This instruct able is about a mini robotic gripper suitable for small robotic applications. This project was part of a assignment for the TfCD course in TU Delft.
The Gripper M.K.2 is designed to be used in small robotic applications to grip “small” objects up to 40mm in size and relative “light weight” up to 150g. It is relative small in size with dimensions about 48,5mm in length, 38mm in width and 41mm in height. The grippers max opening is 42mm.
Materials and design:
The gripper is composed mostly from PLA (Polylactic Acid) plastic, it’s designed so it can be 3D printed from a FFF (Fused, Filament, Fabrication) 3d printer. The design to account for the 3d printing imperfections utilizes bigger dimension tolerances and clearance between components.
Mounting and use:
It is designed to be mounted with a single M2 screw on the back or mounted directly on the horn of a ES08A mini size servo.
The M.K.2 gripper is composed from 17 parts: 6 plastic parts, 2 steel pins, 1 mini servo (ES08MA) and 8 M2 screws for plastic.
Mechanism and operation:
The mechanical operation design principle is one of the arm’s gripper is directly screwed on the servo horn with an M2 screw and by having a geared end it actuates the second arm to mirror its movement. The gripper’s arms uses free moving “pad” on their ends to conform to the objects shape and to increase surface area contact with the object that is gripped.
For this project a dedicated servo controller is used, Pololu Mini Maestro Servo Controller due to its high performance and ease of use.
1) Pololu Maestro Servo controller x 1 https://www.pololu.com/product/1353
2) ES08A x 1 http://www.emaxmodel.com/es08a-ii.html
3) AA batteries x 4
4) 3D printed parts of the gripper
5) 2 x 13mm (d,L) metal rods x 2 or (M2 x 13mm screws can be used too)
6) M2 x 5 screw for plastic x 8
7) General workshop tools, (screwdrivers, small drills 2mm, 2.5mm, soldering iron, etc.)
Step 1: CAD Model Design
First a 3D model of the gripper was made in parametric CAD modeling software in Solidworks.
The parts of the 3D model were saved in STL format to be 3D printed. Remember when saving an assembly of parts as STL in Solidworks, to go to Options and uncheck the option save all components of an assembly in a single file.
To get the STL parts download and unzip the file, Mini Servo Gripper
Step 2: 3D Printing
Orient the parts for 3D printing as shown in the pictures for better part quality, with support structure and 100% infill.
Step 3: Assembly
Assembly is pretty straight forward you will need a Philips screw driver and a small drill will be useful to clean the holes from the 3D printing. Do not over tighten the screws other wise the gripper won't have smooth motion and the servo will have to do extra effort to move the jaws.
If you pick the partial kit of the Mini Pololu Maestro servo controller you will need to do some soldering work.
For soldering a Sn60 Pb39 Cu1 solder was used and a soldering iron with medium tip at a temperature of about 350 degrees.
If you are new to soldering I recommend watching the following video tutorial. It is excellent to get the basics.
Step 4: Wiring
The wiring is straight forward you just have to connect the servo cable as shown in the diagram and the power connection in the lower right, Important remember the outer rail of pins is the ground.
The Working voltage of the EMAX ES08MA servo is from 4.8V~6.0V.
Connect the 4 AA batteries in series to get a combined voltage of 6V to power up servo.
The maestro board gets powered by the USB cable.
Download and install the Maestro Servo Controller software. (link bellow.)
Connect the Maestro with the PC and start the Maestro Controller Software and then enable the corresponding servo channel for your servo (in my case Servo channel 0).
The control of the servo is very easy just slide the slider and the servo moves. This software has many more advanced features such as servo sequencing but this is not going to be covered in this tutorial.
Step 5: Results
*(Some changed were made to the CAD model. The claws have a slightly different design now, so they are more flexible and can be easily attached to the servo horn. Also the gripper was 3D printed in white PLA to show better in the photos).
The gripper works as expected and has enough power to grab and hold small servos as show in the video.
It can be used as an attachment to many robotic application projects such as humanoid robotics, or robotic arms etc.
All in all it was a fun project that sets the basics for more advanced robotic projects, since the scaling up is pretty easy. Next project is a full 5 axis robotic arm, stay tuned :)