The Gripper 3.0 is a precision CNC-machined end effector design for all of Parallax’s small robots. A single servo actuates the grab-and-lift motion with only a small amount of linear movement. The tension between the Gripper plates is determined by a torsion spring which also holds the plates down until the Gripper has closed from the initial servo movement. The remaining servo motion raises the object off the surface. The robot programmer only needs to determine the servos opened/lowered, closed/raised position, and the rate at which the transition occurs. The programmer needn’t consider the specific width of the object, just whether it fits within the Gripper’s paddles.
The kinds of objects the Gripper can pick up include 3D-printed cylinders, small wooden square blocks, and most lighter things about 1-½” in diameter and up to an ounce in weight. Take these parameters into consideration when designing autonomous robot contest rules.
Assembly requires about one hour and may be achieved by anybody with some hand tool proficiency and attention to detail.
You will need:
Your robot will be equipped to pick up and carry objects!
CNC machined aluminum parts:
Laser-cut parts:
Hardware parts
Miscellaneous Parts
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
The Base is attached to the Hinge with these parts, in order:
1-1/4″ screw > washer > Nylon spacer > Torsion spring over Spacer > washer > locknut
Once assembled, The torsion spring should apply downward pressure to the Base.
The assembled pieces should look like this:
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
An Arm connects each Finger to the Base, from the top side. Each Arm has three posts pointing downward: one on the thin end for a Finger, one on the geared end for the Base, and one in the center for the Idler Gear that slips between the Finger and Base gears. A Gear Plate on the bottom holds the pieces together.
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
Put the safety glasses on immediately! The Gripper has small parts, including a torsion spring which may be inadvertently released during assembly.
Note that this step has slightly modified instructions if you are using a Shield-Bot with Arduino.
With your robot powered down, turn the servo slowly by hand to see how the parts of the completed Gripper work together.
Foam pads on the inside of the paddles will help the Gripper hold onto smooth objects.
You can always remove the foam residue with rubbing alcohol and a paper towel. Your local hardware store has a variety of foam types available in the window and door insulation department, if you wish to experiment with other options.
Prior to doing any programming to open and close the gripper, the servo horn should be centered within the servo’s range of motion – in the middle with 90 degrees of motion on either side – and the Gripper in the closed, lower position as shown below.
Parallax hosts many tutorials for controlling a standard servo. Regardless of the microcontroller you are using, the following is always true for the Parallax Standard Servo which rotates 180°when mounted on the Gripper:
Below is a sample project in Makecode to test your gripper out.
