robotmatrix.org

 Introduction

• Objective: To build a long, multi-jointed, tentacle-like robot arm with a wand as the end effector. When the program is executing, the robotic arm dips its wand into a bowl of bubble solution and with gentle acceleration, it sweeps out a pair of large bubbles. The arm then continues and repeats the action.
• Parts:
  • Robix Rascal Robot Kit/Construction Set
  • The Bubble wand: made of malleable wire from craft store or florist. Wires are 1/16" (1.6 mm) and 1/32" (.8 mm).
  • Plastic Bubble solution bowl: approximately 9" (23 cm) in diameter by 5" (13 cm) deep.
  • Bubble solution: 1 gallon / 4 liters large-bubble solution is found at toy stores.
  • Electrical tape to hold wand to link.
  • Weight to keep base from tipping.
• To learn: This project can be messy but it is worthwhile as it demonstrates the superior repeatability of the robot when compare to human. The robot makes 2 sweeps in each direction, 4 in all. Each sweep makes two bubbles with the second bubble floating to the backdrop and breaking in nearly the same place each time. The robot can do this many times accurately in succession.

 Step 1: Making Gripper/End Effector

• As a simple hoop does not hold enough bubble solution at the edge to make good bubbles, thus, when making the wand, make sure that the smaller wire is spiraled around the larger. These spirals imitate the "fringes" found on bubble wands.
• Try the wand out by hand with the bubble solution. We found that stirring the solution to make it froth a bit helped to produce more consistent bubbles.

 Step 2: Assemble and build the Snake Robot Body and Muscle

• Assemble the bubbler robot and servo motors as per drawing (with one less link shown).
• You will need to clear and mark off a large safety area to accommodate the reach of this robot, which is about 20" (about 50 cm).
• You may need weight to hold down the base so it does not tip when the arm extends fully. Don't use a book, as it will get water- and soap-damaged.

 Step 3: Bubbler Robot Control and Programming

• Avoid overstraining the servos with quick stops of this arm, by doing so, we can reduce servo gear life or can break a gear outright.
• To minimize splashing of soap solution, program the dipping and sweeping actions with an empty bowl.
• The dipping action of this robot, as built, involves not just a single axis but several at the same time. This dipping position is not necessarily the same as the starting position for the sweeping motion that produces the bubbles.
• Since the extended arm has considerable momentum, use the lowest values of accel/decel which will give good performance. Start with these accel/decel and maxspd settings, then experiment for better bubbles.