Tuesday, December 16, 2014

A Drone with two Rotors and no Swashplate

In order to be able to maintain attitude, a UAV or drone must be able to alter its rotors in some manor to create roll, pitch, yaw (for rotations), or linear motion in any of the three directions. Four rotor devices (quadcopters and tri-quads) do this by alternating the rotation of their props, and then changing each motor speed to attain directional or angular movement. Three rotor devices (tricopters) do this through the use of three props, with the angle of one of them controlled by a servo. Helicopters and other two rotor devices make use of a swash plate on one or both of their rotors.

The guys in the YouTube video above have devised a rotor mechanism that will react to changes in the torque of the motor upon the prop. The technical description is that they phase modulate the motor speed with respect to the other rotor. This, then, induces a change in the pitch of the rotor blades. Check out the video and then go here to check out some of the other devices they're making at UPenn.

Saturday, November 15, 2014

This Music Video Has it All!

The song is titled Cymatics by Nigel Stanford. Cymatics is the study of visualizing vibrations. It has a Ruben's Tube, the Chladni Plate, Ferro Fluids, a Tesla Coil, and a Plasma Ball!

Nowadays, rather than use sand, liquid, or fire to visualize vibrations, we use accelerometers and microphones or even lasers to measure the actual vibration and sound. We then use advanced software to overlay those measurements onto a model that we can manipulate on the computer.

Here's the original Link to the io9 site that has all of the videos. You can download the entire album, titled Solar Echoes, here. Enjoy!

Tuesday, October 7, 2014

And the Winner is...

Today the 2014 Nobel Prize in Physics goes to Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura. Don't be surprised if those names aren't familiar, because what they did to earn a Nobel Prize was done about 20 years ago.

Even if their names aren't common, their invention is very common now. They are the inventors of the blue light emitting diode (LED). This, now is a truly amazing innovation for many reasons. For years red and green LEDs we very common, but creating blue was ever elusive. In order to make white light, all three colors (red, green, and blue) are required to create white light. What that, then, allowed is the ability to create a very low power white light, and white light bulbs. Not only that, but that also allowed is the invention of the RGB LED, and the RGB LED addressable panel. These inventions allow for awesome creations like this!

What does this have to do with Dynamics? Not a lot actually, but if you're interested in the science of crap in motion, then you are probably interest in this as well!

Monday, September 22, 2014

Lambda Top Spins for almost 10 minutes...

This ridiculously smooth top utilizes an instrument grade ruby (now also a stainless steel BB) to create a nearly perfect point on which the top can spin. From the Kickstarter:


This equation is all you need to know about tops. For a given top, the size (radius) and weight (mass) are fixed, so your only variable is velocity. If you want more spin, you need more speed. How fast can you spin it? The (major) factors that reduce spin time are friction and the geometry between the top's "contact point" and the target surface. You get to pick the surface, but I get to pick the contact point :)

The other nifty aspect of this little toy is that is that it is optimized to have a lower polar moment, while still having a large mass to maintain momentum. Back to the Kickstarter


6061 aluminum is used for the spindle to decrease the polar moment of inertia...in other words, reducing the amount of force it takes to get the top up to a given velocity. If you remember, the more velocity the more angular momentum...and a longer spin time.

Solid brass is heavy, really heavy. It also machines beautifully. If you recall, mass is another important component to angular momentum, making brass an ideal material for the outer ring.

This all adds up to a top that spins for a ridiculous amount of time. up to 12 minutes in fact, however the video above is about 10 minutes of spinning.

Monday, September 8, 2014


The video shows a research project at ETH Zurich called Cubli. It takes advantage of reaction wheels, in several unique ways. Typically a reaction wheel is used on an orbiting space craft in order to maintain attitude. Basically they are a type of flywheel that is continuously spinning. A change in angular speed/momentum of the reaction wheel results in an adjustment of the craft, due to the conservation of angular momentum.

Cubli takes this to the next level. Spacecraft are typically outside the effects of a large gravitational pull, and angular corrections are calculated only in the inertial frame of the craft. Cubli is working within another inertial reference frame, so all of its attitude adjustments must take into account that frame, that is gravity. Watching the video you can see the reaction wheels spin up and then quickly brake in order to bring the cube first up on edge, then on its vertex. The positioning of the cube is maintained using the reaction wheels, and the reaction wheels can also be used to control the direction of the fall, creating a "Walking" action.

There are more videos after the break, as well as a couple other pretty awesome projects at the Institute for Dynamic Systems and Control at ETH Zurich.

Monday, September 1, 2014

Sound Mirror

This one is a little bit of acoustics and a little bit of calculus. The British military experimented with acoustic detection of approaching aircraft. These parabolic concrete plinths (Called Sound Mirrors) were built as the predecessor to radar during World War I. Many mirrors can be found on the coasts of England, and many more would have been built but for the invention of radar

The concept of operation is that a listener or microphone would be placed at the focus of the mirror. Due to the definition of a parabola, all sound coming from long distance (infinity) would reflect off of the mirror, and be directed toward the listener. In effect, this is a very simple means of amplifying and detecting plane engine noise from long distances. Similar equipment (albeit more compact and portable) is still used today as a means of spying on people or listening to the sounds of the NFL

This exhibit at Brooklyn's SIGNAL Gallery is a recreation of these mirrors with microphones embedded in their center. Two such mirrors are facing each other to create an interactive experience in the large gallery space. The sound picked up by the microphones is then played throughout the space via speaker.

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.