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9G Continuous Rotation Servo — Parallax Forums

9G Continuous Rotation Servo

ercoerco Posts: 20,257
edited 2015-09-28 00:23 in Robotics
Just saw this $5 9g CR servo: https://www.pololu.com/product/2820 A pair of IMO too-big wheels also costs $5: https://www.pololu.com/product/2819

Parallax, you should sell these servos too. I have modified a lot of HXT900s for CR because I didn't think anyone had any at a reasonable price. They are great for small tabletop robots. Duane or anyone, do you know of any others for sale?

Edit: I see Robotshop (UGH!) also sells them: http://www.robotshop.com/en/9g-continuous-rotation-micro-servo.html

(Also see this cheap TOF distance sensor : https://www.pololu.com/product/2489 0-10cm w/mm accuracy Use coupon code VL6180X through September 30 to get one of these modules for just $6.95 (42% off)!)

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2015-09-28 03:59
    Adafruit sells some. I think these are relatively new. They're not listed under their "robotics" stuff for some reason.

    https://adafruit.com/products/2442

    Lumi, one of my friends over at Let's Make Robots, passed away a few months ago. He made a fun little desktop robot.

    http://letsmakerobots.com/node/38560
    My conversation with Lumi about his robot has now been deleted by the new dictators owners. (I never requested they delete any of my posts.) I wish I had thought to save our conversation.
    Sorry for the somber note.
    I think it's great these little continuous rotation servos are available ready made. I understand these little servos aren't as simple to convert as the normal size servos.
  • Martin_HMartin_H Posts: 4,051
    @Duane, your friend's little bot is neat.
  • ercoerco Posts: 20,257
    Agreed, really neat little bot and I'm sorry to hear about your friend. Very talented, from his short writeup.
  • GordonMcCombGordonMcComb Posts: 3,366
    I worry about reliability. The gears on these things strip just by looking at 'em crosswise.

    Then again, for five bucks...
  • ercoerco Posts: 20,257
    edited 2015-09-28 19:26
    Hey, the master is back! I was a day away from emailing you to see where you have been.

    TTYTT, the gears in these 9g servos are downright beefy compared to the cheap little steppers on Ebay. But yes, still relatively delicate, that's why I said those wheels are too big in my OP. Lightweight bots with little wheels, like the one Duane shared, would be best for these 9-grammers.
  • GordonMcCombGordonMcComb Posts: 3,366
    I've been around, but have been busy with some other bidness.

    I'm guessing the wheel is the only one Feetech is offering with the smaller spline to match the servo. Pololu typically puts small wheels on small bots, and they're well aware of the technical ramifications of using larger diameter wheels. But the small wheels they sell are engineered with hubs unique to the tiny motors they sell.

  • ercoerco Posts: 20,257
    I ordered some servos & wheels, will advise & Youtube.
  • ercoerco Posts: 20,257
    edited 2015-10-02 21:56
    Got 'em, the wheel are nice, but the servos are pretty bad quality. I tested two and they both have poor low RPM control, and uneven RPM from binding. They're going back.

    What a shame. The HXT900 servos I modded are vastly superior, with fine motor control and nice even RPM.



  • GordonMcCombGordonMcComb Posts: 3,366
    Well that settles it, then. Forthwith, we will be ordering all our micro servos from Erco Enterprises Inc. I assume like Larry over at Sit & Sleep, you'll match anyone's advertised price for CR micro servos, or your motor is FREEEEEE!

    PS: You didn't have any other plans for your kitchen table, did you, like eating on it? You can inform Mrs. Erco the table is now a workbench.
  • ercoerco Posts: 20,257
    Shhhhhhhhhh, all true but I have to break the news to her slowly, after our anniversary...
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    I got some of these a couple days ago and have just started testing. Ugh! Not only does the one I tested show erratic speeds, but with the same pulse widths it can start out fast, then slow down.

    At first I was willing to give it the benefit of the doubt, since I was testing without a load near the newly-widened dead zone. But I'm convinced now that that has nothing to do with the poor performance.

    Mine are going back, too. Bummer.

    -Phil
  • ercoerco Posts: 20,257
    Phil Pilgrim (PhiPi) wrote: »
    Mine are going back, too. Bummer.

    I swapped a few emails with ben@pololu.com and got him to give me an RMA waiving their return and restocking fees. Those are pretty bogus fees since I'm already paying postage both ways.

  • ercoerco Posts: 20,257
    edited 2015-10-12 01:48


  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    I sent mine back with the promise of a full refund, except for the shipping charge. I'm guessing that the performance issue has something to do with the gears. I noticed that one was tilted off axis a bit as I viewed it through the transparent case.

    I'm sure there are apps where they would be suitable, as long as smooth low-speed rotation was not one of the requirements.

    -Phil
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