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$16 Metal Robot Chassis — Parallax Forums

$16 Metal Robot Chassis

ercoerco Posts: 20,257
edited 2016-06-11 16:01 in Robotics
Good looking red anodized chassis. Uses DC motors, gutted 9g servos, so you'll need an h bridge or relays to drive. Light duty, not as strong as Boebot's full sized servos & wheels. http://www.ebay.com/itm/2WD-Two-Wheel-Drive-Metal-Smart-Robot-Car-Chassis-Arduino-DC-Motor-DIY-USA-/262454223855. Chassis appears to have 3 more servo cutouts for 4WD and an ultrasonic servo. I nabbed one.

Sold by another new California robotic startup with lofty goals: http://www.barnabasrobotics.com

s-l1600.jpg

Comments

  • GordonMcCombGordonMcComb Posts: 3,366
    Looks pretty good.

    I think that's powder coated and not anodized -- only Parallax would spend the extra dollars for anodizing, which is generally the better surface treatment.

    Nice to see another startup in this space. Shows the growth potential. And, still leaves open our new company, Barabbas Robotics.
  • ercoerco Posts: 20,257
    Give us Barrabus (robotics)!
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    erco wrote:
    Chassis appears to have 3 more servo cutouts for 4WD and an ultrasonic servo.
    ... or a steerable idler wheel.

    -Phil
  • ercoerco Posts: 20,257
    edited 2016-06-12 14:29
    AKA rudder per Tommy Tailspin! The more I think about his system, the more I like it. A steered rubber wheel actively improves tracking in straight travel and curves. Coordinated with differential steering, it might just yield a usable dead reckoning system with perhaps just one wheel encoder to measure distance & turns. Whether to put said encoder on the driven wheel or steered idler wheel for best consistency is TBD.

    This chassis might also balance upright, using no casters at all.
  • ercoerco Posts: 20,257
    Chassis arrived and is very nice. Per Gordon's comment, I was expecting powder coating but it is in fact red anodized and looks great. Turns out it's a kit by Feetech (formerly FiTec), model FT-MC-001. Mysteriously, it doesn't appear on Feetch.com, but Googling it, it shows up several places. On Aliexpress for $16.83: http://www.aliexpress.com/item/10-pcs-wheel-for-9g-360-Degree-Continuous-Rotation-Micro-Robot-Servo-FS90R/32607362464.html

    Has the nice wheels I recommended elsewhere, and a solid, heavy, ball bearing caster which seems way overdone on this little bot.

    Not sure how this California seller is making any money selling it for $15.99, it cost him $2.50 just to mail it to me. Edward sounds like an interesting fellow. I contacted him, we're meeting up soon.
    20160616_120948.jpg
    1764 x 1422 - 453K
  • ercoerco Posts: 20,257
    edited 2016-06-17 16:21
    Video shows this chassis decked out 4WD.



    But I think my Boebot did hand tracking with more flair.

  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2016-06-17 17:16
    Didn't see the 4WD in many turns. That's the true test. Those tires look slim enough that they may not cause too much friction in turns.

    The wheels for 4WD are too far apart, though. Here's the eventual design I came up with for a 4WD buggy (dig that cwazy OOPic on the top!).

    http://www.budgetrobotics.com/manuals/rigel/rigel.pdf

    The tires are unique, and pulled for a dollar toy I found at Dollar Tree, when they were still selling decent toys -- those days are far over, sadly. They were a cross between rubber and plastic. The little hard nubs provided scant friction on smooth surfaces, so it could turn on a polished kitchen floor. But there was enough bite on sand and dirt for real off-road action. Note that the front and rear wheels are so close they are almost touching. Spread too far away, and it's like a tank with really long treads. Great for going through the Ardennes, but schreckliche for turns over high-friction surfaces.
  • ercoerco Posts: 20,257
    Rigel looks nice. In fact, I'm getting some ideas just looking at those close-coupled wheels/tires. Good traction, stability and maneuverability in a 4WD bot.

    Moderators: Can you say schreckliche in a family friendly setting? :)

    Selbstverständlich!





  • PublisonPublison Posts: 12,366
    Sounds harmless. :)
  • ercoerco Posts: 20,257
    Das ist nicht verboten?
  • ercoerco Posts: 20,257
    edited 2016-06-17 22:08
    Here's a small $6 line follower robot which uses a simple analog control circuit. Complete, cheap and probably hackable to add a micro. No reverse though, so plan ahead if you need an H-bridge: http://www.ebay.com/itm/371587727464

    http://www.banggood.com/Tracking-Robot-Car-Electronic-DIY-Kit-With-Reduction-Motor-p-972010.html

  • ercoerco Posts: 20,257
    I built my line follower kit, it works very well. It oscillates constantly since only one motor is on at a time. The two light sensor voltage dividers feed into the dual comparators, inverted, so they are never on simultaneously. Probably easier to adjust for contrast and varying light levels that way, especially since no instructions are provided! I might try adding a feedback resistor for hysteresis to see if that buys any smoother performance or just overshoot.

    I think this chassis has excellent hacking potential. In fact, it may be a "cheapest robot" candidate, allowing beginners to make a hardware robot to get some circuit-building and soldering experience before adding a simple micro to control it. Baby steps, Bob!

  • mindrobotsmindrobots Posts: 6,506
    You can be out the door for under $30 with a pretty powerful micro and a couple sensors to play with...even WiFi ready if you pick a nodemcu with Lua or micropython...pretty sweet!
  • Duane DegnDuane Degn Posts: 10,588
    One way of getting around the skidding issue with 4WD robots is to make two of the wheels omni wheels.

    Vex makes a lot of nice wheels. I like their 2.75" omni wheels.

    276-1902-omni-wheel_1_1.jpg

    (Sorry about using such a large image.)

    Vex wheels can be attached to metal gear CR servos with a bit of careful drilling.

    attachment.php?attachmentid=101674&d=1368933322

    Of course a set of 2.75" omni wheels is going to dramatically increase (by $20) the cost of the robot. If you're going to add a couple omni wheels you might as well go all out and use three or more omni wheels so the robot is capable of travelling in any direction.

    Each time I visit Vex's website I feel like the site has taken a turn for the worse. I used to be able to find their omni wheels with just a couple mouse clicks. Now is seems like they're hiding the wheels.
  • WhitWhit Posts: 4,191
    Duane Degn wrote: »
    Each time I visit Vex's website I feel like the site has taken a turn for the worse. I used to be able to find their omni wheels with just a couple mouse clicks. Now is seems like they're hiding the wheels.

    They keep moving in different directions...

    Sorry.

  • ercoerco Posts: 20,257
    Duane Degn wrote: »

    Each time I visit Vex's website I feel like the site has taken a turn for the worse. I used to be able to find their omni wheels with just a couple mouse clicks. Now is seems like they're hiding the wheels.

    No kidding! Now classic VEX is hidden under "VEX EDR". Requires five or more clicks to get from the VEX home page to this wheels page:

    http://www.vexrobotics.com/vexedr/products/accessories/motion/edr-wheels.html

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