Andrew Burks

Tag: Balls

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.


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.


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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Gate-Style Ball Dispenser

by on Sep.30, 2010, under RobOrchestra, Robotics Club, Vibratron

The Problem

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.


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.


Side View

Gate - Cross Section

Isometric Render

Gate - Iso Opaque

Isometric Render with Transparent Tube

Gate - Iso Transparent

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