Friendly Robot Hand

This is a five finger robot hand that does a "finger wave" when a human walks past. A garage startup is developing an open source humanoid robot (4.5 feet tall) that will be available this summer--I'm in line to receive one. This is my first attempt at constructing a five finger hand. It's a bit larger than I like and the cables are hard on the 3d printed plastic, but I think it has promise.

Supplies

(6) Waveshare st 3215 servo motors

Serial Bus Servo Driver Board

Arduino Uno

12 volt, 2 amp dc power supply

Stainless Steel Cable, 1/32 inch, and crimps

Human presence radar sensor

3d printed parts

Misc. 3mm screws

Grip tape

Springs

Step 1:

The serial servo motors each need their own address and they need to be set at the center position. Go to my instructable for details on setting them up. I chose these servo motors because they have magnetic encoders and should be more reliable than "brushed feedback" servos. The serial aspect reduces the wiring since only one control line is needed for all the motors.

Step 2:

1. Connecting the Take-Up Reel:
2. Use 3 M3 by 16mm screws to connect the take-up reel to the servo horn.
3. Use one M3 by 12mm screw to connect the wire that runs the finger.
4. Use the set finger Arduino program to place the reel at the 9:00 position when the servo motor is at the 3700 position.
5. Fasten the horn screw on the servo.

Step 3:

1. Preparing the Cable Wire:
2. Cut two 275mm pieces of thin cable wire.
3. Thread the lower wire through the end of the finger and crimp.
4. Thread the upper wire through the end of the finger and crimp.
5. Thread the lower wire through the middle finger and the upper wire through the middle finger.

Step 4:

1. Using the Setup Jig:
2. Use a special 3D printed jig with 12mm and 30mm screws to hold the setup for the finger.
3. Drill out a hole with a 1/8 inch bit--not designed into the setup jig.
4. Install the knuckle on the setup jig.
5. 
   
6. Connecting the Finger:
7. Use an M3 by 20mm screw to connect the end of the finger to the middle of the finger, serving as a bearing for the finger.
8. Thread the upper wire through the knuckle.
9. Install an M3 by 25mm screw through the knuckle as the bearing point.

Step 5:

1. Securing the Servo Motor:
2. Secure the servo and the servo motor mount using the four tiny screws included with the servo motor.
3. Install the servo motor to the rear of the test jig using 2 M3 by 20mm screws.
4. Fasten the extension spring (8.7mm diameter by 46.8mm long) to the top of the servo mounting housing.
5. Use an M3 by 12mm screw through the 3D printed washer to hold the spring.
6. Tightening the Cable:
7. Tighten the cable so that the finger is fully in the up position and crimp the cable.
8. For the lower cable, press the special crimp onto the cable, thread the cable through the lower pulley, tighten, and crimp the cable.
9. Remove the setup jig.
10. Final Assembly:
11. Use 2 M3 by 10mm screws on the front of the wrist and two M3 by 30mm screws on the rear of the wrist.
12. Fasten the finger and the servo motors.
13. Repeat this process three times.
14. Fasten the thumb as shown in the photos.

Step 6:

Attach the gripper tape. This tape is quite costly, but is very good for grippers.

You may notice that I put in pressure sensors and sensor wires in the thumb--that doesn't seem to work around the radius, so sensing will be a later project.