Andrew Burks

Vibratron

Vibratron Auger Testing

by on Feb.25, 2011, under RobOrchestra, Robotics Club, Vibratron

The initial iteration of the auger was just installed into the nearly completed structure.  Mike made some pretty creative parts that will be assembled in the near future.

These clips hold the door brush to the side of the PVC sheel around the auger.  The brush is critical because without the resistance of the bristles, the balls would just roll down the auger.  The clip on the left is different because it needs to clear the motors on the agitation assembly.

DSC00891

These two waterjet parts were, as usual, provided by the generous Richie P.  The one on the left is where the 30 tubes of balls will plug into the agitation/distribution assembly.  The circle on the right is made of steel instead of aluminum.  It acts like a ring gear, and with rubber triangles along the perimeter, is driven to disrupt any balls that might be jammed at the entrance to one of the 30 holes.

DSC00898

This video highlights the first time we turned on the auger after it was mounted in the main structure.  Besides showing the coolness of the auger, it also shows all the progress we made on the structure!

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Continued Vibratron Construction

by on Feb.23, 2011, under RobOrchestra, Robotics Club, Vibratron

The main structure was assembled and is now able to support all of the keys, as well as a big bucket of balls.

The sloped basin which funnels the balls into the auger:

Basin with Trapezoids

Raised key units with some main structure:

Raised Circles

One of the wings:

Wing - Single no Foam

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Vibratron Structure Construction Underway

by on Feb.09, 2011, under RobOrchestra, Robotics Club, Vibratron

Metal Cut

After a bit of confusion with OnlineMetals.com, I got all 94 feet of Aluminum 1”x1” in the mail.  I cut it up into the appropriate lengths using the cool new carbide-tipped miter saw in the robotics club.  In the end, there are 54 lengths of angle that all need holes drilled in specific places.  All these pictures are from my cell phone, so bear with me…

40 of the 54 lengths needed for the vibraphone:

Cut Angle

Key Units Painted

The first attempt at painting the key units was a complete failure.  However, Megan Dority suggested that I used primer, and even picked some up for me.  It worked like a charm.  Also, Austin Buchan was able to get the group access to the Newel Simon paint booth, which was a huge help.

Key units drying in the paint booth:

Key Units - Paint Booth

Key units after drying:

Key Units - Cart

Waterjet Parts Donated

RobOrchestra founder and alumnus Rich Pantaleo came through once again for the group.  He was able to obtain a large donated sheet of 6063 Aluminum in just a few days when we needed it most.  Also, he cut out all the parts we needed just a few days after getting the sheet!  I made a few mistakes on those parts, but nothing too critical.  I had to widen half of the slots in the giant half circles because I didn’t account for the thickness of the paint and the oversized hardboard.

Completely assembled and painted key unit:

Key Unit - Single on Circle

Key Unit - Single on Circle (below)

All of the key units on their half circles:

Key Units - On Circle - Top Iso (Prelim)

Key Units - On Circle - Front Close(Prelim)

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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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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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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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