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This photo was taken near here
Wow:

Dr. Tom Bensky
Professor of Physics
and
Department Scheduler

Cal Poly Physics Department
Office: 25-215
Phone: 805-756-7655
Fax: 805-756-2435
email: tbensky@calpoly.edu

Teaching

I like tinkering with teaching and am always looking for new ways of injecting modern ideas and technology into what I do. Here is some of my work.

Class attendance

I coded up an attendance system called Youhere.org that allows teachers to take attendance by having students "check-in" to class using their location-aware phones. Check it out!

Arduino

As you probably know, the Arduino is a hugely popular microcontroller. A while back, as part of our 'advanced electronics' class (PHYS 357), I started using the Arduino as the core of a data-logger project. In this project, students would choose a sensor (from dozens available, like temperature, pressure, etc.) and interface it to an Arduino. They would then also interface the Arduino to an SD-Card module, and program it to log readings from their sensor, to the SD-card, for later analysis.

Construction of the data logger aside, the most creative element of this project is in allowing the students to decide how and where to deploy the data-logger. I've seen students take it on hikes, attach it to their cars or bikes, take into exercise classes, and even put it on a horse saddle while riding.

I've come to like this project because taking data in an automated fashion (i.e. no paper, stopwatches, yardsticks, string, tape, etc.), retrieving the data, plotting the data, then coming up plausible 'story' to describe the data is to me, the epitome of what a scientist does.

I have found this project to be remarkably adaptable to a variety of audiences. Currently, I've done it witg advanced physics majors, high school juniors/seniors, and freshman Liberal Studies majors.

Here are copies of my core lessons (thank you M.M. for proofreading these). These were run over 4 class sessions, using about four hours of class time, culminating in a lesson on how to make a proper plot (title axes, etc.) and a presentation to the class on the results (i.e. the 'story' behind the data).

The culminating event is when each group presents their project to the class. At all levels, I am always pleasantly surprised by the creative (and sometimes crazy) scenarios students find for their data logger---and most of the time, I don't know the details until their presentation. (A photo of their data logger "in action" is required in their presentation.)

Prolog and Symbolic Processing with Kinematics Problems

If you look carefully at physics problems in an introductory physics book, they can all be solved algorithmically. That is, if you simply find or compute quantities, in the right order, using either 1) common sense, or 2) the equations given in the book, you'll get the correct answer, every time. You just have to find that 'right order.'

This paper I wrote a while back discusses this in the context of 1D kinematics problems, involving only one moving object. Here is the code for it, if you want to investigate it further.

3D Printing

3D Printing Gotchas

No matter what brand of 3D printer you buy, it won't always work.

Material Purge

If it bends upward, increase the nozzle temperature in 5 deg C increments.

Build Plate Temperature

Glass at 80C

Build Plate Leveling

A piece of paper between nozzle and printbed should require a moderate amount of tugging to extract. You want that first layer to be squished and flattened onto the build plate.

Introductory Mechanics

Online homework assignments

Introductory Electricity and Magnetism

E&M tends to be a very "mathy" course. Thus, I started to use Sagemath (now CoCalc) in this class to help us wade through the math. Here are some of my activities using CoCalc.

Longitude, Time, and Navigation (ASTR 324 here)

Electronics (PHYS 206 here)

Most of what I know about electronics was self-taught by reading everything I could find by Forrest Mims and building circuits in my garage with stuff I bought at Radio Shack or here. I find Mims' hands-on, active and "circuits that do something" approach goes quite far for both teaching and learning electronics. I think this book is one of finest introductory books on electronics ever written.

I put together the core of these labs (C. Hoellwarth and M. Moelter helped a great deal to get these labs in shape) to cover our 10 week electronics class.

Advanced Electronics (PHYS 357 here)

I started running this class in "project/makers" mode in Spring 2011 and continue to do so. Here are the three projects students are to do over the course of the quarter.

I thank my colleague Matt Moelter for his help in refining this curriculum and jumping in and teaching it with me.

