Andrew Burks

Tag: Testing

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.

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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.

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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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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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