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How fast is the string ray robot? — Parallax Forums

How fast is the string ray robot?

KyeKye Posts: 2,200
edited 2009-12-26 17:09 in Robotics
I plan on buying one for the Mobot Competition at Carnegie Mellon University, but I'm not sure if its fast enough to beat some records.

My measurement would be how long does it take to travel a meter.

Thanks,

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Nyamekye,

Comments

  • Sal AmmoniacSal Ammoniac Posts: 213
    edited 2009-12-03 00:24
    A review I read in Nuts & Volts said 6 feet/sec.
  • allanlane5allanlane5 Posts: 3,815
    edited 2009-12-03 14:25
    So, that would be 2 meters per second.
  • SailerManSailerMan Posts: 337
    edited 2009-12-03 19:33
    Actually 1.8288 meters/Sec [noparse]:)[/noparse]
  • NakNak Posts: 36
    edited 2009-12-09 20:04
    If this is insufficient, you can always configure your Stingray with larger motors and a bigger battery. One of the great things about this kit is there's plenty of room for expansion! It's quite solidly constructed, too, so should be relatively robust against "un-programmed sudden deceleration" events...
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-12-09 20:35
    Hello everyone,

    The rated output of the shaft on the gearbox at the rated voltage is 310 RPM. To calculate speed in inches/second you would use the formula Speed = (RPM (diameter * PI) / 60). So given 310 RPM and the wheel diameter of 4-7/8" this comes out to 2 meters/second or 6.57 feet/second.

    Nak is correct though, the chassis was designed with modding in mind. The gauge of the metal is low enough to make it easy to mill while maintaining stability. We settled on the gearbox motors we have because of the price/performance ratio. Inevitably there are some (including myself) who would spend more money for higher performance. We originally tested some 12V motors that had built-in encoders. I don't remember where we got them from, but I will attach a picture of these motors next to the current motor (pulled from my Stingray) for comparison.

    Note that these motors had a larger output shaft and were rated at 12V, but they also had built-in quadrature encoders (something we'll have real soon). Variance in speed between these motors at the same voltage was pretty significant too, which is probably why they have the encoders built-in. But the main thing is these were quite expensive.

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    Chris Savage

    Parallax Engineering
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    1152 x 864 - 140K
    1152 x 864 - 103K
  • John AbshierJohn Abshier Posts: 1,116
    edited 2009-12-09 20:47
    The 310 rpm is probably under no load. Maximum power output is usually at about 1/2 no load speed. So max speed will depend on how heavy your Stingray is, ground conditions (hard floor or shag carpet), and going uphill or downhill. Also if you are running at 100 percent power, you cannot speed up a motor to turn. Of course you can slow down the other motor. I usually add to one motor and subtract from the other.

    John Abshier
  • NakNak Posts: 36
    edited 2009-12-09 22:43
    If anyone sources the motors Chris pictured please post info here... I was planning to look for something exactly along these lines. smile.gif
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2009-12-09 22:53
    Actually, in retrospect, I think we got them from the manufacturer printed on the label. I believe they runs ads periodically in Nuts & Volts and/or Servo and/or Robot magazine. That's how I found them the first time.· In fact, here's the link: http://www.shayye.com.tw/EngVer/Products-micro/microList.htm

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    Chris Savage

    Parallax Engineering
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    ·
  • Ray0665Ray0665 Posts: 231
    edited 2009-12-26 17:09
    I'm very Interested in the wheel encoders for the stingray you mentioned above where can I get them?
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