Optics (PHYS 323 here)

The labs in our department (and dare I say colleges everywhere), tend to be rather like “cook-books.” We put students in front of a equipment (a good thing), but then give them step-by-step instructions like “turn the voltage to 10, then write down the ion current” (a bad thing). Afterward, we tell the students what their data should look like, and even (exactly) how to analyze it. We don’t give the students much room to think on their own. To this end, a nice paper came out about giving labs where you remove the procedure from a typical lab, thus letting the students debate and assess what needs to be done to achieve a particular (measurement) goal given some equipment.

So, in the Winter of 2015, I did this for our optics labs (that is, removed the procedure from the labs). I kept the labs to just two pages, with no procedure, and a clear grading rubric for each. Here are my revised labs.

Notes:

  1. For some of the labs, I let the students take a break from writing formal lab reports, allowing them to draw “howtoons” of their results instead. Here’s what I got for the polarimetry lab: click.
  2. Although removing the procedure and allowing the students to think sounds like a good idea, it wasn’t. The students appear to love being told exactly what to do (a la the “cookbook” mode), and would spend most of the lab period desperately searching the web for instructions. One student even found a cookbook lab at another university and raised his hand to ask me “can I just do this instead?” Oh well.

Introduction to the Solar System (ASTR 101 here)

I started teaching ASTR101 a couple of years ago. It is a very fun class to teach (except when the students got mad at me for planning an exam on the day before Halloween, which prevented them from being able to “get ready for Halloween”). Here are a few “hands-on” activities I assigned, in order to get the students out and “looking up” at the sky.

Research

Research stuff

Publications

I had a few really cool publications recently:

Electric Car

Using an hour here and hour there during summer 2009-summer 2010, I converted my old 1992 VW GTI to a 100% electric vehicle. Here was the first step back in August 2009, taking out the dirty old engine.

I sold the engine to a scrap yard for $13.50. First the DC electric motor came in the mail (WARP Impulse 9),

which I mated to the transmission using a custom adapter kit from ElectroAutomotive (which I would not recommend doing ANY business with).

I then put this assembly back into the car, onto the original motor mounts. For additional support on the motor side, I hand-crafted some unistrut bracketing, which among other things for the car, I ordered from my favorite company, McMaster-Carr. The car is a front wheel drive, so the motor/tranny go in sideways, and connect to two half-axles which turn the two front wheels. Electric cars are quite simple in operation. An electric motor turns the gears in the transmission just like the original gasoline motor did. Check out this video, where I spun up the car using just a single 12V battery.

Update Aug 2015

To 2013 or so, I drove the car about 8,000 miles before the lead-acid batteries gave out. They would charge fully, but then be completely depleted after driving down the street and back. So the car sat in my garage for about 2 years or so, until I decided to take the plunge and buy some Lithium-ion ($$$) batteries. I bought 8-Enerdels, at 14.4 each (32 cells, with a max voltage of 3.9 volts), so the car is now 125V when all charged up. Here are some pictures...4 batteries in the front:

And four in the back:

I built a cool battery box too:

My "fuel gauge" is a voltmeter, 125V=full, 90V=empty:

I notice that the pack voltage goes down by 1 Volt per every mile that a drive, so I have about a 35 mile range, which is perfect for living in a small town like SLO. The batteries require a BMS (battery management system), which is basically an on-board computer that watches over the batteries during the charging and discharging (i.e. driving) process. The cells must stay between 3.9 and 2.8 Volts to avoid damaging them. But this require a huge rats-nest of wires, to the tune of 5 signal wires per battery, hence this mess:

That's the BMS unit in the middle right (with the heat-sink fins). That black cable in the foreground is connected to the accelerator pedal and the silvery thing to the left is my potentiometer (or "pot box") that controls the speed of the car. It all works fine and the car is a joy to drive. I like being able to monitor all batteries using a laptop connected to the BMS. The batteries are about 1/2 the weight (45 lbs each, not 75 like the lead acid) and about 2x the energy density. Although the experience of building the lead-acid version of the car was good for learning, I really can't stand those types of batteries. They are heavy, stinky (due to their battery chemistry), and corroded everything around them. I would not recommend building a lead-acid electric car.

Here’s one of my favorite pics of the car, it being “fueled up” in my driveway. Note how the suspension is still nicely balanced, versus that with the lead-acid batteries (below).

