wEDGED Tutorial

ALERT: First Timers, please read the following pointers before switching on your brains.    Robot Making is an iterative process. KISS your Robot. No, I am not talking about actually kissing your robot, but generally for an amateur or a newbie this is the first and foremost rule, “Keep It Simple and Stupid”. One can think of thousand complex mechanisms for a particular job. But in the end, the simplest and the basic mechanism is the one that works well. Also keeping your robot simple, reduces the troubleshooting and repairing problems. Test your Robot. Only designing a robot doesn’t guarantee that it will work, you have to meticulously test your robot on various scenarios and make sure that the method you are using is foolproof. If it is not, compare it with other possible methods before finally choosing a mechanism. Make a test Arena. Arrange for a test arena “similar” to the one shown on the website, and practice with your robot. Make Modular Mechanisms: Construct each mechanism separately. This will help in arrangement/alignment of actuators according to arena; managing power supply separately for each mechanism, etc. This way, if one Module fails, the other is still working. It also results in reusable Modules for your future robots Don’t Panic. As Douglas Adams suggests, whatever may happen, even if a spaceship lands on your house and crushes your robot. DON’T PANIC. There is always another way. If ever you get stuck, Instead of kicking your robot, relax and think. What went wrong? And how can you correct it.

Now you are ready to go into details of basic robot Building.

Problem Statement

Let us first review the Problem Statement.

“The bot has to climb up a wedge of a pre specified inclination avoiding the bobs of the pendulum which will be oscillating with damped amplitude. There will be 2 such pendulums. At the top of the incline there will be swing with handle/hooks in it. The bot has to swing with the help of the swing to go from B to C. After reaching C the bot has to move into the victory zone.”

The Problem at hand can be easily divided broadly into two main tasks.

• Climbing the inclined surface.
• Holding the swing and swinging to lower platform

Climbing the inclined surface

For Climbing up the inclined surface you need a powerful drive base to carry your robot to the top. Now many would argue, why always wheels? Well if you are such a biped fan, go on with it, though I would remind you that keeping your biped balanced on an inclined plane is a bad idea and momentum will not be easily achievable. But then, you said you didn’t want wheels.

Though there are various kinds of drive bases, the most common Drive mechanism that can be used here is a Differential Drive. For more information on constructing a differential drive, you may check the link Differential Drive.

Since the plane is inclined, you have to keep in mind the mechanics of driving on it. This is pretty much similar to classic senior school physics problem.

As it is pretty much clear that there is a frictional force required to enable the robot climb up the incline. So the following factors will be determined keeping in mind the above information.

• The Weight of base
• The Wheels ( Wheel Grip and Radius )
• The RPM of motors required.

You can also think of a braking mechanism which manually(OR you can also think of automatic locking of brakes to restrict the backward movement of robot when ON the incline.) locks the backward movement of the robot when on the incline. This will save much of your time as the robot would stay where it is even on zero power, and also it will give higher control to prevent robot from getting hit by the oscillating pendulum.

But there is one thing that must be kept in mind, the robot has to avoid the oscillating pendulums so it must have swift movements, for this the controller should be very simplified, preferably devise a joystick-like controller, so that there is no confusion while driving the robot.

Holding the Plank and swinging to block C

The most important thing to concentrate on in this event is THE GRIP, which will eventually determine your robot’s efficiency. Since this is a mechanical event, it requires innovation. It is on you to design your mechanism and test it on the given scenario. When designing a gripping mechanism keep the following points in mind.

The following diagrams shows the two actuated clasps, which grip then handle of the plank.

• The two fingers are controlled with the help of two independent motors. In second case you use one motor only but the fabrication of this mechanism is very difficult.
• You can use any material for the fingers, ranging from aluminum metal pieces to toothbrush. For a better grip at point of contact, you can use rubber, etc.
• The motors used for actuating should be of high torque, in the range of 1.25 Kg-cm to 1.8 Kg-cm (50rpm to 30rpm).
• The motors used for driver base should be of high speed, in the range of 100rpm to 200rpm.

Since the robot has to support its own weight with the grip, and swing to the other side, the grip must be designed as to sustain the load, also the motor should be able to give enough torque for the robot to hang on to handle.
Since the destination platform is lower than the starting platform, keep in mind that when the robot lands, it can get overturned or even get disoriented, to prevent this keep your gripper at the maximum height in your robot. Also the un-gripping of the plank should be quick and at the right time, otherwise your robot can swing back and hit the first platform.