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SCANS

Pneumatic Bladder

Components needed:

Printed parts:

  • bladder mold parts
  • bladder cutting jigs

Materials:

  • Metal D-shaft
  • Rubber clamps
  • Plastic cups
  • Popsicle sticks
  • Dragonskin 20
  • Razor blade
  • M3 nuts (x3)
  • M3 Bolts (x3) [to hold clamp and PCB together] Equipment:
  • Thinky mixer or similar centrifuge
  • Heated vacuum chamber (optional)

Bladder Casting

Preliminary Steps:

Assemble the bladder mold by putting the metal D-shaft in through the thin mold cap and all the way into the hole in the bottom until it spans the length of the mold like this.

Step 1:

Mix the [grams] of DragonSkin in a plastic cup according to the manufacturer recommendations. Pour it slowly but steadily along the side of the bladder mold so that the silicone completely fills the bottom. It is better to pour on one side rather than over the top to ensure that there are no trapped air bubbles underneath the shaft. Once the mold is filled it should look like this:

Step 2:

Put the top of the mold on, pressing at an angle from the bottom. Clean the silicone with a paper towel and then clamp the mold so that it is at an angle like shown below. Dragonskin will cure at room temperature for [16 hours?] but you can optionally cure it in a vacuum chamber set to 140 Degrees F or 60 Degrees C set to 80 Psi for 1 hour.

Step 3:

Once finished, pull the finger and rod out of the mold completely and gently back out the rod about an inch like shown below. Mix up another [20 grams?] of Dragonskin and pour it into the cavity. Again it is beter to go slowly to reduce trapped air. Put the lid back on and clamp as before, but cure with the newly-cured part sitting upright.

Step 4:

Once cured, remove the bladder from the mold, and pull out the metal core. Trim the finger tip to have [12 mm?] remaining after the chamber inside the finger ends. Once done, measure [120 mm?] and mark completely around the finger with a marker. Using the 3D-printed guides, slowly work down the finger with a razor blade until you reach the mark. Then using the 5 degree guide, trim the bladder until the end terminates in an angle like so:

Assembly with Clamp

Step 1:

Before clamping down on the open end of the bladder, we will coat all contacted surfaces with Sil-Poxy to ensure an airtight seal. Using a small brush, apply a generous amount of silpoxy to the D-extrusion of the clamp back. Additionally apply some to where the cut edge of the bladder will contact, and then apply a little around the final edge of the bladder. [pictures]

Step 2:

Insert the clamp back into the bladder, then bring the upper and lower parts of the clamp together around the bladder end. It can help to screw in the two bolts in the clamp top slightly at first to keep both halves from moving, while you get the SMA connectors through the holes of the clamp back. Insert the three long clamp bolts through the holes in the clamp back and screw nuts on them.

Step 3:

While applying pressure with your thumb to the clamp back, slowly tighten the two bolts in the clamp top until the two halves are brought together. You may need to alternate between screwing in those bolts with pulling slightly on the bladder to ensure that the clamp back is aligned. Once fully tightened, also tighten the three long clamp bolts so that the entire assembly is tightened while the Sil-Poxy sets. Allow to set for 30 minutes.