All posts by Steve

AAPT Summer 2017 – PIRA Session on 3D Printing

3D Printing Allows for the Investigation of Real World Problems

Physics is one area that should be immune to the sentiment of, “When am I going to use this?” Yet I’ve heard this voiced in my class and to be fair I doubt many of my former students have ever needed to determine the flight time of a projectile launched in a vacuum or the speed of a hoop rolling down a ramp in their careers. 3D printing gives you the opportunity to either create or help your students create equipment to address engaging problems that go beyond the textbook. These problems might be the subject of national news or maybe just viral videos. In this presentation, I will share projects done by and with my students that benefited from the inclusion of 3D printing.

My Presentation as a PDF

Software I use for 3D Design:
Projects:
My Physics Models:

 

Tinkercad – More useful than you might think

For years my goto CAD solution for designing parts to be 3D printed has been Tinkercad. It really is the fastest way to get students designing their own 3D parts. The basics of Tinkercad can be taught with less than five minutes of instruction. Best of all, it is totally free and you don’t need admin rights to install any software..

The basic idea is that you create objects by combining primitives and then using other primitives to create holes or take away materials. The other thing to know is that once a shape has been added you can stretch or squish it in the x, y, or z dimension or rotate it around the x, y, or z axis.

Using this very simple paradigm you really can create some very complex objects. Creation of these objects often involves a lot of critical thinking and problem solving for students to figure out the best way to get to their desired final part.

Below is my take on the Spill-Not. A similar product is sold by science suppliers as the Greek Waiter’s Tray. This was created totally in Tinkercad in less than ten minutes. You can find my version on the Thingiverse.

Centripetal Motion Demonstrator

You can easily modify my version to suit what ever cup you might have. It currently will accommodate a standard coffee cup. To play with my design goto: https://tinkercad.com/things/i02pOyl5X81 and click on “Tinker this” (you must be signed in to Tinkercad first). Then click on Ungroup to reveal the underlying shapes. You might need to do this multiple times to see all the shapes. The order in which you group things has a huge effect on your final design.

The Centripetal Force Demonstrator was created from:
    • A “Cylinder” (orange) as the base with a squished “Torus thin” (red) to make a lip to keep something from sliding off.
    • A “Torus” (green) to swing it by. This was placed above the center of the base floating in space. It is important that this be centered above the base at the desired height. Then group it with the base so it will stay centered.
    • A “Torus Thin” (blue) was stretched and then rotated slightly to attach the base to the ring. “Box” holes were used to remove the un-needed bits.
    • A stretched “Half Sphere” was tacked on to the flat surface of the half torus in order to make the ring attachment more attractive. This is can’t be seen in the picture below.

Image showing the sales necessary to use in Tinkercad to create the Centripetal Force Demonstrator

TPACK and 3D Printing

Over the last several months I’ve been spending a lot of time thinking about 3D printing and learning. This was spurred on by the #MakerEDChallenge2 on the Thingiverse. The basic goal was to either create new designs that could be used as projects in an educational setting or to re-purpose old designs. In either case you were supposed to include a lesson description that goes with your thing.

Some of my entries were brand new things, but many were not. I realized that almost all of the things I’ve posted to the Thingiverse were created for some educational purpose. Many of these were for student centered labs or projects. However, I’ve only done a couple projects where I’ve had students designing and printing their own things (Wind Turbines, Phone Holder). So I thought about how I could turn some of my other designs into student centered 3D design projects and got a couple more entries together (Solve a Problem, Create a Device to Teach Physics).

Then I had a realization. Not all projects that involve a 3D printer need to be 3D printing projects. This revelation reminded me of TPACK.

Reproduced by permission of the publisher, © 2012 by tpack.org
Reproduced by permission of the publisher, © 2012 by tpack.org

TPACK is Technological, Pedagogical, and Content Knowledge. One of the main take aways is that we, in education, often look for ways to “Integrate Technology” into the curriculum. At best, this is sloppy thinking. At worst it can lead to lower outcomes. TPACK offers a different way of thinking.

Some of my education professors often said things like, “Content is King,” and, “Good teaching is good teaching. What works well in one area will work in any content area.” I believe thinking this way is just as sloppy as, “Integrate Technology.”

For me, TPACK starts with the idea of Pedagogical Content Knowledge. The idea behind PCK is that it is important to know the best techniques to use to teach your particular content. Basically, different ways of teaching will be better suited for different types of content. This seems obvious, but we often seem to forget it.

Specific pedagogies work better for specific content. I wouldn’t, for example, teach my electronics class the same way I teach physics. The content has some overlap, but all in all it is different enough that my entire approach needs to be different in each course in order to be maximally effective.

