Stewart Platform Ball Bearing Balancer

PID balancing a ball on a plate

For their Mechanical Engineering senior design project at San Jose State University, [Tyler Kroymann] and [Robert Dee] designed and built a racing motion simulator. Which is slightly out of the budget of most hackers, so before they went full-scale, a more affordable Arduino powered Stewart platform proof of concept was built. Stewart platforms typically use six electric or hydraulic linear actuators to provide motion in six degrees of freedom (6 DOF), surge (X), sway (Y), heave (Z), pitch, roll, and yaw. With a simple software translation matrix, to account for the angular displacement of the servo arm, you can transform the needed linear motions into PWM signals for standard hobby servos.

The 6 DOF platform, with the addition of a resistive touch screen, also doubled as a side project for their mechatronic control systems class. However, in this configuration the platform was constrained to just pitch and roll. The Arduino reads the resistive touch screen and registers the ball bearing’s location. Then a PID compares this to the target location generating an error vector. The error vector is used to find an inverse kinematic solution which causes the actuators to move the ball towards the target location. This whole process is repeated 50 times a second. The target location can be a pre-programmed or controlled using the analog stick on a Wii nunchuck.

Watch the ball bearing seek the target location after the break.

Thanks to [Toby] for sending in this tip.

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DMG Lib: Digital Mechanism and Gear Library

Reader, [klemens], suggested DMG Lib to us when we posted about a similar site. DMG-Lib is an amazing source of information. It’s primary downside is that a great portion of the text is in a language other than English, though in some ways this is a plus. Latin, Italian, German, and many other languages held the position of being the chief scientific language of the world long before English, and this repository holds entire books about mechanisms in those languages. Some of the books range all the way back to the 1500s. The mechanism animations are very good on this site and play smoothly. While it’s a little harder to search than KMODDL due to the language oddities, it’s still an extremely useful and interesting site to add to the hacker’s information toolbox.

KMODDL: A mechanism maker’s dream site.

Computers are relatively new still, but we’ve had mechanics for a very long time. KMODDL  keeps us from reinventing the wheel. It contains collections of mechanisms with descriptions, pictures, and even videos. We were working on a arbalest design not too long ago, and we were having trouble coming up with a clever ratchet design for one of the parts. We spent a few moments in KMODDL looking through the ratchet section of the Reuleaux collection, and  soon after we had the basic building blocks of our design. Sure there are books you could buy that do a similar thing, but KMODDL is completely free, very in depth, and easier to search. Plus, with a useful tool like this you might not even have to take apart all your appliances anymore to see how they work. My first sewing machine might have lived a longer life had I seen this first. Anyone know of more resources like this?

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