Category Archives: 3dprinter

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.

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.

Learning with OpenSCAD

I’m currently teaching a class to pilot AP Computer Science Principles (will be AP for the first time in the 2016-17 school year). At the beginning of the second semester I decided to deviate from my planned curriculum and drop in a little 3D printing. I had students play with OpenSCAD. OpenSCAD is used to create 3D models with programming rather than more traditional means.
 OpenSCAD is really cool for a number of reasons. If students have any experience with writing code they can dive right in. They quickly realize there are many different ways to create the same part, just as there are always multiple ways to get any program to do what you want it to. Most of these ways will involve thinking in 3-dimensional coordinates while also thinking about positive and negative space. Depending on the chosen approach students may also need to bring in a variety of mathematical knowledge and skills they’ve developed over the years.

The task I gave my students was to develop a stand/holder for their own cell phones. It took them a bit to settle into this idea. I kept getting questions like, “Do I need to plan for a case?” To which I’d reply, “I don’t know, does you phone have a case?” I really wanted them to plan for a holder for their own phone.

In the future I’ll need to put some limits on their designs. Most designs were much bigger than they needed to be, many would easily hold an iPad. Maybe I’ll put a limit on the mass of plastic they could consume. I also need to make sure their design will fit the printer. I had one that would not.

After printing their stands they all realized there were problems with their designs, things that were not obvious before they tried using the physical objects. This was a great lesson and gave us a chance to talk about rapid prototyping and iteration. Each student shared their first designs with the class so everyone could learn from each other’s mistakes. The designs were then updated to fix the problems. In the redesign I also had students add in variables for phone size. This would then allow the program to be used to make a holder for any phone by simply changing the values of the variables for phone height, width, and thickness.

Overall I really liked this assignment. Students got to use their programming knowledge in a new way with a new language. I personally delivered no instruction in OpenSCAD. Students had to rely on the principles of computer science they’d already learned, tutorials found on the net, and each other, just as they would in the real world. The task was simple enough that I knew this would not be a problem. I will be doing this again as a planned part of the curriculum next year, but I’ll add in design constraints related to size and total cost of materials.

Tutorial for an Arduino RC Car?

A buddy of mine recently sent me a tweet:

RC Arduino Tweet

This is an interesting question the short answer I have is, “No.” The longer answer is a bit more nuanced, so I asked for a little clarification. This is what I got back:

RC Arduino 2

Now I had a lot more to go on. With this in mind I have something to sink my teeth into. Now we have something, so now my response is, “No, I haven’t seen anything that would fit.”

OK, now that that’s out of the way lets cover how I would tackle this problem. Tony is an awesome math teacher in Zeeland, Michigan. He co-teaches a project based math/physics class. I’m going to work from the assumption that he’s working with students starting with little previous knowledge of electronics and Arduino programming, and that he’d like to leave as much room as possible for students to explore. Everything I cover will be with that in mind.

With a project like this you need break it up into pieces. I’m going to think of this as a robot even though it won’t be autonomous because we still will have a computer controlling an independently moving device. As with any robot type project you have three fundamental challenges, the programming, the electronics, and the mechanics. However, with this project we’ll need to consider a forth part I don’t usually think about with a robot, and that is the control mechanism.

Mechanics

You could go crazy with this and start with a platform like Tuggy from the very cool OpenRC Project. While totally awesome I think this takes all of the thinking away from the students and simply turns them into mechanics. Which is fine if that’s your goal. Instead I’d start with ThinkFun’s MakerStudio collection of building sets.

macaroni box car

You can buy sets or download and print from the Thingiverse. I’d start by having students play with the gears and such and make simple cars with parts available, then begin thinking about what their RC car needs. They’ll need to make a variety of decisions. How will their cars be steered? Will they use skid steering (like a tank) or rack and pinion (like a car)? What sort of  platform will they need? I’m not sure a Mac & Cheese box is the best choice. How many motors will they need? Will they use gearbox motors or simple DC motors and then use the gears in the set? Some of these decisions might be made by the teacher and some or all might be left out the students. I’d probably go with simple DC motors and use the gears from the set.

Once these decisions have been made students can then think about the parts in the MakerStudio kits they don’t have but need. Things like motor mounts, rack and pinion mechanisms, bits to mount the gears to the platform of choice, and such. These could should all be designed and 3D printed by the students.

Electronics

Tony asked for Arduino, so we’ll stick with that. It also doesn’t hurt that I know a lot about using Arduinos with high school students. Unfortunately, you can’t run any sort of reasonable motor directly from an Arduino. You need some sort of transistor or h-bridge. Digital outputs on your Arduino only put out 40 mA, this is woefully inadequate to power a motor.


Students can wire an h-bridge themselves, but I highly recommend using a motor shield. I’ve had many students use an h-bridge and breadboard their circuit which mostly works. There are a lot of connections that need to be made and by the time students got to soldering stuff together numerous problems would typically crop up. In order to get around a lot of headaches I now have students use motor shields and skip all the complex wiring. You can buy shields from China really cheaply, but I like to use SparkFun Electronics. SparkFun is based out of Colorado and they offer an educator discount of 20% and allow you to easily set up payment accounts allowing you to pay via purchase order. The other thing I really like about SparkFun is that they include code example and/or tutorials for almost everything they sell. So I can hand a shield to a student and then point them to the product page and step back.

Most motor shields will allow you to control two motors, perfect for skid steering. If your students chose to go with rack and pinion then you can get away with one drive motor, but you’ll need a servo-motor for steering. There are lots of tutorials for controlling servos with Arduino and ideally where ever you get your motor shield will tell you how to wire your motors to it and give you a simple program to control your motor(s).

Other Stuff

At this point we just have programming and control mechanism left. I have some ideas about control mechanisms, but I haven’t done any of these in the past. When I say “I” that really means my students. So, I’m going to do a little more research and then another post. More than likely I’ll be looking at some sort of the cool BlueTooth module and an app running on a cellphone or tablet. There are other ways, but controlling a robot with your phone is just too cool.

Apparently I’m a Total Nerd

So today I’m geeking out a bit. The school’s 3D printers are in another room on the other side of the building from my office. If you’ve ever used a desktop 3D printer then you know they have a tendency to fail. This can be a problem when you are not near the printer. A while ago I figured out that I could use a cheap webcam and stream the operation of our printers live to YouTube. It’s not riveting video, but it lets me keep an eye on things. However, when things go wrong I still have to run down the hall to stop the printer.

Enter Chrome Remote Desktop. This lets you use Chrome to remotely access a computer that you are signed into. It’s pretty easy to set up and I can even access it from outside of the school building. If I use the same computer that is running the 3D printer I can cancel the print job remotely. This means I could start a long print job and still monitor it from home. If things go wrong I can stop the printer from making a pile of spaghetti.

Presentations for Mercy TechTalk

I’ll be giving to presentations today at Mercy Tech Talk. Here are the links from my presentations:

3D Printing in Education – 11:10 in N-17
Curious about 3D printing? We will walk through the basics of 3D printing and introduce simple programs for creating 3D models suitable for printing. No previous 3D modeling experience is needed. We will also look at some ways 3D printing can be worked into the curriculum and for fundraising.

Flipping with an iPad – 1:00 in Drama Studio
Have you thought about making videos to support your instruction? Maybe even a full flip? With an iPad you can create and distribute videos for your students. We will investigate several apps and accessories you can use to make compelling content for your students without the need for a computer.