Andrew Burks

Archive for October, 2010

Robotic Manipulation Clock Lab: Working!

by on Oct.26, 2010, under Classwork

After a total of around 4 hours on the robot, Nico and I got the arm to work!  We have two modes: one that displays the current time, and one that will count off time from a predefined starting point.  Here are some videos of us testing at about 1:10AM on Sunday night.

I had to modify the pen and eraser holder a little bit to make it work.  I needed to make the drip area fatter, because the fingers don’t actually close all the way.  Also, I needed to mount the pen and eraser at a really close angle, because it took two seconds to rotate the tool by 90 degrees, which was unacceptable.  By adding a fancy part to the original assembly, I was able to make it all work.

Tool Render - Modified

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Robotic Manipulation Clock Lab

by on Oct.20, 2010, under Classwork

The second lab in my robotic manipulation class involves telling time with the 6-axis denso robot arms.  My lab partner Nico Paris and I decided we wanted to tell time by drawing lines on a white board and erasing them.

Instead of drawing numbers, we are drawing 9 equally spaced lines radially out from a point.  No line translates to “0” and some number of lines corresponds to that digit.  There are 6 of these sets of lines, corresponding to two hours digits, two minutes digits, and two seconds digits.

In order to draw and erase lines, I got to make a cool tool for the robot to hold.  By rotating its last joint by 90 degrees the robot can switch between the pen and eraser.  What’s even cooler is the spring built in to the pen part of the assembly to allow for some compliance without totally squishing the pen!

Here is a render of the tool, and a cross section to demonstrate the compliance in the pen.  Photos and video of the final product in action are forthcoming.  We demo the design on October 18th.

Tool Render

Pen Assembly Cross Section

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Vibratron Ball Collection Structure

by on Oct.19, 2010, under RobOrchestra, Robotics Club, Vibratron

Design

After bouncing off of the vibraphone keys, the ball bearings need a soft place to land and a central basin to roll into.  The basic idea behind the design was to make an upside-down umbrella, with the skeleton on the outside.  Stretching 1/4” foam between sections of aluminum angle is a cheap way to cover a lot of area.

Ball collector

Structure

Ball collector basin skeleton

Structure - Basin Detail

Incorporation into Full Model

While previous renders imagined the 180 pieces of acrylic supporting the keys to be red, clear acrylic being about 35% cheaper prompted a slight design change.  We should save about $100 by changing to 1/8” clear acrylic.

The full vibraphone is now 4.5 feet in diameter, and should be about 3.5 feet tall.  The rim of the basin is just 2 feet off the ground, which is good because want people to be able to look into the vibraphone.

Full Vibraphone (without recirculation screw and ball distribution)

Gates and Foam - Overall

Detail view of key unit/basin interaction

Gates and Foam - Detail

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Vibratron Structure

by on Oct.12, 2010, under RobOrchestra, Robotics Club, Vibratron

While I had made some preliminary designs of the Vibratron structure a few months ago, I can now begin to finalize some of the key support structure as the ball dispensing mechanism is finalized. 

Key Unit

Experimentation showed us that the ideal location of the ball dispenser is with the tube perfectly vertical, six inches above the center of a key tilted at 45 degrees.  A modular unit consisting of 4 pieces of lasercut plastic and a gate mechanism was designed to hold the keys and gates in their proper relative positions.

Key Unit - Alone Iso

Key Unit Mounting

A large sheet of 1/4” thick aluminum will be waterjet into a shape that can hold 30 of these key units.  Each unit will be attached to the aluminum by two lasercut clips which are held down by cotter pins.

Circle with single Gate - Front Iso

Circle with single Gate - Back Iso

30 Key Units

With 30 key units on one large piece of aluminum, the weight of the entire assembly is already at 50 pounds with a diameter of over 3 feet.  In the future, the ball recirculation system (an Archimedes screw leading into a paintball hopper) will rise out from the middle of the aluminum circle, and the ball collection system (a foam floor to catch the balls) will stick out below and around the keys.

Circle with Gates - Overall

Circle with Gates - Detail - Front Depth

Circle with Gates - Detail - Back

180 pieces of plastic, over 90 of them unique

There are 6 pieces of lasercut 1/8” red acrylic in each of the 30 key units.  3 of those 6 pieces are unique.  1 of the other 3 pieces has 6 different sizes, and the final 2 are each repeated in all 30 assemblies.

Obviously I did not want to model 98 different pieces of plastic and insert them individually into models.  Fortunately, design tables in SolidWorks are very powerful.  In the end, I only needed to make 5 plastic parts and 5 obnoxious Excel spreadsheets to get an assembly (“Key Unit”) with 30 unique configurations.  Some of the plastic parts even have their note engraved into the side!

