Omnidirectional Remote Controlled Robot

[Markus Gritsch]

Recently, I got interested in omni wheels, so I built this little robot. The robot has three pairs of omni wheels. I covered each roll of the omni wheels with liquid rubber (plastidip) to get better traction. I bought the cheapest servos I could find and modified them for continuous rotation. The robot is powered by four eneloop NiMH batteries and controlled by an Arduino nano 3.0.

The remote control itself uses two analog sticks which control the three axes of freedom (forward/backward, left/right, turn clockwise/counter clockwise). A Teensy 2.0 continuously reads the analog values and sends them to the robot via a simple custom serial protocol which is transmitted using on-off keying (OOK). A pair of transmitter and receiver costs $4.90 at seeedstudio. The Arduino on the robot receives these values and calculates the corresponding rotation velocities for the three servos.

A video is available here: http://www.youtube.com/watch?v=e3SJlshwl6k

For the future the robot could be modified to read some sensor data to drive also autonomously.

[Markus Gritsch]

Some more pictures.

[arhi]

you might be interested in: http://www.thingiverse.com/tag:Mecanum

[Markus Gritsch]

Thanks arhi. Yes, I read about the Mecanum wheels, but they were quite expensive to obtain. I bought the omni wheels for €3.90 each.

[arhi]

The reason I ended up with RepRap project (I'm even in the core team :D ) is because my main hobby is robotics and it was very expensive for me to acquire proper "parts" for my robots (different holders, brackets, wheels) .. so searching for a solution I came to RepRap project (http://reprap.org) .. for a fairly low amount of money you get 3d printer that prints those mecanum wheels in one night with cost close to nothing :D .. not to mention other cool stuff you can print for your robots :D ... just a thought :)

[ChrisGBG]

Very neat, I got the exact same wheels and I'm wondering what you used to fixate them on the axle? I just see something white and screws? Did you try the wheels without the plastidip? Did it slip a lot?

[Markus Gritsch]

The "something white" is a normal servo wheel directly screwed to the omni wheels. Didn't try without plastidip.

[ChrisGBG]

Ah, at that scale I guess bolting a servo straight to a wheel works really well, my robot is a fair bit bigger and heavier and has motors + gearboxes with a very awkward and weak axle, hence why I'm trying to figure out a strong way to mount the wheels to a supported axle which in turn mounts to the gearbox axle, though frankly I'm starting to wonder if ditching the motors and gearboxes and going for something that has self contained support isn't a better idea.

Here is my current design:

http://cl.ly/image/3B2x2F1U410a

http://cl.ly/image/320L2e0N162G

http://cl.ly/image/0w3M2P432Y2V

tried img tags but they didn't resize properly only showing a tiny part, it has some pretty large pit-falls, like the axle adapters http://www.dfrobot.com/index.php?route= ... uct_id=645 that connects to the gearbox http://http://www.dfrobot.com/index.php ... uct_id=100 (same design except straight instead of bent) only way I could figure out to marry the M8 bolt "axle" of the wheels is gluing a nut to the end of the adapter, which ofc means I'm relying on glue to hold a rotating axle, and a nut on a rotating bolt... I'll have to locktite it. I'm not confident at all.

Advice would be greatly appreciated except "get a 3d printer" :P they don't grow on trees you know.

[ChrisGBG]

I just did a very quick and rough assembly... and well... it works kinda, the wheels without any plastidip or similar on a wooden floor slip and slide a ton and my tiny DC motors with not much down-gearing in the gearbox spin way too fast, the robot moves in the expected direction reasonably well, but it's basically spinning at least 4 times the distance is moves if that makes sense, and since it has 4 wheels with no suspension or give what so ever going over anything makes at least one wheel free-wheel in the air.

And this is without the 300g battery, motor controller boards, arduino mega and second level on top, I expect the performance to get even worse with that weight on top.

I'm re-spinning the design, going down to 3 wheels and switching to a "medium" sized servo with lower gearing for power on the inside of the wheel, and a bearing block on the outside for more support, the design is pretty much a triangle with a flattened corner and a wheel fairly close to each corner, wheels going through the triangle in holes just big enough, axles on the underside the 6mm plexi base, this way I can use a servo horn like you have for rotation, and an axle going through the wheel and into a bearing block on the outside for more support, axle doesn't have to marry at all to the servo, it's just there to support the wheel and hold it sideways.

I'll need to find something like plasti-dip to coat the rollers with as well, clearly needs more traction.

Quick sketch http://cl.ly/image/1x3y0A2u1X19