Sky Claw - Gantry Style Robotic Gripper

Hello world!

This instructable showcases the components of the Sky Claw gantry style robotic gripper. It was developed by a few students in Terry Research Laboratory led by Dr. Benjamin Terry at the University of Nebraska-Lincoln. Sky Claw was designed and intended to be completely open source for anyone to replicate, modify, and improve. This project has been several years in the making and we are beyond excited to show the world our creation!

The link below leads to a GitHub repository containing the entire Sky Claw package. It includes: a 100+ page instruction manual, complete bill of materials, all SolidWorks parts/assembles/drawings, and data sheets. Everything is completely free and available for download.

https://github.com/SkyClawTRL/SKY-CLAW

Notes:

Make sure to download ALL folders

This project is not designed for beginners. Knowledge in basic programming, electrical wiring, and soldering is highly recommended.

The primary purpose of this robot is to provide an educational platform for teaching mechatronics. The benefits of this platform are:

1) It provides a diverse set of sensors and actuators:

• Sensors: limit switches, proximity sensor, linear potentiometer, rotary encoders.
• Actuators: Stepper motor, brushed DC motor, servo

2) It is 100% open source and uses common commercial off-the-shelf components. Also, we have complete solid models of all parts including drawings of custom-made parts.

3) All custom-made components are easy to manufacture. If a student breaks it, he or she can also easily repair it.

4) It has very simple kinematics so modeling is easy.

5) The hardware interface to all sensors and actuators is through a single 25-pin D sub connector which allows the student to design/use the driver and electronics package of his/her choice.

Sky Claw was designed and 3D modeled entirely using Dassault Systèmes SolidWorks software. The goal was to create a robot that was made of primarily laser cut parts (or 3D printed) and commercially available hardware. Thus, most of the fabricated parts are flat for ease of cutting or FDM/SLA 3D printing. The design aspect started with the frame where everything will be connected to. All subassemblies, illustrated below in this Instructable, can be built with just a hex wrench, screw driver, and magnet.

Sky Claw features a plethora of sensors and motors that include: pressure sensors, rotary encoders, 24V DC motors, proximity sensors, servo motors, stepper motors, and limit switches. Everything is neatly attached to a D-Sub that connects to an Arduino Mega. It can be used as an educational tool to learn how various electrical components function behind the scenes or as a fun project for enthusiasts. It is great for learning to code in the Arduino language to make the components its equipped with work.

The frame is made from two vertical 1"X1" aluminum extrusion profiles connected by three 3/8" 6061 aluminum bars for rigidity. These bars will require some machining to drill out the clearance holes for the t-slot framing nuts and rectangular slots to accommodate the extrusion profiles. Two 1/2" thick medium-density fiberboard (MDF) panels can be used as the feet providing stability. Advantages of using MDF panels are that MDF boards can be cut to any size and shape., are relatively cheap, and easily accessible at any local hardware store. The feet can be cut to any shape. But keep in mind, the extrusion profile and foot's center of gravity should be lined up for maximum stability. There is also an MDF handle bolted to the top bar for transporting Sky Claw.

The vertical translation's motion is controlled by a 24V DC motor in the right housing. The motor's shaft is coupled to a 3/8" lead screw. Lead screws are a trapezoidal-screw that when combined with a mating nut, can convert rotational motion into linear motion. They offer good axial stiffness, smooth displacements, and are usually self-locking which makes it a popular choice for vertical motion. For example, most FDM 3D printers (Creality Ender 3, Prusa MK3, Ultimaker 5, etc...) consist of one or more lead screws to regulate the Z-axis motion. The left housing holds an incremental rotary encoder that can measure the angular displacement of the lead screw. In the center

The horizontal translation has two carriage spindles that house the lead screws. This is the main connecting point between the vertical translation subassembly and horizontal translation subassembly. A NEMA17 motor drives a timing belt pulley system that translates the gripper assembly left and right in the x-direction. It rides on a sturdy chemical resistant anodized aluminum low-profile mini rail and fool-proof polymer slide from PBC Linear. A big advantage of using this setup is that it offers an affordable and compact solution, all while being industry standard sizes so interchangeability is not a problem.

Note: The horizontal spindle carriage (quantity: 2) needs to be machined from bar stock 6061 aluminum. These are the only two parts in the entire Sky Claw that needs to be machined from scratch.

The gripper assembly features a combination of laser cut parts and purchased hardware from several vendors. What makes the gripper assembly a bit unique is that one connecting rod is attached to a ball bearing and the other is attached to a rotary encoder shaft. This setup produces a passive or redundant degree of freedom. Both connecting rods and the gripper can swing freely without any restrictions.

The gripper is activated by the rotation of an HS-5645MG high torque servo and flywheel servo horn assembly. The angular displacement of the servo motor produces an approximate maximum end effector width of 3" and minimum width of 1.75". Each end effector is equipped with a FlexiForce A201 force sensor capable of measuring up to 111 newtons or 25 pound-force. Right below the flywheel servo horn is a VCNL 4010 proximity sensor. This is a light duty sensor that can measure distances up to no more than 200 mm, but 10-150 mm is recommended for more accurate results.

Lastly, the pully bearing guide is seated inside the rotary encoder housing and DC motor housing in the vertical translation assembly. This assembly guides the timing belt that activates the vertical motion. Advantages to using a timing belt and pulley include but are not limited to: precision without minimal torque loss, slip-proof, high mechanical efficiency, etc.

These are some wire management recommendations to keep Sky Claw clean and beautiful.

-One of the best solutions to organize loose wires is using drag chain cable carriers. They neatly tuck away exposed wires while minimizing horizontal and vertical translation motion restriction.

-The connecting rods in the gripper assembly have 5 slot cutouts for wrapping the pressure sensor and proximity sensor wires through. It adds a bit of flare to the aesthetic while keeping the wires neat.

-Attach a few cheap adhesive-back nylon cable holders to the back of the aluminum frame brace. Sliding wires into the provided hole prevents any cable sag that could potentially interfere with other parts.

-All the wires coming down and attaching to the D-Sub connector can be wrapped in plastic spiral wrap.