Design Table

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HarmonicaBot Begins

by on Oct.11, 2010, under HarmonicaBot, RobOrchestra, Robotics Club

The Carnegie Mellon Robotics Club has announced $500 in funding for HarmonicaBot!  This is good news, because there was no where else for funding to come from.  The one caveat is that I need to have a proof of concept in order to unlock the final $300 of funding.

During the presentation, some other interesting means of funding were mentioned.  It was recommended that I speak to Clippard directly to try and obtain my 12 solenoid valves for free or at a reduced price.  Also, an engineering professor at CMU who is very involved with harmonicas might be interested in doing something with this project.

Plug

In the hour before the funding presentation, I modeled and rendered a crude first iteration of the plug.  This version routes a 1×10 array of square holes on the harmonica to a 2×5 array of 1/8” NPT fittings on the back.  The harmonica sticks inside a bit, where two pieces of foam or rubber apply pressure to keep the harmonica up against the plug.

Harmonica in Plug

The next image is a cross-section of the plug.  The curved parts of the channel may seem to end before reaching the harmonica on the left, but they don’t.  Instead, one of them crosses out of plane towards you, and the other crosses out of plane into the screen.  This complex geometry is why the part needs to be 3D-printed or cast.

Plug Cross Section

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HarmonicaBot

by on Oct.08, 2010, under HarmonicaBot, RobOrchestra, Robotics Club

Autonomous Harmonica-Playing Robot

I have wanted to add a diatonic harmonica to the RobOrchestra since I joined the group in my freshmen year.  The Carnegie Mellon Robotics Club recently acquired a MakerBot 3D printer, so my dream has become a lot more feasible than before.

Harmonica - Hohner Special 20

Harmonica Interface and Control

The concept for the robot is simple: A 3D printed plug (with complex inner geometry) routes the 10 square holes of a diatonic harmonica to 10 NPT fittings.  The NPT fittings connect to 10 different solenoid valves, each corresponding to one hole on the harmonica.  This allows for individual control of the air going through each hole.

Achieving both “Blow” and “Draw” Notes

The solenoid valves all connect to a single manifold, which is connected to two other solenoid valves.  One of the two valves is connected to positive pressure, and the other is connected to negative pressure (vacuum).  Activating one of the two solenoid valves at a time can simulate a blowing or drawing, while the other 10 valves select any number of holes on the harmonica to play.  Unfortunately, like humans, this robot will not be able to blow in some holes while drawing from others.

Manifold - Iso

Harmonicas of Different Keys

The best part about having one generic plug to route the 10 holes to 10 NPT fittings is the modularity it provides.  Diatonic harmonicas come in all sorts of keys, but they all have the same shape.  Because of this property, harmonicas of different keys can be easily switched in and out of the mechanism.

Funding

The estimated cost of this robot is at $500.  This project is applying for RoboClub project funding, but will not be applying for a SURG.  The largest cost is the 12 solenoid valves at $20 each.  More updates and design will follow if the project gets funding from somewhere.

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Vibratron

by on Oct.04, 2010, under RobOrchestra, Robotics Club, Vibratron

Also from my update of the RobOrchestra website.  I apologize for the redundancy.

Description

Vibratron is one of the main RobOrchestra projects for the 2010-2011 year. After receiving $1000 in grant money from the Undergraduate Research Office in the form of a SURG and a donated vibraphone from a former member, the team began designing a robotic Vibraphone.

The overall vision for the project involves laying out the 30 vibraphone keys in a circular array and dropping steel ball bearings onto the keys in order to create music. While other more direct methods might have been more effective, the group opted to create a more unique piece of art.

The project is currently in the prototype stage, but the general layout has been designed. The robot will be composed of three main systems. One of the systems will dispense the balls onto the keys, one will collect the used balls and recycle them to be used again on a different note, and the third system will be the structure of the robot that hold the keys and all other systems together.

Mechanisms

The ball dispensing mechanism has been through two complete designs. The initial design used a rotating notched wheel attached to a stepper motor to dispense balls one at a time. The second design used a solenoid as a gate to block and release balls from a queue. Both designs were prototyped, and the solenoid design was chosen because of its greater speed and reliability over the wheel design. Each of the 30 gate mechanisms will cost less than $5.00, and will be capable of dispensing over 14 balls per second. There are renders and photographs of the gate below.

The recirculation mechanism is basically an Archimedes Screw that brings balls from a lower hopper to an upper hopper. Once in the upper hopper, a paintball-style system will be used to spread the ball bearings into the 30 individual tubes, each of which routes to a separate gate.

The structure of the system will not be designed in any detail until the kinks have been worked out of the other two systems. However, a conceptual render of the desired circular layout of the Vibratron is below.

Logic

An Arduino Mega will be used to control the robot. A MIDI shield will allow the Arduino to read standard MIDI signals from any controller, and software will decode the MIDI commands into notes.

Each of the 30 gates will have a small custom printed circuit board (PCB) with a MOSFET and LED. This circuit board receives a digital signal from the Arduino and uses that signal to turn on the solenoid for a certain amount of time.