When we toss in the “T”, we’re saying the technology tools we have available give us new ways of teaching that simply weren’t available before. So rather than integrating technology for the sake of technology ask, “How does having a 3D printer in my room allow me to enhance old lessons or create new ones that would not have been possible before?”

With a 3D printer in my room, I as the teacher can create things that make it easier for students to ask and investigate questions that would have been:
My printer also gives me the ability to do projects with my students that let them:

Never ask the question, “How can I incorporate a 3D printer into my curriculum?” Instead you should think about, “What is possible now that a 3D pinter is in my classroom?” The distinction is subtle, but it is also powerful.

Fidget Spinners and the 3D Printed Rotational Motion Apparatus

Many years ago I saw a really cool apparatus invented by Steve Rea, a local physics teacher, for experimenting with concepts of rotational motion. It was a simple system of stacked pulleys of decreasing diameters. Metal rods with weights allowed the moment of inertia to be easily varied. The device was elegant in its simplicity and offered the opportunity for incredibly rich investigations and discussions.

As it turns out, Steve’s brother owns Arbor Scientific. Arbor adopted Steve’s design and they now sell it. Arbor’s Rotational Inertia Demonstrator works amazingly well and is very repeatable. I highly recommend it. At $160 cost really is quite reasonable for such a well built piece of lab equipment.

When I saw it for the first time I wondered aloud if I might be able to 3D print one. Steve told me I would have difficulty reproducing it because it was nearly impossible to find bearings that lacked grease. Grease is added to bearings to protect the metal bits from corrosion and increase the life of the bearing in high load/high speed operation. The viscosity of the grease in most bearings is too high for this sort of application. It would not allow for a good transfer of gravitational energy to rotational energy. Steve told me the hardest part of creating his prototype was finding suitable bearings. At the time I wasn’t interested enough to try to source acceptable bearings so I let the idea lay fallow.

Then, last year, the fidget spinner craze happened. Several months ago I was having a conversation about 3D printing with Andy Mann. He told me how his son designs and prints his own fidget spinners. Andy also related how his son is so into this he found a YouTube video showing him how to degrease his bearings to make them spin longer.

It took a day for the light bulb to turn on.  Two days after that I had a set of bearings from Amazon (I love Prime) and my prototype of a 3D printed fidget spinner. I started with this to make sure the degreasing worked and that I had dialed in the perfect size to hold the bearing.

With that done I knocked out a quick prototype, which failed utterly. Two versions later and I had it done. You can find my design on the Thingiverse and if you’re interested you can tweak it however you’d like in Tinkercad.

There are three different pulleys to provide different amounts of torque. With an extra set of hex nuts the washers can be positioned different distances from the center of rotation changing the moment of inertia. There are a lot of experiments that students can do to investigate rotational motion and the transfer of energy.

Rotation Demonstrator Side View

Diameters of the three pulleys:
    • 24.5 mm
    • 49 mm
    • 73.5 mm
Parts List: (about $10 in parts/device)
    • 2 each Skateboard Bearings, 608ZZ 8x22x7
    • 4 each 6″ long 1/4″ bolts
    • 12 each 1/4″ hex nuts
    • 40 each Fender washers, 1/4″ hole 1.25″ diameter (the number of fender washers can be varied)

Detail showing assembly

As I mentioned above, the bearings need to be de-greased first. The grease protects the bearings from water and road grit, but it will keep the bearings from spinning freely. I used acetone since we had it in the chemistry supplies. I just dropped them in a small beaker for 20-30 minutes. I found I also had to take them out of the acetone and spin them a couple of times then drop them back in. A lot of the instructions on the net direct you to remove the metal shields. I’ve found you don’t need to do this. However, if you get “sealed” bearings you will need to remove the seals. You need two bearings, one in each end, for full support.

If you want to avoid using acetone do a little googeling for other ways to de-grease bearings. There’s lots of stuff related to fidget spinners kicking around right now.

Square One Autonomous Innovative Vehicle Design Competition

Square One Education Network hosts a number of events every year. These include high quality Professional Development as well as student competitions. For the last three years our students have been competing in their Autonomous Innovative Vehicle Design Competition. The goal is to turn a Power Wheels Jeep into an autonomous vehicle. For this competition Square One provides the Jeep and also gives teams money to buy parts and supplies.

