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#mEsh Tutorial

Untitled Document

Tutorial for #mEsh


This is a tutorial for the event #mEsh which is a part of ROBOTIX 2009, Annual Robotics Competition organized by students of IIT Kharagpur.
The task is to build a robot capable of climbing and descending a mesh. However there is a catch. Robot should also be able to maneuver laterally on the mesh. This is our attempt to get you started by introducing with claws, grippers and some other handy mechanisms. However, actual implementation of any mechanism will require fair amount of customization suitable to arena specifications.

There can be various solutions for this problem. The one which will be discussed here is the use of robotic “claw” or “gripper”. In the robotics world, hands are usually called grippers, they simply grasp or grip the object, hence the name gripper.

Gripper designs are numerous; each gripper technique has unique advantages over the others. Here we have outlined the TWO-PINCHER gripper design which you can easily use for your robots. It is fairly easy to build; even making use of inexpensive plastic toys. The gripper designs encompass just the finger or grasping mechanisms.


Gripping
Two-Pincher Gripper
The two-pincher gripper consists of two movable fingers, somewhat like the claws of a crab.
This model is really one of the most basic types of gripping mechanism. Its components are easily available and it is also very easy to build. Look at the diagram below. You just require 4 metallic pieces (or can be wooden or plastic), nut-bolts and some screws. Parts of Mechanix kit would come pretty handy.
The basic gripper is finished. In order to grip, you must move the two fingers. This can be done by rotating the angular shafts by motors.
Yeah, it can be as simple as this. After all, robot making is not a rocket science.


FIGURE 1 Two Pincher Gripper

Rack and Pinion
Another approach of designing a claw can be a sliding claw mechanism in which the two claws slide towards each other to close and slide away to open the grip. This can be achieved using a rack-pinion mechanism. Look at the diagram below. A rack-pinion mechanism converts the rotating motion of a motor to linear motion.
All you need is two sets of racks and pinions synchronized to move in opposite directions. Both can be controlled either simultaneously or differently to achieve the desired finger movement.


FIGURE 2.Rack Pinion mechanism.

Using Wheels
Most of you would think of using a wheeled robot to climb up the mesh. Yes, this is a possible solution and it is certainly easy in construction, but it may be a bit difficult sometimes to alter the direction of such a bot on a mesh and also braking becomes an issue. The success of a wheeled bot will primarily depend upon the ratio of the radius of the wheel to the mesh size as the wheel might get stuck in the mesh for lower ratios. For a wheeled model, the bot’s own weight might question its mobility at higher inclinations.

Robotic Arm
This topic in itself is quite vast and requires separate tutorial. So we are providing you links to some existing online tutorials. Mechanics of Robotic Arm Robot Arm using Potentiometers & Servos

Pulling its own weight
This will be an issue after the gripping. The gripping design should be suitably designed to support the weight of the robot. It can be simply achieved by pulling the body up by a powerful rack and pinion.

Braking
Braking a robot on a mesh is simpler task compared to braking on a plane surface. Here apart from the usual stalling of H-bridge i.e. giving same voltage at both the terminals of the motor, you can modify this stalling of motors to suit the mesh terrain. The easiest idea which can be thought of can be having prongs attached to the rear end of the robot. The prongs can be hooked into the mesh as per requirement and breaking can easily be achieved. You might also use pneumatic and other options to get attached to the mesh when required. Tumble-down mechanisms for descent are ruled out when mandatory stopping midway on the mesh is enforced.
These mechanisms are highly subjective. The more you innovate and think on variety of lines, the performance of your robot is bound to improve.

References

  • The Robot Builder's Bonanza - Gordon McComb
  • Concise Encyclopedia Robotics - Stan Gibilisco
  • http://www.grippers.com/
  • http://www.societyofrobots.com

Note:
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