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.

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).

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.

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.

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.

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.

Design Changes

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

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.

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.

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.

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.

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.

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.

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

Ball collector basin skeleton

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)

Detail view of key unit/basin interaction

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 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.

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.

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!

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.

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.

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 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.

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.

After several iterations of the wheel-style ball dispensing approach, I decided to try a gating mechanism instead.  The main drawback of the wheel approach was the low throughput.  Only about 4 balls per second could be dispensed.  Xylobot, however, can play over 20 notes per second.  While Xylobot’s speed isn’t fully necessary, at least 8 balls per second is a reasonable goal.  The wheel mechanisms do not meet that goal.

The Solution

The basic idea of a single gate mechanism is that the stream of balls is free to fall out the end of its containing tube whenever the gate is open.  The trick is opening the gate for a short enough period of time to consistently allow only one ball to pass through the gate per activation.  In our prototype, the time required to let one ball through was about 40ms.  With delays to account for the return motion of the gate and the settling of the balls, the prototype gate mechanism could achieve a rate of 11 balls per second.

Design

The most important part of this design is constraining the balls to one dimensional travel.  This was achieved by basing the gate around an aluminum tube with an inner diameter of .5”.  The gate would be entering perpendicular to the direction of travel, through a hole in the aluminum tube.  When the gate is up the balls roll through, but when the gate is down the balls are unable to pass through the gate.

The gate itself is a cone of plastic.  The conical shape is important because any non-angled surface has the potential to jam by clamping on the top of the ball.

The plastic cone is attached to a pull-type solenoid with a spring return.  The built in mounting bracket on the solenoid is a great advantage, but the 3-4 amp power draw (at 12 volts) is a major disadvantage.  The gate is normally closed, but when powered the solenoid pulls the cone out of the way of the balls.

In the initial prototype the mechanism made a large amount of excess noise when releasing a ball.  Quiet actuation is important for a musical instrument because the sound of the ball hitting the vibraphone key needs to not be overwhelmed by any other noise.  The addition of an o-ring to act as a hard stop when the gate returns to the closed position should help to muffle the noise produced by the prototype.

The final integration of this mechanism (actually 30 of these mechanisms, one per key) will have the tube nearly vertical, with the gate at the bottom.  With balls feeding into the top of the tube from Mike’s hopper mechanism, the gate will dispense one ball at a time, allowing them to fall onto the key and play a note.

Renders

Side View

Isometric Render

Isometric Render with Transparent Tube