Longitude

So what's this longitude thing all about? For starters, read my paper about it (see ASTR 324 above) or the book I have been writing (see ASTR 324 above). Like everyone else, I read Sobel's book on "Longitude" back in the early 1990s. I had the opportunity to teach a class in London during the Summer of 2008, and I thought a course that examined the science behind the longitude problem would be a great fit. It was, and I have since turned the class into an general education class here at Cal Poly (ASTR 324) and taught it again a few times in London during the summers.

The whole story is just awesome, and has been a big part of my professional work. I've published two papers on it, a self-published book, and even got in to amateur horology. As a true "longitude disciple," I found Sir Cloudisley Shovell's Memorial here, and even posed the way the poor guy was likely found:

The "longitude problem" sort of works like this. Suppose you were a ship's navigator in the 1700s. You were far from land and looked out. This is what you saw in all directions, for two months at a time:

The question is then, "where are you?" The sea is pretty featureless for landmarks to navigate by. So what do you do? Back in the 1700s, lives were being lost and ships were being crashed. Did you know an average galleon back in the day took 10,000 oak trees to build (100 acres of trees)?

Latitude (N/S location) is straightforward to find using the sun at noon, or (if in the northern hemisphere), Polaris at night. Longitude (your E/W position), however, was not possible to find using the sky. Why? Well, in short any configuration of the sky can be produced by viewing it at a given longitude at a given time. Thus, your view of the sky is an inseparable mixture your time of day and your E/W position. If you want to use the sky for longitude, you'll need some absolute reference to disambiguate the two. So basically yes, in the mid-to-late 1700s, everyone was sailing half blind.

Sticking to strictly E/W ocean crossings was a popular technique (that is, sail and keep Polaris at the same height in the sky). You have to remember that back then there was no electricty, GPS, gasoline, radar, or even reliable maps. As soon as you lost sight of land, you may as well be on a different planet. Ships were powered by the wind and made of wood and tar. One would be very isolated out there on a ship. Yes, yes, on it goes. Here is an excerpt from my paper:

By the 1700s it was unfortunate that far-reaching expeditions were at great risk because there was no practical method of accurately determining one's navigational longitude. There are records of fateful expeditions both at land and sea5 due to this “longitude problem.” Conditions at sea made this problem particularly serious, and many lives,6 property, and political prowess were lost. The longitude problem is well covered in both erudite and popular treatments.

It was established that the simultaneous knowledge of one's remote (or “local”) time and that at a fixed reference point16 would allow for the determination of the relative longitude. Knowing (or keeping) the time at the distant reference point (from afar) was the most problematic issue despite three known methods for doing so. The first involved using the motion of the Moon, the second involved keeping time with a portable chronometer, and the third used observations of the motion of Jupiter's moons. These were all sound solutions17 that lacked a practical implementation. Harsh conditions at sea where accurate navigation was the most critical posed the greatest challenges to a longitude solution. Observing Jupiter's moons at sea was impractical due to the difficulty in tracking them from a rocking ship. John Harrison spent a lifetime pursuing the chronometer approach, while a succession of astronomers employed at the Royal Greenwich Observatory pursued the lunar approach.

The interested parties were all competing for the substantial “longitude prize” offered by the British government in 1714. The chronometer approach eventually won, although the techniques using the Moon and Jupiter (on land) all became usable by the late 1700s. The accuracy and ease of use of the marine chronometer caused it to become the dominant longitude-determining tool until worldwide time broadcasts in the early 1900s. The solution to finding longitude took the most convenient leap in the early 1990s, with the availability of the Global Positioning System (GPS). The longitude problem was an outstanding worldwide problem in the 1700s and was eventually solved using principles from physics and astronomy. We find it an appropriate topic for a college-level course for nonscience majors for the following reasons.

A course whose topics include the longitude problem, celestial navigation, and timekeeping is an original offering of general interest to students. The longitude problem provides a framework for discussing a variety of scientific topics in support of understanding this problem (and its solution) from a historical and contemporary perspective.