I’ll be documenting some of what my students have done this year here in this post. I’ll be updating this post with pictures, more details on parts, and all of the code (that will likely be after the competition)

Parts and Sources:

Things to Know/What we used these parts for:

You need some sort of a motor controller to allow your Arduino to regulate the current from the battery to the drive motors. We’ve used the Monster Moto Shield from SparkFun every year and it works like a champ. This will let you run the motors forward/backwards and give you a measure of speed control. You’ll need to solder on header pins and screw terminals, so be sure to order those at the same time. One weird thing we just discovered. We ran into a motor control problem last night that could only be solved by disconnecting an ultrasonic sensor from pin A0.  So, we’re avoiding pin A0 altogether for now.

The wheel encoders we found didn’t fit at all. The hole was too small, so students used a soldering iron to melt the rubber bushing to enlarge the hole. They then used a little superglue to affix the encoders to the really short shaft sticking out of the motors. Maybe next year we’ll be able to find some encoders that actually fit, but these seem to work for now.


The steering servo works well. If you buy one from ServoCity they offer to assemble the servo for an additional $30. I highly recommend you take them up on this. It’s not just putting the gear box together. It includes taking apart the servo itself and doing some modifications involving soldering and cutting a bit off a gear. I’ve bought two of these over the three years. This year we paid the $30. Totally worth it!


Our code is still being written. It will all end up in this Google Drive Folder when we’re done.

Playing with Programming

I’m teaching AP Computer Science Principles this year following along with the CS50 AP from Harvard. I like it, but this curriculum is way too heavy on the coding end to really match the intent of APCSP.

My plan next year is to mix and match Code.org’s material with ideas from CS50, but instead of C we’ll use JavaScript. With this in mind I’ve been playing with p5.js. I like it a lot for two very important reasons. First it gets students to graphics right away. It’s a lot easier to get student excited about code when they can create cool pictures on the screen than it is when all the do is print text.

The other thing I really like about JavaScript is students can run their code on pretty much any device with a modern web browser. As an example, check out the sketch below. I created after watching a cool video by Dan Shiffman. I made this in Openprocessing, a cloud editor for p5.js. If you’re interested, Wikipedia has a great explanation of the math involved in my program.

Paper Circuits

I’ve been teaching a semester long electronics class every semester since I started teaching in 2000. It started as a basic circuits course, but several years ago I started teaching it with the Arduino micro-controller platform. It has undergone several transformations over the years and I’m changing it yet again this semester.

We’re starting with some basic circuit fundamentals. In the past I assumed they would learn these fundamentals as we worked with Arduino. It turns out I was wrong. One of the circuit building things we did this week involved making paper circuits. This worked out really well and gave students a chance to discover differences between series and parallel circuits. They also got to do some trouble shooting to figure out closed, open, and short circuits.

All in all it was a fun project to help set the tone for the semester while also giving us an activity we can refer back to as we move forward.

Parallel Paper Circuit

Recommended resources:

Conductivity Meter for Chemistry Class

We have a new chemistry teacher this year. At his old school he used these conductivity meters from Flinn Scientific. He said they work really well. He had students use them to make qualitative comparisons of the conductivity of different solutions. The only problem I saw was their price tag. They are $22 ea. This is not horrible, but there really isn’t much to them. So I decided to see if I could make them cheaper.

Turns out it was pretty easy to source the components to place the cost at no more than $1.50 ea. So, for the price of one of Flinn’s meters I can make a classroom set.

I created a set of instructions for making your own:  Conductivity Meter Tutorial (PDF)

I used Plasq’s ComicLife to create this. I’d forgotten how much I enjoy using this for making tutorials.

Parts:

Cheap sensor help students answer real questions

I gave a presentation a couple months ago at the Spring meeting of the Michigan section of the American Association of Physics Teachers highlighting a project a pair of my electronics students did last school year. My students used an Arduino to read a 250g accelerometer to investigate the force a brain might feel in a violent football tackle.

From an Arduino point of view it was a trivial program. However, it was still a cool project for a variety of reasons. There were many opportunities for problem solving. They had to figure out how to embed the sensor in a meangingfull way, mount the helmet, and simulate a rough tackle. First task was determining how to mount the sensor. They asked if they could 3D print a head. This seemed reasonable to me, but I wasn’t sure if they’d have to design it or if we could find one. The head of Stephen Colbert was readily available and made us laugh, so that’s the one we printed after modifying it to accommodate the sensor. In retrospect this was not the best head to print as Colbert’s hair when 3D printed doesn’t squish the way real hair would. For this project it worked out fine, but for a side impact would not be ideal.

3D Printed Stephen Colbert in Helmet
I really like this project because it gave students a chance to investigate something of interest to them that is also very topical. As football players, this was of direct interest to them and something with wider potential impact as well. When they finished it I immediately wanted to share this project with other physics teachers. It would be cool to see other teachers working with their own students to do similar projects. However, whenever I try to show teachers how to use Arduinos to collect data, their eyes start glaze over as soon as the code hits the screen.

