FredBot: FRee EDucational RoBOTics Platform

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FredBot; the Free Education Robot

Tabor Henderson

Lab Assistant

Department of Physics Metropolitan State University of Denver

July 23, 2013

Abstract

This paper describes an open-source hardware platform (FredBot) in-

tended as a candidate replacement for the blackbox-style lab platforms

provided by Pasco and other educational lab equipment manufacturers.

We discuss the educational opportunities provided by open-source hard-

ware, as well as the expected difficulties. We begin with our motivations,

then replicate a Pasco data set with FredBot, and compare the two sets.

From this comparison, we develop our ideas for next steps. We con-

clude that open source hardware provides remarkably complete data and

a holistic learning experience, but requires thorough development before

deployment.

1 Motivation

The undergraduate physics lab currently uses Pasco products for almost all of

our equipment needs, including physical items like kinetics tracks and carts,

and electronic components, like the 750-series interface box and sensors. While

generally well-made, the Pasco equipment is very expensive. The 750-series

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boxes cost over $700, and have already been replaced by the 950-series, which

costs $900. These devices mediate between the lab computers and sensors,

and this is where I first realized how easily they could be replaced. This is

also the biggest flaw in Pascos products; they all rely on the interface box,

forcing experiments to rely on real-time communication between the desktop and

sensors. Our biggest problem with the Pasco equipment has been the interface

boxes, almost always with their USB firmware. FredBot avoids this issue entirely

by design, but it comes with a loss in educational experience. FredBot trades the

ability to view real time data for a transparent, open platform. Pascos approach

is a blackbox style design, in which the students dont need information on

the nature of their data-collection apparatus. With this design, students dont

need to understand that their motion sensor is actually a position sensor, only

that it provides data up to a certain accuracy. 1

With FredBot, we pursue three design elements: reliability, clarity, and cost.

FredBot is essentially bulletproof by way of modularity. If any component

fails, it is replaceable for less than $30. FredBot also functions completely

transparently; it relies on less than 40 lines of code, and all functions are explicit.

There is no motion sensor with FredBot; only a position sensor, a datalog,

and the students ability to manipulate that data. Finally, the current version of

FredBot costs less than $100 plus assembly time, and could provide serviceable

data in most of our kinetics labs.

2 Description of Materials

The Arduino open source prototyping platform is the core of FredBot. It in-

cludes a development environment with many libraries. In fact, we did not

1As a student, the author personally benefited from this. Watching the real-time graph

of kinetic vs. potential energy was fascinating, and a powerful learning experience. This

advantages are lost with FredBot, but may be recoverable with additional development.

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write more than 10 lines of code for the main program; it simply consists of

two pieces of integrated library code. A major feature of the Arduino platform

is its shield system. This allows major components to be dropped in and

expanded further by the user. Available shields include our memory module

listed above, various types of wireless communication, touchscreens, high volt-

age controllers, sensor relays, and more. Additionally, shields always leave at

least some of the mainboards pins open for other sensors. We utilize both fea-

tures in FredBot.

FredBot itself is simply the components above assembled in the enclosure. It

is sufficiently compact to be mounted securely to the Pasco kinetics carts with

velcro straps. The Ping))) sensor needs a fairly large target. We mounted Fred-

Bot to the cart, allowing the target (10.012.5cm cardboard sheet) to remain

stationary. This provided initial data, but it was not easily comparable to Pasco

data. So, we collected data using both systems in a consistent way, described

below.

Description Cost

Arduino Uno Rev 3 open source prototyping board $25

Seeed Studio SD/mSD shield $10

Parallax Inc. Ping))) Ultrasonic distance sensor $30

Radioshack Enclosure Project Skeleton Kit $25

battery pack & miscellaneous connectors $5

total $95

3 Data Collection Procedure

To compare the two data collection systems, we collected position data from the

end of a kinetics cart, with the ultrasonic senors pointing at the cart in both

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cases. We collected data on a kinetics cart standing still, as it fell down an

inclined track, and after an impulse away from the sensor. Due to differences

between the systems, we collected all of the Pasco data, then all of the FredBot

data. FredBot required reprogramming between each run, which significantly

slowed progress.

With the Pasco equipment, we collected data on three runs of each type

listed above at 10Hz, 20Hz, and 50Hz resolutions, for a total of nine data sets.

This frequencies result in a delay between data points of 0.1s, 0.05s, and 0.02s,

respectively. With FredBot, the Ping))) sensor triggers after a five microsecond

signal high, releasing a sound pulse, then returns the signal high when the

pulse echo hits the sensor. Then, the program converts the time difference into a

position and delays. We ran with the delay at 100ms, 50ms, 25ms, and 10ms to

approximate 10Hz, 20Hz, 50Hz and 100Hz cycle times. This resulted in twelve

data sets.

4 Analysis

Presented are the charts generated from the data runs. The raw position data

has a few anomalies in the FredBot runs, in particular in the impulse runs, and

in one fall run. These are probably due to the experimenters clumsiness, as

they all occur as the cart is released. Also note that the data on the stationary

cart is somewhat deceiving; all three of the Pasco runs occured with the cart

at the same spot, the four FredBot runs occured with the cart in four distinct

positions.

Despite the anomalies, FredBot succeeded in providing data at a higher reso-

lution than the Pasco sensor. We believe this ability is worth developing further,

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and integrating into pedagogical design. 2

5 Next steps

There are many possibilities for integrating open source designs in the class-

room. FredBot, as it stands, provides one such possibility, but it could be much

improved. We could try to develop FredBot into a drop-in replacement for prod-

ucts like Pascos interface boxes. However, this requires development of a signal

generator, additional sensors, and a more robust software package. Also, trying

for a Pasco workalike probably misses the purpose of open source. Pascos

products are effective in the classroom because they facilitate a particular learn-

ing style, that which tolerates suspension of disbelief and abstractions. When

one can delve completely into the context of physics, its hard to beat their plat-

form. But some students, inevitably, find the equipment itself more interesting

than the content its supposed to teach. Arduino, being an open platform, in-

vites a different, more experiential learning style. Those students distracted

from physics by gadgets will hopefully find their perspectives enhanced by see-

ing exactly how their experiment works.

Besides Arduino, other open source platforms are available. Arduino has

a thriving user community which shows no sign of slowing down in the near

future. The Arduino platform is used by hackers worldwide in everything from

quadcopters to automatic gardens. I believe it to be as permanent as Pasco.

However, any open platform provides the same basic benefits, and most can

make use of the same sensor systems.

We believe the most useful immediate next step would be exploring alterna-

2The analysis given here is rudimentary, and comes with the note that we would gladly

work more with the data, given some advice on how to make it useful.

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tive sensors in the same or similar lab experiments. For example, accelerometers,

commonly deployed in mobile devices have grown highly accurate and robust.

These sensors could provide cleaner data, less susceptible to environmentally

introduced errors. Alternately, we could focus on developing the ultrasonic sys-

tem to the standard required currently. As a third possibility, we could pursue

alternate open source platforms. Finally, rather than continue developing spe-

cific lab components, we could begin equipping the Society of Physics Students

chapter with the necessary equipment for developing lab experiments. Experi-

ment development could earn the student money, class credit, or fulfill an honors

requirement. In summary, our next steps could include:

1. Development using alternate sensors

2. Further development using ultrasonic sensor

3. Development using alternate platforms

4. Organizational development

We seek recommendations and advice. Please email any and all thoughts to

tabor.hendersongmail.com.

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Documents

FredBot: FRee EDucational RoBOTics Platform