Saturday, August 23, 2014

Stewart Platform Ball Bearing Balancer



A couple guys at San Jose State University, as a precursor to a racing motion simulator, have built a Stewart platform. This is a special type of robot that allows motion control in all 6 axes: linear motion laterally, longitudinally and vertically, as well as rotation in roll, pitch, and yaw. In the video you see a flat table with a resistive touch screen (to determine the current location of the ball) brings on memories of the Classic Nintendo game Marble Madness

This small demonstration displays two disciplines of classical mechanics, control theory and kinematics. Control theory is a sub-discipline of dynamics that applies to many aspects of everyday life. Thermostat/HVAC systems, cruise control, and any application where a feedback sensor of some sort is used to determine the next behavior of a control on the overall system are all examples. In the case of this Stewart platform, the resistive touch screen is sharing its information with an Arduino, which then calculates the proper position of the six servo arms to maintain the balls position. Kinematics (a sibling to dynamics) is used to solve for the positioning of the servo arms.

More information on this this particular setup on Hack-A-Day and Full Motion Dynamics!

Wednesday, August 20, 2014

Figure out which coin I dropped by the sound of its fall...



Coins are great devices used in a lot of different Dynamics problems, mostly because they are fairly easy to model and solve analytically. This however was once I hadn't seen anyone put a lot of time into before.


Ohk... So the actual question asked at this Physics Forum on Stack Exchange reads a little different. However the results answer my question much better. Each coin, having slightly different mass and stiffness characteristics, has slightly different resonant frequencies. Dropping a coin is very similar to performing a modal impact test. A coin, being almost completely flat surface, is a very good radiator of sound. The spectra shown above show different peaks that are indicative of the resonances (for indeed, most structure have multiple natural frequencies of vibration). Each of these peaks has a characteristic motion for the coin. This motion is called a mode shape, and flat panels and coins are very well understood geometries where this can be analyzed.

Sunday, August 17, 2014

So I'm a slacker...

And haven't posted in over a year... Here's a little spotlight of what I've done in that year:

I spoke at a bunch of different trade-shows talking about about everything from microphone selection to sound power. I have more talks coming up on automotive cabin interior noise (Auto Test Expo), acoustic calibration of microphones, and designing and building an anechoic test chamber (International Modal Analysis Conference).

I did onsite testing of some of our accelerometers for Hendrickson International and Rolls Royce. Both of these instances allowed me to travel to pretty awesome places, and be a part of some pretty neat dynamics testing. Hendrickson was a durability course where I actually rode in the sleeper of the cab while driving a semi with trailer over a ridiculous amount of bumps and road cracks. Rolls Royce was a simple every day jet engine balance test... :-D

I traveled to Pretoria, South Africa to talk with electroacoustics experts from around the world about the standards surrounding microphones, sound level meters, artificial ears, and various other acoustic measurement implements.

Meanwhile, when I'm actually in the office, I've been working on updating our procedures of microphone calibration, including free field, pressure, and random incident calibration. These three calibration types are mostly complete, and my next big project is performing a reciprocity calibration of microphones. My couplers are in house, I just need to sit down and do it!

I'll try to keep this up a little bit better. Sunday nights seem like a good time for me to do this, so watch for updates.

Keep an eye on a couple other pretty awesome sites for various engineering badassitude. These include:

Fuck Yeah Fluid Dynamics!
Smarter Every Day

I'm going with Nicole's model on FYFD and only doing short talks on stuff. I was getting way too long winded with my updates, and was boring myself.