The longitude saga also presents an opportunity to demonstrate how science has worked successfully because it contains many of the essential elements seen in current scientific struggles, including a lag between a theory and experiment, pleas for funding, competition from other groups, originality, politics, experimental verification, dedication, and eventual triumph. Initial course planning can be guided with the help of books by Sobel, Sobel and Andrewes, and Dash, which provide concise and popular adaptations of the longitude problem. These books lack the scientific details needed for this course, which are amply supplied by Andrewes. A study of just the longitude problem alone will generally not fill a course consisting of approximately 40 lectures. The longitude problem has two very natural branches, one into celestial navigation and the other into the science of timekeeping.

The course itself is also full of basic astronomy and physics; it is quite fun to teach and lots of demonstrations from a physics department demo-room can be used.

Graphics

In recent years, I've embraced the idea of using computer graphics in freshman physics. Here's a book I published about it all.

Unfortunately, I do not use this method at Cal Poly at the moment. Although I think this computation/animation method is single handedly the best way to teach and inject life into poor old introductory mechanics classes, adapting it to a given student body is rather tricky. Students at Cal Poly, for example, seem to rather want to stick to paper and book physics. It is something I need to spend more time working out before doing this again. If you want to look, the website that drives the whole this is Physgl.org.

Cover

A paper I wrote with M. Moelter made the cover of the American Journal of Physics for March 2013. Wow!

SCM-302: Learn by Doing Lab (LBDL)

Spring 2018: Students needed!
Sign up for Bensky's Fri 9am-12pm SCM-302 lab.
Teach electronics to 5th graders using PLAYDOH!

The Story...

​As part of Cal Poly's CESAME program, we developed a "physics learn-by-doing lab" that we started running in the Spring of 2012. The target audience for the lab is 3rd - 5th graders. It involves building electronic circuits using Play-Doh.

Why Play-Doh? A while back, I saw a Ted talk on "Squishy Circuits," which uses conductive properties of Playdoh (yes Playdoh) as a platform for building simple circuits.

Playdoh itself seems like a perfect "in" for this age group, so it seemed like a good idea for this project. So, using my favorite electronics retailer (Allelectronics.com), we stocked up on every interesting electronics component I could find (potentiometers, LEDs, switches, motors, buzzers, etc.). With this, 10 kits were made, which can be handed out to the kids when they visit. Here are a few pictures. (This entire effort has been published here.)

You (blue coat) and the kids (white coats)


Winter 2019: LS-305
Project Based Learning in STEM Education

3D printing, Arduino, Coding and Robotics

Course Details

What is this stuff?

Coding

Coding is where software comes from, and software is what tells a computer what to do. In this class, you'll learn how to instruct the computer to do just what you need it to do. We'll focus on the Scratch programming language, where you code by connecting blocks like a puzzle, like this:

You'll learn all about coding in Scratch, by making fun graphical-based programs---all by connecting blocks!

3D printing

Imagine thinking of an object, and within minutes, holding it in your hand! This is what 3D printing is all about. It is where design enters STEM. 3D printers make objects you design out of layers of plastic. Here is an Eiffel Tower being printed:

3D printing is the ultimate in the maker/creative process, allowing a hypothetical design to become a real object. Imagine having a future class of yours make their own fidget spinners?!? Or science project parts?

In this class, you'll learn to design an object using TinkerCAD, and see how to prepare it for printing on a 3D printer. (You'll actually print your design on a real 3D printer too!)

Robotics

Robotics is the ultimate in taking coding into the physical world. Here, you'll use your Scratch coding skills to command a robot (here the Finch robot) to roll around the room!

You can use code to change the color of its light, to roll forward, or turn when it hits an obstacle.

Arduino

You can hardly even think about the maker-movement without hearing the word 'Arduino.' Here it is:

What is it? The Arduino is a $20 computer with no keyboard or screen. So what good is it? Plenty! The black rows (with the small holes) are connectors, that wires can be pushed into. The wires can be connected to lights, motors, sensors, etc. So the Arduino can be made to interact and moderate electrical devices it is connected to (and buried inside of some cool invention). In this class, we'll even use the Arduino to acquire (then plot) scientific data!

Makers have embraced the Arduino as "brains" for their inventions: controlling drones, robots, cat feeders, or halloween costumes. Here is TED-talk about it:

Need more proof? Look here.