I decided to attempt to meet my physics colleagues where they are rather than where I am. Most of the physics teachers I know have access to either Vernier or Pasco interfaces and sensors. At our school we have Vernier, so that’s what I used. I assume you could do something very similar with Pasco equipment.  Vernier sells a cable you can use to make your own analog probeware. It turns out this was very easy to attach to our $30 accelerometer.

img_0322.jpg

The Black Wire goes to GND, the Orange Wire is +5V so goes to the VCC, and the Red Wire attaches to OUT. The other wires were not used. All you need to do is solder these three wires to the sensor and plug it into a LabQuest or LabPro. This is something pretty much anybody can do. However, if you’ve never soldered before I recommend this tutorial from SparkFun Electronics.

The 250g Accelerometer we used is an analog sensor. This makes it easy to interface with Vernier hardware. Nerd Alert: If you need to know, basically we are using it as a voltage comparator. On the LabQuest (or LabPro) we set up our sensor to read Raw Voltage (0 – 5V). For our sensor, zero volts corresponds to -250g’s, five volts with 250g’s, and at 2.5 V we have zero g’s. In reality the 5 V wire gave me 5.2 V (the USB standard is 5 V but can be up to 5.25 V or as low as 4.4 V), so zero g’s was at 2.6 V and 250 g’s would be 5.2 V. Since the output from this sensor is linear, I used the LoggerPro program to convert the voltage readings to g’s by creating a “New Calculated Column”. I ended up with a slope of (500 g’s)/(5.2 V) and a y-intercept of -250 g’s.

Screen Shot 2016-07-28 at 8.36.54 PM

The graph of my calculated column resulted in a graph of force vs. time. In the example graph below, the hit lasted for about 0.003 s and reached a peak of just over 63 g’s. Based on readings from the literature, a hit of this magnitude and duration would be unlikely to cause a concussion.

Football graph

With the growth of the Maker Movement there are now a lot of cheap sensors out there that can be interfaced in exactly the same way. Adafruit makes a 200g 3-axis accelerometer that looks promising, but you’d need 3 Vernier cables to read all thee axises simultaneously (also true with Vernier’s 3-Axis Accelerometer).  I’ve also been thinking about using some flexiforce pressure sensors to measure the force/area actually applied to the head in a collision. This would be a simple modification of this lesson on the Vernier site.

Iteration and Re-mixing with 3D printing

Just over a year ago I made a physics apparatus to help students develop a good mathematical model of acceleration. The idea wasn’t original to me, I just made it easy to make via 3d printing. My design works really well, but I wasn’t really satisfied with it. It consisted of a ring with two cones glued to the center of both sides. The side of the disk facing down always needed some clean-up prior to gluing. I let redesign ideas percolate in my brain to see if I could come up with something better. Then a couple months ago I saw a cool spinning top on the Thingiverse.

cd top

The two halves screw together and are sized perfectly to fit a CD. The instant I saw this I immediately knew I could do the same thing for my acceleration apparatus. All I needed to do was combine my idea with the nut-bolt bits from the top.

For me the ability to easily share, iterate, and re-mix existing designs  is where the power of 3D printing really hits its stride. I don’t have the CAD skills to make working screw threads and even if I did I wouldn’t have hit on using a CD as the disk. Since Gwo-Shyong Yan shared his design on the Thingiverse with a Creative Commons License I was able to not only find inspiration, but I could also build directly on his work.

After the inspiration came the iteration. Overall, I printed at least seven different versions before I was satisfied. I was trying to balance printability, usability, and overall appearance. When I was done I was pretty happy with the final design.

Of course, since I completed my original design more than a year ago I’ve already printed a full set of my old apparatus for the physics teacher in my school, so I really have no need of a new design. So, why did I spend several hours on this project?

There are really multiple reasons that all play into why I spent a Saturday working on this. I wanted to create a thing that other teachers could use with their students. I also wanted to add back to the community of Makers so that someone else might find inspiration to create something cool. But really I did this just to see if I could. I did it for the sheer joy of making a thing. That others might find this useful or interesting was really secondary. This makes me wonder, how do we engage our students to embark on things like this? How do we get them interested enough in doing a thing that they are forced to learn the bits they need to get it done? If you have any insights into this, or really any thing else please share them with me in the comments or via twitter (@falconphysics).

If you’re interested, you can find my final design on Thingiverse. You can also find links to my Tinkercad projects there in case you want to modify my designs.