Fabrication

The following subsections provide step-by-step instructions for fabricating the individual actuators, the hand as a whole, and the control board.

Actuator Fabrication

Detailed steps to fabricate the actuators are below, but can also be found on the Popular Science website.

Materials

  • 7/16-inch inner diameter ribbed hose
  • 5/16-inch wood dowel
  • 1/4-inch outer diameter vinyl tubing
  • Small hose clamps
  • 1/4-inch hose barbs x 1/4-inch male threaded adapter
  • 1/4-inch hose barbs x 1/4-inch female threaded adapter
  • Electrical tape
  • Yellow Teflon thread tape
  • Long balloon (type 350Q)

Tools

  • Utility knife
  • Spring-loaded center punch
  • Drill press and 5/64-inch drill bit
  • Scissors
  • Flat head screwdriver
  • Hot glue gun 
  • Measuring tape
  • A couple of adjustable crescent wrenches

Assembly

  1. Insert the 5/16-inch dowel into the ribbed hose to hold it straight. Use the center punch to carefully punch holes between each rib in a line along the seam of the hose. Flip the hose over and repeat along other seam. Soft Robot Hand Actuator Fabrication - Step One
  2. Use the drill press to drill a hole at each center-punched location between the hose ribs, leaving the dowel in place to provide support. It is best to drill the holes on each side of the hose separately, rather than drill straight through. When you are done you should have a neat line of holes on each side of the ribbed hose. These holes will act as a stress relief and prevent the hose from splitting when it is flexed. Soft Robot Hand Actuator Fabrication - Step Two
  3. Remove the dowel and cut the hose into five 3-inch fingers with the utility knife. For each finger, use the utility knife to very carefully cut between each rib from the hole on one side to the hole on the other. Leave the first two ribs on each end uncut. Cut through one side of the hose only. It is critical that you do not nick the far side of the stress relief holes or you will reduce the reliability of the finger dramatically. Now the hose can flex in one direction more than in the opposite direction. Soft Robot Hand Actuator Fabrication - Step Three
  4. Insert another piece of dowel into one of the long balloons. Use it to gently feed the balloon into one of the fingers until the end of the balloon sticks out enough to grab it. Remove the dowel, and fold about 1/4-inch of the balloon tip over the rim of the hose. Secure it by wrapping a piece of electrical tape all the way around the tip of the finger. Soft Robot Hand Actuator Fabrication - Step Four
  5. Now feed the dowel back inside the finger from the non-taped end, but on the outside of the balloon. Insert it until it is just within two ribs of the tip of the finger. Fill the tip of the finger with hot glue, allow to cool, and then carefully remove the dowel. It was found that the fingers were more reliable when a small amount of hot glue was used to fill the tip of the hose and then secured with more electrical tape. This helped prevent the end of the finger blowing out during use.
  6. Use electrical tape over the end of the finger, covering the hot-glued end. Another wrap of electrical tape over this will seal the end of the finger. Soft Robot Hand Actuator Fabrication - Step Six
  7. Cut the open end of the balloon away, leaving about an inch beyond the end of the finger. Stretch the open end of the balloon out and over the end of the finger. Soft Robot Hand Actuator Fabrication - Step Seven
  8. Repeat steps 4 through 7 for each finger. 
  9. Use the yellow Teflon tape to wrap the threads on each of the male hose barbs. Thread each male hose barb onto each female hose barb and tighten firmly with the crescent wrenches. Then use more yellow Teflon tape and wrap each female hose barb several times around. The ends of these hose barbs should fit snugly into the open ends of each finger. Soft Robot Hand Actuator Fabrication - Step Eight
  10. Use the small hose clamps to affix each finger onto the Teflon wrapped ends of the five hose barbs. Soft Robot Hand Actuator Fabrication - Step Nine

   

Hand Fabrication

Detailed steps to fabricate the hand are below, but can also be found on the Popular Science website.

Materials

  • 1x6-inch board or other support material
  • 1/4-inch O.D. vinyl hose
  • Tape

Tools

  • Hot glue gun and glue sticks
  • Drill and drill bits

Assembly

  1. Use hot glue to firmly attach each finger to the end of the 1x6-inch board or other support (the prototype used a plastic toy gauntlet) to form a hand. (see picture)
  2. Attach a length of 1/4-inch O.D. vinyl hose to the open hose barb on each finger. 
  3. Secure the hoses to the board or other support using tape, or drill holes to allow the PVC tubing to be routed.
  4. Now the hand is complete, but it still needs a control system. Follow the instructions for the Control Board Fabrication. 

Control Board Fabrication

Detailed steps to fabricate the control board are below, but can also be found on the Popular Science website.

This is a complex project. Since your control board is a considerable investment in time and money, consider future expansion as you plan your build. For example, you may wish to buy an 8-port manifold and appropriate valves and fittings, so you can expand the board to control more actuators than then five you need for the robot hand project. 

You can download the schematic below from the link at the bottom of the page. Clicking on the image below will also load the image in your browser, and you can save it locally from there.

