For our STEM Skills class, Hoang-Viet Tran, Joachim Kennedy, and I (Levi Evans) decided to construct a crane mounted upon a Roomba that would articulate its arm and bring a hook up and down.
Step 1: Acquire Materials
2. Perforated Wood Slats (2ft by 2ft)
3. Erector Sets (You can use wood, metal, etc. to build the pieces we used here. It's arbitrary.)
4. Assorted nuts, washers, and bolts
5. Metal or plastic spacers (long enough to cut off inch long pieces)
6. Spool of plastic string
7. 2x pulleys (rubber, plastic, etc. It's arbitrary.)
8. 3D printer (for the hook)
9. SparkFun Mini Inventor's Kit for Redboard
10. 2x Sparkfun Servo - Generic High Torque (Standard Size)
11. 2x Mini Spool (for mounting to servos)
12. iRobot Roomba Mounting Platform
13. Battery pack with AA batteries (for extra power to reroute to the breadboard of the Arduino
Step 2: Tools and Machines Needed
1. Needle nose pliers
2. Philips Head Screwdriver
3. Handheld drill
4. Drill press
5. Handheld jigsaw
6. Belt sander (optional)
7. Mounted bandsaw
8. Wire cutter
Step 3: Cutting the Wood
Mark the outline of the Roomba on your sheet of perforated wood. Cut this out with a bandsaw and finish it so that it looks nicer with a jigsaw and a belt sander. Keep the excess wood for the arm of the crane. Cut the excess wood into two 1 inch by 18 inches strips. These will form the two parts of the arm.
Step 4: Mounting the Chassis
Using the hand drill, make holes in the indicated spots to mount the metal chassis. You don't need to use these specific erector set chassis; you can make them out of any material such that you can mount the servos onto their sides and orient them horizontally. Also, you will need to leave room for the servos to be on opposite sides such that there will be room for both servos to spin. To accomplish this, we mounted another chassis behind the first one, which also made for a better angle and height for rotation.
Step 5: Connect Arm Pieces
Use bolts and cylindrical spacers to connect the two pieces of perforated wood that you cut earlier. Then bolt each piece of wood to the front of the first chassis.
Step 6: Mount the Wooden Platform
Once you have mounted the arm to the the chassis and the chassis to the wooden platform, you will need to mount the wooden platform to the designated safe-to-drill spots on the iRobot Mounting Platform, which is green. Mount a servo on the lower chassis to the right of the arm, attach a mini-spool to the servo's arm using the super glue, and thread the plastic string around the spool after tying it to the lower spacer on the arm. Mount a servo on the upper chassis to the left of the arm, attach a mini-spool to the servo's arm using the super glue, and thread the plastic string around the spool after tying it to the 3D printed hook on the arm (https://cad.onshape.com/documents/bb815c18b99687c53e45b176/w/d86f8e6da073dee48db1a675/e/f60ce94f6315725fb27f8bc5). Use bolts and nuts as spacers when you mount the servos so that they will not turn where they are mounted and thus waste energy. You will need to mount a pulley at the end of the arm and above the lower chassis as a means to guide the string and to decrease the amount of stress upon the servos.
Step 7: Wire the Servos and Program Them
See this pdf's Circuit #8 for the wiring for the servos to the Arduino.
Instead of wiring the servos to the arduino processor for power, you will need to plug in the AA battery pack into the positive-negative power entry section of the breadboard and feed the power to the servos through the pack, as the arduino cannot provide enough power for two servos. Use a handheld drill to enlarge the mounting points on the arduino, and then use bolts and nuts to mount the arduino to the wooden mounting platform. You can access our C++ code here: