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$27 OBO Mecanum Wheel RC Toy — Parallax Forums

$27 OBO Mecanum Wheel RC Toy

ercoerco Posts: 20,256
in Robotics
WOW, just found this and sent a $25 offer. Very cheap for a whole mecanum vehicle, you can't even buy the just wheels that cheap. Good toy and hopefully a good chassis to hack. https://www.ebay.com/itm/352817411944


Comments

  • ercoerco Posts: 20,256
    Or for the rich guys among us, here's a fancier one for $65 with a swiveling chassis and a tilt controller.

    https://www.ebay.com/itm/163895718120
  • ercoerco Posts: 20,256
    Or a wall-climbing RC car for $11... https://www.ebay.com/itm/283640341913

    Suction fan burns a lot of current to stick to the wall, FYI.
  • PublisonPublison Posts: 12,366
    erco wrote: »
    Or for the rich guys among us, here's a fancier one for $65 with a swiveling chassis and a tilt controller.

    https://www.ebay.com/itm/163895718120

    I'm showing @27.89.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    And shipping from China is FREE! Despite our staying in the Universal Postal Union, things will start to change next summer, it looks like:

    https://www.nytimes.com/2019/09/25/business/universal-postal-union-withdraw.html

    -Phil
  • ercoerco Posts: 20,256
    Somebody sure jumped on this deal! The seller just rejected my $25 offer so I had to pay full price ($28, gag me!) to get the last one of five this morning.

    @Pub: New ebay trickery afoot. They make it look like $28 until you click on the drop down list of multiple items and the item pictured costs way more. An accessory or completely different item is what costs the teaser price. Shameful!
  • ercoerco Posts: 20,256
    Barely cheaper, here's the bare chassis for sale with better color wheels: https://www.ebay.com/itm/283588545808
  • W9GFOW9GFO Posts: 4,010
    erco wrote: »
    Barely cheaper, here's the bare chassis for sale with better color wheels: https://www.ebay.com/itm/283588545808

    The wheels may look nicer but the rollers are conical. The first one looks to have properly shaped rollers.
  • W9GFOW9GFO Posts: 4,010
    erco wrote: »
    WOW, just found this and sent a $25 offer. Very cheap for a whole mecanum vehicle, you can't even buy the just wheels that cheap. Good toy and hopefully a good chassis to hack. https://www.ebay.com/itm/352817411944

    I was wondering why the video did not show the true capabilities of an omnidirectional vehicle. After reading the product description I now know why, the control inputs are not proportional;
    Function:1:Forward 2:Backward 3: Turn Rotation. 4: Left Rotation right. 5:Forward to left front at 45°. 6:Forward to left front at 45° 7:Forward to right front at 45° 8:Forward to left front at 45°. 9.Backward to left back at 45°。10. Back to Right back at 45° 11: Left sideward、Right sideward. 12:Dance、Music13: Auto Display

  • TorTor Posts: 2,010
    erco wrote: »
    New ebay trickery afoot. They make it look like $28 until you click on the drop down list of multiple items and the item pictured costs way more. An accessory or completely different item is what costs the teaser price. Shameful!
    Yep, common. You'll see it often when you search for an item and sort on price. First there'll be some sellers with a price of, say $7, then the rest follows with $31 or whatever. The first seller will use an option list where the $7 price is just something like a cover or useless accessory, and the other option is the actual item you searched for, at the normal (or higher) price.

  • ercoerco Posts: 20,256
    @Rich: Yes, at that price, I'm sure it's bang-bang non-proportional control. It remains for someone to hack this toy to show the chassis' full potential. Any thoughts? IIRC you have considerable experience in that arena, based on your amazing vehicle at Parallax's 2012 Expo:

  • W9GFOW9GFO Posts: 4,010
    Pololu has some $4.95 dual channel motor drivers that would work well. Get two of them and a Propeller and you could control that thing "properly".
  • AwesomeCronkAwesomeCronk Posts: 1,055
    edited 2019-10-15 11:33
    Were those vex meccanum wheels in that video?
  • ercoerco Posts: 20,256
    Yes, those are VEX wheels on Rich's lovely laser-cut plywood chassis.
  • W9GFOW9GFO Posts: 4,010
    Wow, it's been over six years?!

