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Cheap Motors — Parallax Forums

Cheap Motors

WhitWhit Posts: 4,191
edited 2015-02-17 19:26 in Robotics
Saw these in an ad tonight - might make for a fun cheapie bot - http://www.mpja.com/02-17-15.asp?r=265527&s=35

Ad says "Reversible small DC motor with a 2.5in. Dia. X 1in. wide rubber tire. Rated: ~130RPM @ 3V/.15A No Load; ~275RPM @ 6V/.2A No Load. Plastic multi stage reduction right angle gear head. Solder terminals. For toys, RC trucks & cars, robots etc.
L: 3-3/8in. W: 2-5/8in. H: 2-1/2” WT: .14"

Pretty high RPM though...

attachment.php?attachmentid=113209&d=1424142822
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280 x 210 - 18K

Comments

  • tonyp12tonyp12 Posts: 1,950
    edited 2015-02-16 19:20
    $7 for the pair here: (wheels are on backorder)
    https://www.sparkfun.com/products/13258
    https://www.sparkfun.com/products/13259
  • WhitWhit Posts: 4,191
    edited 2015-02-16 19:36
    Way better gear ratio too tonyp12! At least it looks so...
  • Duane DegnDuane Degn Posts: 10,588
    edited 2015-02-16 19:51
    Just don't get the "Dual Motor Drive for Toy" from MPJA.

    18310.jpg

    The motors don't have any gearbox which makes them useless for driving the wheels. I've wondered many times how this set could be designed and manufactured without anyone bothering to test them.

    I've attempted to write a review on the MPJA website but my review never showed up.
  • WhitWhit Posts: 4,191
    edited 2015-02-16 19:57
    Duane Degn wrote: »
    I've attempted to write a review on the MPJA website but my review never showed up.

    LOL! I bet. ;-)

    Wonder if they always 'moderate' unfavorable reviews?
  • ercoerco Posts: 20,255
    edited 2015-02-16 20:51
    Save your money, Br'er Whit. Those look nice, but they are the same junky 1:48 gearboxes that come with the Magician chassis. Too fast, not enough gear reduction. No torque, no power, hard to find two going the same RPM to make a bot drive straight. I've tried, Gordon's tried. An exercise in frustration and futility.

    Phew, I started to panic looking at the MJPA site. They don't stock my favorite gearmotors anymore, but fortunately All Electronics still does. My highest recommendation, IMO every roboticist needs at least 4 of these on hand at all times for that next medium size robot build. http://www.allelectronics.com/make-a-store/item/dcm-351/24-vdc-gear-motor-w/turntable/1.html

    They are high voltage (24VDC) and low current. Perfect candidates for being controlled by a cheap L298N h-bridge: http://www.ebay.com/itm/Dual-H-Bridge-DC-Stepper-Motor-Drive-Controller-Board-Module-Arduino-L298N-DX-/251654649555
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2015-02-17 13:58
    If you don't need your robot to go in a straight line these motors are okay. They're fine in applications where there's some form of feedback loop to compensate for the mis-steering from low torque of the motors. An example might be a line follower.

    My fav is a cheapo 3-speed Tamiya gear motor, which you can build in any of three ratios. Couple it with a matching Tamiya tire, of which there are several varieties to choose from. Then, replace the 3V motor with one of these:

    https://www.pololu.com/product/1117/

    Now you have a motor that can be easily driven with an H-bridge, and consumes far less current even at stall. An L298 works quite well with this motor.

    More than $4 for a wheel/tire set (more like $10 or so), but worth it.
  • WhitWhit Posts: 4,191
    edited 2015-02-17 19:26
    Thanks everyone! That is why I posted - I knew I would get great feedback! Thanks for keeping a guy out of a bind - even if it was a cheap bind!

    @ erco - digging the twin bot design avatar!
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