Fluidic Control Board Schematic for the Soft Robot Hand Project

Materials

Tools

  • Table saw
  • Pencil
  • Center punch
  • Drill and drill bits (13/64", 17/64", others sizes based on component dimensions)
  • Metric tap M 3-mm x 0.5-mm, standard 10-32-inch tap (other sizes based on component dimensions)
  • Soldering iron and solder
  • Wire stripper
  • Flathead and Phillips screwdrivers
  • Adjustable wrench
  • Lighter (for shrink tubing)

Assembly

  1. Lay out the control board. You can base your design on the photos, but adjust it to suit your own needs. It is convenient to have the power and controls near the edges where you can reach them. It is also convenient to have the Arduino Mega/Sensor Shield between the controls and the MOSFET power switches. The MOSFET modules should be close to the air valves/manifold. Power supplies can be placed wherever you like, but consider how power will be routed around the board. Fluidic Control Board Fabrication - Step One
  2. Cut the Sintra board using a table saw to a size to fit your layout. 12 inches by 16 inches should do. This will be the base of the control board.
  3. From the remaining Sintra board, cut one piece for mounting the controls (about 12 inches by 2¼ inches). Cut another piece for the power switches and indicators (about 2 inches by 6 inches). Cutting a curve on one side of each of these pieces lets you fit them more compactly on the base, and adds a touch of style. Fluidic Control Board Fabrication - Step Three
  4. Use a pencil and a center punch to mark holes on the two mounting boards for the 50-kilohm pots, switches, LEDs, power jack, and for the hex bolts that will mount the boards to the base.
  5. Drill the holes in the mounting boards. It is possible to tap threads into Sintra board if you want to screw the pots directly into the board, rather than use nuts to hold them. Use one “sacrificial” pot as the tap, if you don’t have the proper size tap to cut the threads (this may damage the pot).
  6. Use hex bolts and nuts to raise the two mounting boards above the base. Before you install any components in the mounting boards, line them up on top of the base where you want them. Using the holes you drilled for the hex mounting bolts as a guide, mark the base. Then drill 13/64-inch holes in the base and make threads using a 1/4-inch by 20 tap.
  7. The Arduino Mega and the MOSFET switches should be mounted using M 3-mm x 6-mm Phillips plastic PCB board fasteners. Mark, drill, and tap holes to mount them and the other components. The 24V power supply may be mounted with double-sided foam tape. The air manifold can be mounted with two 10-32-inch bolts or with the foam tape.
  8. Mount the 24V power supply, air manifold, MOSFET switches, Arduino Mega and Sensor Shield, and 6-gang terminal block to the base. The terminal block may be mounted with small self-tapping screws or with foam tape.
  9. Mount all the pots, switches, LEDs, and the power jack to the two mounting boards, but don’t mount the boards to the base yet. You have some soldering to do first.
  10. The schematic shown at the top of this page can also be downloaded so you can refer to it in higher resolution. Refer to the schematic to wire the six pots, the 12-position switch, and the SPDT switch on the control mounting board. Connect the wires as shown to the Arduino Mega Sensor Shield. Fluidic Control Board Fabrication - Step Ten
  11. Follow the included schematic to wire the 12V power jack, power switches, and LEDs for the power mounting board. Connect the wires as shown to the 6-gang terminal block. Wire the 24V power supply as shown, and connect the 12V power jack. Leave the power supplies unplugged from the AC wall socket for now.
  12. Mount the control and power boards to the base board using 1/4-inch hex bolts and nuts. For each bolt, set one nut flush to the base board and another flush to the mounting board from underneath. This will hold the mounting board firmly. Fluidic Control Board Fabrication - Step Twelve
  13. Run power from the 6-gang terminal block to the Arduino Mega and MOFSET switches. Check the schematic for details.
  14. Connect the digital out pins of the Arduino Mega Sensor Shield to the input channels of the MOSFET switches as shown in the schematic. Then wire the channel outputs of the MOSFET switches to five of the SMC air valves. Fluidic Control Board Fabrication - Step Fourteen
  15. Connect the 1/4-inch outer diameter vinyl tubing from the five air valves to the robot hand. Connect more 1/4-inch tubing from the input of the air manifold to your air compressor. You should set the output of your compressor to about 20 pounds per square inch. You may need to adjust the pressure from the air compressor to slightly more or slightly less, but this is a good starting point. Fluidic Control Board Fabrication - Step Fifteen
  16. Plug in the 12V and 24V power supplies. Turn on the 12V supply power switch only (for now).
  17. Download the the software sketch example in the attached text file. Change the file extension from .txt to .ino. Set up your Arduino programming software, connect to the Arduino Mega, and then compile and download the sketch to the Mega.
  18. Now turn on the 24V power switch. With the function selector switch in one position, you should be able to control each finger with one of the five pots. Try adjusting the duty-cycle pot to different positions and see how it works. With the function selector switch in the other position, the 12-position switch will control the position or motion of the hand.