    Yes, Vex wheels with 3d printed adapters to mount them to the gearmotors.

    It is actually 1/4" MDF, since then I have found a good source for Baltic Birch so if I were to do it again, it would be plywood.
    Keppler.png
    1282 x 1326 - 3M
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    Hi all,

    Does anyone know of impellers that're functionally equivalent to Mechanum wheels for use in the water? It would be handy to be able to slip sideways against a transverse current without having to rotate the entire craft to compensate.

    Thanks,
    -Phil
  • W9GFOW9GFO Posts: 4,010
    edited 2019-10-15 22:34
    Are you familiar with the Voith-Schneider drive system? The animation on wikipedia is not correct, the blades do not suddenly flop over as depicted.
    This is the first video I found that shows how they work. I also do not agree with the wikipedia image that depicts the thrust vectors - notice that all the arrows point in the same direction, as if there were no drag. The foil at the six o'clock position should have the arrow in the opposite direction.

    There is one on eBay (for RC models) right now for a mere $380, free shipping!

    Aside from that, four paddle wheels with the paddles oriented at a 45 degree angle to the axis of rotation would achieve that. You would want the hull to be a shallow dish shape to so that it could move freely in any direction. Sounds like a fun project...
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    Thanks, Rich.

    So am I right to infer that the Voith-Schneider drive requires only two control inputs -- one for velocity and one for direction? Or are two orthogonal inputs required for direction?

    Given the mechanical complexity, it'd probably make more sense to buy rather than to build.

    -Phil
  • W9GFOW9GFO Posts: 4,010
    It requires two inputs for direction and one for velocity.
  • AwesomeCronkAwesomeCronk Posts: 1,055
    edited 2019-10-15 22:45
    W9GFO wrote: »
    Wow, it's been over six years?!

    Yes, Vex wheels with 3d printed adapters to mount them to the gearmotors.

    It is actually 1/4" MDF, since then I have found a good source for Baltic Birch so if I were to do it again, it would be plywood.

    Last year in school robotics I built a meccanum bot with the vex v4 system. I had no motor precision, though, and by the time I built the rest of the bot, I was burning servos.

    Oh how I wish our school robotics could be open-source!

    On the wheel subject, if one were to 3D print these, what materials would be needed for the rollers?
  • W9GFOW9GFO Posts: 4,010
    Here is a bit better price for the Graupner Voith Schneider drive.

  • W9GFOW9GFO Posts: 4,010
    AwesomeCronk wrote: »
    On the wheel subject, if one were to 3D print these, what materials would be needed for the rollers?

    Here are some ideas;

    Coat the plastic roller in Plasti-Dip.
    Stretch some vinyl tubing over the plastic roller - use a hair dryer to make it more pliable.
    Print using a flexible filament - dual print heads would be useful for this.
    Coat the plastic rollers in Goop - the glue, not Gweneth Paltrow's garbage.

    I am sure there are many more ways too.
  • AwesomeCronkAwesomeCronk Posts: 1,055
    Maybe I could wrap the roller in heat-shrink?
  • W9GFOW9GFO Posts: 4,010
    Heat shrink might be better than the 3d printed plastic but it would not be my first choice. Easy to try it out though.
  • robotsRcoolrobotsRcool Posts: 33
    Maybe 3D print the roller in plastic and use as a master to create a silicon mold. Then use the silicon mold to cast the final rollers in urethane. You might even be able to play with urethane of different hardnesses this way to see which one you like best. I came across this page documenting one way to do this.
  • ercoerco Posts: 20,256
    Mine arrived and works as advertised. Ordered on Ebay, but the package came from WISH.com, the bane of Internet shopping. The only real disappointment is they cheaped out on the battery. It's a tiny cylindrical 300 mAH Lipo which rattles around inside the large rectangular battery box, clearly intended for a larger flat battery. Also a PITA to recharge, you have to remove the battery (and battery door & screw) and plug it into a USB cable and replace. I'll have to do something about that.
    mecanum.jpg
    1440 x 2560 - 2M
  • ercoerco Posts: 20,256
    edited 2019-11-06 20:57
    Down to $17.66 from a US seller! Confusion fall! https://www.ebay.com/itm/352841506851
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