Andrew Burks

Tag: Design

Finalized Vibratron Design

by on Jan.29, 2011, under RobOrchestra, Robotics Club, Vibratron

After a successful design review at the weekly Wednesday meetings, the final modifications were made to the Vibratron design.  After only a few major changes, the completed Vibraphone design looks something like this:

Full Iso

Instead of relying on tension in cables or cloth to keep the wings in their proper place, kickstands were added to each wing to keep it in the right position.  The kickstands also serve as the mounts for the cables that will be keeping the cloth tensioned.

Structure with Wires

All surface that could potentially come into contact with the steel balls are covered in a 1/8” thick layer of neoprene foam.  The foam will be attached with an adhesive instead of using hardware.  The longest diagonal of the final outer area of the robot are just under 8 feet.  Despite a few minor edits in the basin, the addition of the kickstands, and some other tweaks, Vibratron is still able to fold up into a neat 1’x1’x4.5’ column for storage and transport (excluding the two separate racks of key units).

From Below - Contracted

The entire structure is made out of 94 feet of aluminum 1”x1” angle, varying in thickness from 1/16” to 1/4”.  That aluminum has been ordered ($140.61) and fabrication of the main structure should be underway before mid-February.

With only $200 left in the $1,000 budget, the group still needs a 48’x36”x1/4” sheet of aluminum to waterjet into some very important pieces.  Using cheap 3003 H-14 aluminum sheet, it will cost $160 just for the raw materials for those pieces.  That leaves only $40 in the budget for fabric, foam, a power supply, steel cables, and other hardware.  Obviously the ends won’t be meeting, so we need to look for a donation of the aluminum plate.

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Vibratron: Fitting Through Doors

by on Jan.19, 2011, under RobOrchestra, Robotics Club, Vibratron

Something I never considered when designing previous versions of Vibratron was its ability to fit through doors.  While the old design could fit through a set of double doors, we wanted the entire robot to be able to fit through a standard door.  This change in criteria required some major changes in the design of a few parts of the Vibraphone.  It also allowed for a few other system upgrades in the process.  Keep in mind that all of the renders here do not include any foam/cloth skin that will be used to contain the balls.

Full Model No Skin - Iso

Giant Circle Full of Key Units

The large waterjet circle that held up all of the key units was three feet in diameter.  Combined with the overhang of some of the key units, the diameter of the robot was at nearly five feet.  Separating the giant circle into two large semicircles fixes the problem pretty easily.  Hand grips were added so that the semicircles could be carried easily.  Even though they are 25 pounds each, the semicircles can be carried close to the body with arms locked, which is a requirement for simple transportation of the machine.

Giant SemiCircle

Full Model No Skin - Topish

Fold Out Wings

Instead of the large fixed upside-down-umbrella style from the previous design, this design has four fold out “wings” that catch the balls and funnel them towards the center.  The overall diameter is six feet when open, but the wings can fold up completely vertically alongside the column.  Between each wing is a pie-wedge shaped piece of cloth or foam.  This has a duel purpose of funneling balls toward the center and regulating the deployment height of the wings.  When the wings are raised, the compliance of the cloth/foam will allow it to fold.

Full Model No Skin Collaped - Iso

Deeper Square Basin

The previous basin was a thin circle, but our research with the prototype of the recirculation system has suggested that we will need many more balls in the system to reach steady state.  A wide square basin rigidly integrated with the vertical columns can hold the necessary volume of balls.  Four trapezoidal sheets of plastic also keep the balls rolling towards the center of the basin.

Basin Closeup

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Improved Key Unit

by on Dec.11, 2010, under RobOrchestra, Robotics Club, Vibratron

After several attempts at getting the 180 separate parts necessary for the previous vibratron key unit laser-cut, we finally found a feasible method for fabrication.  The father of a roboclub member offered to us the use of his large CNC routing table.  Because Acrylic does not machine well (it is much too brittle) some redesign was done to make the key units out of hardboard.

Design Changes

Hardboard - Key Unit

The biggest change between designs was the decision to not remove the material between key points, exchanging concave cutouts for straight lines.  Each new unit is made of five separate pieces of hardboard, connected by wood glue (instead of plastic welding).  Only two parts per unit are unique, instead of 3, which makes machining prep and assembly easier.

Circular Structure with New Key Units

Hardboard - Full Circle

The new key units attach to a horizontal 1/4” plate, just like the previous version.  The only difference is that instead of two clips and two colder pins, these units attach with just a colder pin.  Nothing else in the structure needed to be modified to accommodate the change.

Machining

All of the pieces for all 30 key units can fit on five sheets of 2’x4’ hardboard.  Hopefully these items will all be machined by the end of the winter break so focus can be shifted to the design and fabrication of the structure instead.  Below is an example of how the pieces fit on a sheet of hardboard.  The labels are engraved .02” into the board, and everything else is a profiling cut.