Images

Side view of the gate mechanism

Render of the gate mechanism

Final gate prototype

Conceptual render of the basic Vibratron layout

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Flutophone

by on Oct.04, 2010, under RobOrchestra, Robotics Club

Another post I made for the RobOrchestra Website:

Description

Flutophone is one of the oldest members of the RobOrchestra. It’s seven fingers cover and reveal the seven holes on top of the recorder in order to specify particular notes.

Currently Flutophone is in a semi-functioning state. The instrument itself has gone out of tune over time, but it cannot be replaced by any recorder except one with the exact same hole spacing because the fingers are not adjustable.

Mechanisms

Flutophone’s fingers were originally made of cheap hardboard. After considerable use, the keyway on the hardwood gave out and fingers began to slip. Recently, the fingers have been replaced with laser-cut acrylic and reattached to the original sprockets. The sprockets are turned by servos mounted within the casing.

The air flow is controlled by a solenoid valve. The input of the valve is connected to a compressor running at approximately 30psi. The output is connected to the mouthpiece of the recorder, with a latex balloon serving as a buffer to stifle the initial surge in pressure when the airflow is first activated.

Logic

The entire robot is controlled by a single Arduino Duemilanove. It takes in serial commands from a master controller and interprets them as notes with a duration. It then sends a PWM signal to each of the 7 servos to position each of the 7 fingers properly. After a short delay to allow for the fingers to reach their position, it activates the solenoid valve. When the robot is not playing a note, its resting state is with all holes covered.

Images

Note the Arduino in the top right and the Solenoid Valve in the bottom left

The balloon seals perfectly over the mouthpiece

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Final Gate Design Testing

by on Oct.04, 2010, under RobOrchestra, Robotics Club, Vibratron

The mechanism we designed on Wednesday was constructed this past weekend.  It takes about one hour to manufacture each of the three parts that comprise the gate mechanism.  However, it costs less than five dollars to construct a full gate assembly.

Fabrication

The assembly turned out just as planned.  The only issue that we ran into was that there needed to be a washer between the solenoid mounting plate and the tube in order to keep the solenoid and window lined up.  Each of the three parts will need to be machined 30 times to assemble the full Vibratron.

Tube

The extruded aluminum tube that the balls roll through has an inner diameter of 0.5” and an outer diameter of 1”.  In the final version it will be much shorter (roughly three inches long) but for testing purposes a longer tube was used here.

On one side of the tube there are a set of holes drilled and tapped for a #6-32 bolt, with a channel milled in between to allow clearance for the solenoid bracket.  Orthogonal to those features is a through hole for the tip to enter the tube and a counter-bore on that hole for an o-ring to sit in.

Mount

The mount connects the tube to the solenoid, and the assembly to the rest of the robot.  In this version, instead of an L-bracket like in the rendered design, we used a plate for simplicity.

Tip

Made from HDPE on a Lathe, the tip blocks the balls from passing through the tube when down.  The conical shape prevents the tip from jamming on the top of a ball when closing.  The flat end of the tip has a hole for the solenoid to mount in.  A perpendicular set of holes connects the tip to the solenoid with a #4-40 bolt.

Side View

Gate Prototype - Side

Detail View

Gate Prototype - detail

Testing

During Sunday’s meeting the team put the mechanism through a variety of tests.  The end result was the decision to move ahead with the design and incorporate it into the main Vibratron assembly.

Speed

Two potentiometers were used to vary the two delays involved with letting a single ball pass through the mechanism.  The first delay controls how long the solenoid is powered.  During this time, the gate rises up.  The second delay controls the minimum amount of time it takes for the spring to return the gate to a closed position after the solenoid is turned off.

After considerable testing, it was determined that the perfect amount of time for both parameters is 35ms.  This means that it takes 70ms to dispense each ball at maximum speed (obviously you could go slower, effectively increasing the second delay).  At this speed, the mechanism can dispense over 14 balls per second!

Power Draw

When left on for a significant amount of time (>1 second) the solenoids draw 3 amps at 12 volts.  This is a large amount of current.  However, when the solenoid is only on for 35 thousandths of a second, the average current draw drops to around .9 amps.  With a capacitor in the power circuit to soften initial power spikes when the solenoid is first turned on, the power requirements of the device seem much more reasonable.

Durability

The final test of the mechanism was to test its durability.  The device was run for 1000 consecutive cycles, mostly without any balls in the tube.  After the cycles completed, the solenoid was only slightly warm.  Because of the low (10%) duty cycle of the solenoid, overheating was a major concern.  But after this test, the group is confident that this solenoid can perform adequately.

In the initial prototype of the gate mechanism, the plastic tip was bent and mangled after only a few hours of testing.  In the new version, the o-ring support the load of the closing gate on the sides instead of the tip.  The durability test showed the the tip could maintain its shape even after significant use.

Video

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