Tricycle robot using omni-wheels

[Markus Gritsch] built this six-wheeled robot using omni-wheels. Two wheels are used on each axis in order to ensure perpendicular rotation is possible no matter where the axis rotation stops. The wheels have also been improved by dipping the elliptical components to give them a rubbery coating.

The robot gets its commands wirelessly from a separate controller unit. That controller, as well as the bot seen above, uses a Teensy microcontroller board. Two analog sticks take input from the operator and transmit commands using an inexpensive RF pair. The wheel movement is facilitated by three servo motors which may seem like an odd choice. But we think that it simplifies the electronic side of the build because you do not need an H-bridge to control a servo motors. It’s a bit loud, as you can hear in the video after the break, but it certainly works quite well.

One of the commenters on the thread above asks why [Markus] didn’t use mechanum wheels. These would have allowed him to use just one wheel on each axis but the omni-wheels were so inexpensive that he went this route instead.

Comments

  1. Brian.Holiday says:

    I would lay odds he didn’t ‘dip’ the wheels (He doesn’t say how it is applied). I have tried dipping and it doesn’t give acceptable results for rubberizing wheels. Plastidip has a spray on version of their coating which works quite well.

  2. ino says:

    very nice!

  3. eddt says:

    Not the first one of these I’d seen – http://the-gadgeteer.com/2001/03/28/palm_pilot_robot_kit_pprk_review/ . Back in the day, you could get them as kits from http://www.acroname.com . Still, a really nice build. I wonder if he modded the servos himself.

  4. DeadlyFoez says:

    I like it. Good job.

  5. Soo-Hyun says:

    I’m not sure how he could have used mechanum wheels for this platform, since they are used in pairs to generate movement parallel to the wheel’s axis. I guess it could be done with some careful programming, but mechanums are (afaik) used in pairs.

    Those are also single wheels even though they have two layers. The rollers are just offset. I’ve used Kornylak Transwheels (http://www.kornylak.com/wheels/transwheel.html) for my triwheel robot.

  6. wosser says:

    I like the smoothness of the motion, and the wireless gamepad controller is a cool.

  7. Markus Gritsch says:

    @Brian.Holiday: Yes, I used the spray (http://www.conrad.at/ce/de/product/888183/PLASTI-DIP-SPRAY-311G-SCHWARZ/SHOP_AREA_19752&promotionareaSearchDetail=005)

    @eddt: Yes, modifying servos for continuous rotation is not hard. Just make sure the potentiometer is mechanically not connected to the rotating wheel anymore.

    @Soo-Hyun: Although you need pairs of wheels, they are sold in single quantities (http://at.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=0408536). I glued them sogether using superglue :)

  8. psuedonymous says:

    Mecanum wheels require a minimum of four wheels to move omnidirectionally. Their advantage being that they can be mounted in existing chassis with normal wheel placement, where omni-wheels need a triangular arrangement for full holonomic movement.

  9. john_austin_tx says:

    Thank you for sharing this wonderful project. It is inspiring to me :-)

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