Andrew Burks

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:

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.

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.

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.

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

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.

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.

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.