Hitting the target every time: a high speed motion control/vision demo

August 05, 2010

Susan Rambo-August 05, 2010

Austin, TX: Maybe the Flying Dart Demo can go in the Totally Impractical Invention category, but it's a good demo for NI's motion control products. Like a midway game booth that's really good for your self-esteem, NI's Dart Demo shown at NI Week 2010 uses motion control and high-speed cameras to make sure the Nerf dart you've shot always makes it to the target. How do they do it? They move the target. Of course.

Nerf darts travels over a 4-ft span in less than 100 mSec to hit the target. To get an idea of what the demo does, you can watch an extremely short video here (but longer than 100 mSec) or for longer videos, including the keynote demo, go to Sisu Devices' web site.

The demo basically has two high-speed cameras that take nine pictures after the dart enters under a special reflective hood. A stereo camera algorithm triangulates the XYZ position of the flying dart in 3D space. The first picture has a flash that isolates and locates the bullet on a white background (the metal) the first time, sending that data to the industrial controller. The NI industrial controller handles the processing of the images and sends the instructions through the EtherCAT AKD drives, which control the motors. The conductive mess sensor on the target senses when the dart hits and triggers an appropriate richochet sound depending on the sound mode (Star Wars, Rocky, or the cowboy theme). For a better explanation, see how the engineers describe the system.

NI hired Sisu Devices, an Austin, Texas-based motion control and automation company to design and create the demo. Two engineers-–a mechanical engineer and a systems engineer--worked on the project over six weeks. Engineers Russell Aldridge (mechanical) and Marc Christenson (systems) supplied NI with the concept and computer animations. Once the concept was approved, the engineers ran motion simulations in SolidWorks to figure out the torque and load conditions. The simulation was an interative process: the length of the arms had to be adjusted several times. The engineers spent a week in simulation, running finite element analysis, after which they could then spec the components (with NI's approval). (For component list and other info, go to Sisu Devices). The Sisu engineers also used NI's SoftMotion 2010 to integrate the motion control components, and the demo shows off NI's new TimeSync, which synchronized the two time stamp readings used to determine the speed of the dart.

The next week was spent in CAD, getting things right; followed by another week in the machine shop and plastics fabricator (the hood was fabricated by the Sisu team themselves). After that, it was tweaking the system and getting ready for the show.

Obviously the demo is a custom application (not being mass produced—after all we'd get bored winning all the time); it is a graphic example, however, of the state of the art if such a complex system can be now made in six weeks start to finish. Bravo.

Susan Rambo is site editor for the Industrial Control Designline and is managing editor of Embedded Systems Design magazine. You may reach her at

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