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Slower Motor for Stingray Robot — Parallax Forums

Slower Motor for Stingray Robot

ercoerco Posts: 20,257
edited 2012-10-14 15:32 in Robotics
Just got these lower-geared motors from Ebay China and verified they are an easy bolt-in swap for the stock motors in the Stingray robot. Yes, I'm finally going to build mine! Video shows relative speeds at ~12V. ~$10 each, pretty nice motors.
http://www.ebay.com/itm/170819379020?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 My seller was wholesale-eshop which doesn't list these currently, but there are others out on Ebay, search "DC Gear Motor 12V 70rpm 37mm High Torque 8kg.cm"
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Comments

  • W9GFOW9GFO Posts: 4,010
    edited 2012-10-11 01:11
    The Pololu 350 rpm motors are also rated at 8kg-cm. Considering that you get five times the speed at the same torque I would say that the Pololu motors at $24 are the better deal.

    I think the 150rpm motors (~ 2ft/sec) with 14kg-cm torque would be more appropriate for the Stingray. They are 100% faster and have almost twice as much torque as the Chinese ones, still at $24.

    According to this the stock Stingray motors (HN-35GMB-310rpm) have a pathetic 1.3kg-cm of torque. If that is accurate then even the cheap Chinese motors are an improvement.
  • ercoerco Posts: 20,257
    edited 2012-10-11 06:22
    350 rpm is way too fast. The whole idea for the swap is to slow it down and make it controllable over the full speed range. 100 rpm max speed is more than enough IMO.
  • Martin_HMartin_H Posts: 4,051
    edited 2012-10-11 06:33
    For outdoors line following competitions I would imagine faster is better. But for any sort of dead reckoning navigation control seems better. So I wonder what did the Stingray designers think people would use it for?
  • ercoerco Posts: 20,257
    edited 2012-10-11 06:39
    Martin_H wrote: »
    For outdoors line following competitions I would imagine faster is better. But for any sort of dead reckoning navigation control seems better. So I wonder what did the Stingray designers think people would use it for?

    Good questions. What little I know about reliable navigation says slower is almost always better, so that's my direction, Captain! :)
  • zappmanzappman Posts: 418
    edited 2012-10-11 10:11
    erco wrote: »
    350 rpm is way too fast. The whole idea for the swap is to slow it down and make it controllable over the full speed range. 100 rpm max speed is more than enough IMO.

    I agree 350 RPM is way too fast. I am using a pair of these Pololu 100:1 Metal Gearmotor 37Dx57L mm with 64 CPR Encoder on the robot I have under construction. Key specs of the motors at 12 V: 100 RPM and 300 mA free-run, 220 oz-in (16 kg-cm) and 5 A stall. This 2.71"
  • W9GFOW9GFO Posts: 4,010
    edited 2012-10-11 13:56
    erco wrote: »
    350 rpm is way too fast. The whole idea for the swap is to slow it down and make it controllable over the full speed range. 100 rpm max speed is more than enough IMO.

    I wasn't suggesting that 350 rpm was appropriate for the Stingray. I was pointing out that the 350 rpm Pololu motor is rated at the same torque as the 70 rpm eBay motor. I would prefer the 150 rpm motors as they have loads more torque than the 70 rpm eBay motors AND can drive the robot faster. A robot the size of a Stingray begs to be let out into larger areas. It should at least be able to go as fast as a slow walk.
  • ercoerco Posts: 20,257
    edited 2012-10-11 14:29
    Sure, different strokes (speeds) for different folks. My plans remain low speeds for indoor navigation experiments using this new controller:
    http://embeddedcontroller.weebly.com .

    That Stingray tailwheel looks great, but I suspect a small caster will work better there. I'm just using the parts of the Stingray that suit my evil needs. :)

    I should point out that the original Stingray motors were intended for 7.2V, and all motors discussed here are 12V, so there's a bit of apples & oranges going on. I'm planning on using four 18650 Li-Ion batteries for starters.
  • Matt GillilandMatt Gilliland Posts: 1,406
    edited 2012-10-12 11:26
    Nice find erco!
    -MattG
  • Roger LeeRoger Lee Posts: 339
    edited 2012-10-14 14:53
    Well done erco, well done.

    What do you plan to use for encoders? Or are you making your own out of a band-aid box and toothpicks? ( I know how much you like to roll your own)

    I can't seem to find the specs for the back output shaft. Diameter / length.
  • ercoerco Posts: 20,257
    edited 2012-10-14 15:32
    Yep, I'll make my own wheel encoders, using my obscure and obsolete but oh so onederful (needed another O there) Hamamatsu sensors, P5587 IIRC. This one's gonna be special. Just like the last ten bots. :)
  • ercoerco Posts: 20,257
    $8 each when you buy ten. Team up with four other Stingray owners and save!

    http://www.ebay.com/itm/361086955856
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