Friday, May 30, 2014

2014-05-29 (Th) Tennis Ball Launcher


Sometimes the project I work on is decided by what I’m currently excited about.  Sometimes a project is at a really exciting stage where a lot is getting done.  Other days I feel like there are external circumstances that have to be taken into consideration like if the summer is ending and I’m working on a longboard.  Finishing a longboard in the winter is fine but I can’t ride it until spring.  Sometimes I talk with someone about a particular project and later I enact the things I talked about.  At lunch I talked with the person behind the Tennis Ball Launcher contest and showed off what I had already built.

That evening I planned to continue work on the ESPeri.Impass, as I had been for the last several days, so I bought parts at a hardware store and was pretty excited about improving the new design.  However, when I got to the hack space I realized that I had forgotten the Impass materials at my apartment.  Everything except the parts I just bought was sitting on the table next to my bed.  So, suffice to say, I worked on the Tennis Ball Launcher because those parts were handy.

I guess there’s an advantage to a messy car, I would have been out of luck if that project wasn’t close.

Enough background.
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2” PVC was cut to obtain two pieces 30” long.  It was cut on a radial arm saw.  The goal was to make larger diameter replacements for the 1 ½” PVC already cut and drilled for this project.  Marks were made 1” from the end to be drilled to 5/16” for the carriage bolts which hold the bungee cord.  The 5/16” holes were drilled all the way through the PVC pipe.  Care was taken to keep the holes on the same plane.  One end was drilled then a bolt was inserted so an accurate ling-of-sign could be drawn at the opposite end of the pipe.  A second hole was drilled 28” away which is a longer distance than the first pipes.  This caused more tension on the bungee.

 Cutting the PVC into 30" pieces

The hole location is 1" from the end just like the first version
The holes are drilled all the way through the PVC pipes

 Lining up the holes at the far end based on the location of the first bolt

 Measuring 1" from the back end

Keeping the pipes close to identical was done by inserting a long 5/16” bolt through the first holes then copying the other end ensuring the holes in both tubes were the same distance.  The second end was marked by twisting a bolt through the first pipe, which had all the bolt holes drilled, and pencil marking on the second pipe.

 The pipes are fastened together with a long 5/16" bolt

Pencil marks are made to drill the same distance from the first hole
The holes will be very close to the same distance on each pipe

The next step was drilling 7/8” holes in the PVC for the pulleys and bungee to pass through.  The holes from the first pipes were copied by laying the pipes together and making marks where the holes began and ended.  The 7/8” drill bit was lined up to make the edge stop at the mark.  A rotary tool with a sanding drum was used to complete the hole and smooth over the edges of the hole.

 Marking the holes based on the first version

Two 7/8" drill bits.  The Forstner bit on the left was used in this project

Two holes made with the Forstner bit
A sanding drum in a Dremel is used to finish the holes

The sanding was done in a vacuum tube to minimize dust

The bungee was reinstalled along with the pulleys.  There is considerably more tension on the bungee cords.  It may be important to redrill the holes at one end of the PVC and lessen the tension.  It would also be possible to install a variable tension system to make the power adjustable.

To do:
  • Build:     Ramp (1/2 pipe)
                         Handle
                         Trigger
                         Mounting
                         Well ball sling
  • Attach release mechanism 
  • Test 
  • Refine 
  • Document

 Journal page 1


Journal page 2

Thursday, May 29, 2014

2014-05-28 (W) ESPeri.Impass

Safety is important to me.  Honesty is important to me.  I'll be honest, I was not safe today.  I needed some ring magnets to have a larger inside diameter and I maaaaaaaaaaaaay have jammed a tiny magnet under a moving drill press with my bare hands.  And I maaaaaaaaaaaaay have done that three times.  I didn't want to risk chipping the magnet casing by clamping it so the next logical solution was that holding a heavy metal with my bare hands under some sharp spinning metal was a good idea.

Yup.

Enough background.
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Two segments of aluminum bar stock were cut from an on-hand stock.  It was cut on a horizontal bad saw and smoothed on a belt sander.  The pieces were clamped together and drilled with a 9/64” drill bit to accommodate a #6 bolt.  Three ring magnets were also drilled to 9/64”.

Measured lengths of aluminum
 
Drilled pieces of aluminum
 
Drilled magnet

The magnets were put on a 2” long stainless steel bolt along with brass nuts and an aluminum spacer.  The spacer was removed and placed in a clamp to be given divots.  Two marks were made with a permanent marker so it could be determined that it was vertical since only divots would be made in the each side of the spacer.  After the first divot was made the spacer was spun 180° and a second divot was made.  The divots were made using a standard 135° point drill bit.

First stage of the spinne

 Vertical marks on the spacer

Divots made on a spacer

The spacer was placed back on the stainless steel bolt as well as the brass nuts and magnets.  The divots were made on roughly the middle of the spacer but this could not accommodate the balance point of the spinner.  Two more divots were made in the same way but towards one end of the spacer.

Placement of the divots on the spacer

Second set of divots

Two brass bolts had their ends sharpened to points so they provide minimal friction while holding the compass spinner.

Sharpened bolts

The balancing point of the spinner was found and the spacer was adjusted accordingly.  The balanced spinner was placed on the aluminum pieces to gauge how far out to make the next hole in the aluminum.  The compass was assembled and the spinner was balance more accurately on the divots.

 Rough balance of spinner

Gauging the distance to the next hole in the alumimum
 
Assembled compass

The spinner was able to move relatively freely but didn’t act as a suitable compass.  The divots may be too flat causing the sharpened bolts to wander and unbalance the spinner.  A drill bit may need to be ground down to provide a different shaped divot.

The bolt holding the aluminum pieces isn’t steady enough.  One aluminum piece was mistakenly countersunk which is partly responsible for the instability.  The holes should be redrilled and the bolt replaced with a ¼-20 brass bolt and brass nuts.

To do:

  • Buy a drill bit with a steeper point OR grind a drill bit to have a steeper point 
  • Redivot the spacer 
  • Replace cross-member bolt 
  • Buy brass nuts for cross-member bolt 
  • Test + Evaluate



Journal Page 1

Journal Page 2