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Aug 06, 2013, 04:42 PM
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Rovers then & now

The optimum design for a cheap rover was basically discovered & proven in the previous century, but there's still money to be made in building new ones, I suppose.

Sphero was the most agile rover, but basically flopped after 2012. The startup didn't seem to capitalize enough on the social networking aspect of it or something that they focused on. You're not going to get very good teardown photos without buying one yourself, but it's a very standard electronics board.

Besides the world's favorite microcontroller, they didn't bother with a custom bluetooth solution, just whacking on a roving networks module. The difficulty in getting good wireless performance & the ruthlessness of product reviews probably justifies whacking on a 3rd party module. It has a full 9 axis IMU, an amazing investment just for 2D odometry.

That's your best view of the drive train. 2 parallel wheels do it all. It uses DC motors & encoders. There is a very difficult manufacturing problem in pressing the wheels on the ball.

No rover ever used stepper motors for odometry, probably because they're not efficient at low speeds. They're certainly simpler than fabricating an encoder. Modern RC cars use stepper motors, but only for efficiency at high speed.

Your best view of a 3 wheel adaptation of the sphero.

The next step down in cost & agility is the balancing robot. It trades a lot of manufacturing for electronics & is the most optimum use of the least amount of complexity. It still has a novelty factor. Odometry might not be as accurate, since it needs to move a little extra to balance itself.

The absolute cheapest rover is the 3 wheeler. Key to the design is a castor wheel. The castor wheel needs to freely rotate on 2 axes or it won't turn. The castor wheel can also jam.

None of these compares to the higher priced 6 wheel solutions that are used on Mars. Those are where all the ideas of the current century are appearing.

As tried & true as rovers are, there was still a time as a 5 year old when just getting a motor to spin with your own electronic parts was a miracle. You didn't care about the economics of it or whether it was beating on a dead horse.
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