Cut Sheet 1

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Robotic Manipulation Cup Stacking

by on Dec.02, 2010, under Classwork

Challenge

For the final lab assignment in my Robotic Manipulation class, we were challenged to competitively stack cups.  We were given six 3 inch tall plastic cups, and were instructed to make a 3-2-1 pyramid out of them, then destroy the pyramid, as quickly as possible.  Before we even began working on the project the best team had already done it in only 12 seconds.

The robot arm is currently equipped with a descent pneumatic gripper.  Two big plastic pads squeeze the cups one at a time to contain them.  Stacking cups one at a time is inefficient, but teams were doing it.  Nico and I decided that we needed a some mechanical advantage.

Denso End Effector

Design Goals

The biggest design limitation was that the only way to actuate our device would be to integrate with the existing gripper.  This limits us to on-off control, which prevents us from picking up all of the cups at once and releasing them strategically.

However, the bottom stack doesn’t really need to be picked up, it only needs to be slid across the tabletop.  Also, picking up two cups at once for the middle layer saves time as well.  The top cup could even be optimized by dragging it into the stacking area initially.  If any of these goals could be met, it would give us an advantage over the other teams.

Interface

In our previous lab, we were able to use the gripper to attach our end effector to the DENSO arm.  However, because we rely on the actuation of the gripper to activate our mechanism, we needed an alternate means of attachment.  The T-slots on the end of the DENSO arm are the perfect size for a 1/4” nut, which is the standard size for a #4 bolt.  Attaching here gave us a reliable fixed reference point.

Combined

Fabrication

Using the robotics club CNC, I was able to build the 6 parts necessary for the device.  The only problem I encountered was bowing and vibration in the middle of the largest piece.  Because my piece (11.58”x3.68”) was near the maximum limits of the machine (12”x4”), it was difficult to secure the middle of the stock.  All in all, it took about 5 hours of machining to build the entire mechanism, half of which was slow-going CNC time on the largest piece.

Gripper

Performance

In the end, we were able to achieve a time of 5 seconds.  Nico and I are pleased with the results, and expect to have the fastest time in the class.

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Tactile Simon

by on Nov.18, 2010, under Personal Projects, Simon

Years ago, when I was in elementary school, my cousins Lisa and Erin would always give my brother and I great Christmas gifts when the extended family got together for Thanksgiving.  Now that they both have kids of their own, I thought it was about time to repay them.  Two weeks before Thanksgiving this year, I got the idea to use my robotics experience to make a toy for each of the families.

Idea

I wanted a toy that was interactive, but simple.  I needed moving parts, but nothing fragile or exposed.  Somehow I came up with the idea to do a tactile version of Simon.  All I knew was that I wanted a wheel you could grip that would spin in a pattern that you had to repeat.  The toy needed to be entirely encased to protect the electronics, but I wanted the kids to be able to see what was going on inside as well.

Full Iso

Design

Mechanism

On top there is a wheel with four colors on it and notches around the outside for gripping.  The top wheel is made of clear polycarbonate and the colors are printed on transparency paper and attached with contact paper.  This design lets the LED in the notch below one section of the wheel illuminate the active color by shining through the colored transparency.

There is a second wheel below the top cover, but it is constrained to rotate with the top wheel.  It is made of white HDPE, with strategic portions of its bottom surface colored black.  Both of these circles are attached to a Servo which can rotate the wheels in either direction at variable speeds.

Mechanism

Interface

The primary sensors on this robot are the four IR emitter/detector pairs.  A combination of an infrared LED and phototransistor, these sensors allow a microcontroller to determine how reflective a surface is.  Because white surfaces are more reflective than black surfaces, this sensor pair can parse the pattern of black and white on the bottom wheel.  Combined, these sensors tell the robot how the wheel is oriented.

Besides the power switch, the only other input device on the robot is the button on the left of the device.  After turning the wheel to a certain color, pressing this button will log the current color as your next guess at the pattern.

There are two LEDs on the robot.  One is in a cutout below the top wheel, and it is used to indicate the currently active color.  The second LED is an RGB LED, so it it capable of producing different colors on its own.  Displaying Red, Yellow, Green, or White during different portions of the game provides great visual feedback for the user.

Finally, there is a buzzer which allows the toy to make noises all across the audible range of human hearing.

Bottom

Electronics

Everything plugs back in to an Arduino Duemilanove, which does all of the thinking.  Most of the components only need to be plugged into the Arduino to be ready to go, but some of them need to go across a resistor or capacitor first.  The IR emitter/detectors, however, are a bit of a pain.  I had to make a board that slips female headers right over the sensors’ leads and routes them through all the proper resistors to finally output a sensible signal to the Arduino.

The servo requires some special electronic attention.  Because I want people to be able to backdrive the Servo, I need to completely disconnect it from its power supply when it is the human’s turn to spin the wheel.  Using a custom MOSFET board designed by my friend Nico Paris for our RobOrchestra project, I was able to selectively power the Servo.

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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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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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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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