheap servos of all sizes. Several under $10 and under $5.

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    Check out the Propeller Wiki·and contribute if you can.
  • ercoerco Posts: 20,256
    edited 2010-02-11 05:32
    @Roy: Thanks, that's exactly the servo I remembered. You're on it, Pal!

    @Beau : DOH, Beau! As ever, you're several steps and years ahead of me. I'll check with you before posting my next "bright idea" and you can point me towards your fine body of pre-existing work. Ah well, at least my powers of reasoning pointed me in the right direction. Thanks for the cross-check and schematics, I do want to make some of these and get my 40 Pittman motors under control.

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    ·"If you build it, they will come."
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2010-02-11 08:57
    erco,

    thanks! ... in my cordless screwdriver mod, I mentioned fixing the original servo pot. You could just as easily mechanically link a pot (geared up/down, or the same) to the screwdriver and have a really big, very high torque servo.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • Tom CTom C Posts: 461
    edited 2010-02-11 17:21
    erco,

    I have made several monster servos using the VEX Robotics dc motors, a 5k/10k feedback pot, and the Lynxmotion servo driver board that can handle around 2 amps continuous. I have the VEX Robotics dc motors geared down by 40 to 1 and am using them to power the joints on my robotic arm. Works great.

    Regards,

    TCIII

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    If you are going to send·a Robot·to save the world, you·better make sure it likes it the way it is!
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-02-12 04:24
    To control large motors you could always use a relay. I was able to get 2 of them @ 44 cents each today at radioshack and they are rated for 5 amps. One of them is able to control motor direction and paired with a transistor can regulate speed.

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    PG
  • ercoerco Posts: 20,256
    edited 2010-02-12 17:17
    @Pi Guy: Thanks, I love relays and use them all the time. I'm trying to break out of that habit. Making a servo-like action using relays requires at least 3 IO pins (2 motor plus 1 feedback pot) and constant monitoring. A real servo uses just one (add a servopal and there's no more constant monitoring), so I'm interested in making make giant servos out of affordable little ones.
    PS: TWO relays for 44 cents? Sign me up, you're winning me back over to the dark (relay) side! Which ones?

    @Tom: Also thanks for your input. I'm sure that Lynxmotion board can do it all. I just love re-inventing the wheel and trying to come up with cheap, clever workarounds.

    And I would have gotten away with it, too, it it wouldn't have been for that dang Beau Schwabe!
    He's already done ALL the good stuff! [noparse]:)[/noparse]

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    ·"If you build it, they will come."
  • Beau SchwabeBeau Schwabe Posts: 6,566
    edited 2010-02-13 23:24
    erco ... LOL! "...brush on ... brush off..." smilewinkgrin.gif

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • P!-RoP!-Ro Posts: 1,189
    edited 2010-02-14 02:03
    It was 44 cents each, a little over a dollar for two with tax. That was at 50% off, though [noparse];)[/noparse] Turns out its good to befriend RS employees, seems to turn out for the best sometimes. Especially since I had to go there again today due to shorted parts--and I got the same deal from someone else!

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    PG
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