Thursday, February 5, 2009

struktur Robot

Robot Structure

Robot Design Consideration
1. Bottom-Up Approach
2. Top-Down Approach
3. Bottom-Up and Top-Down
4. Budget
Bottom-Up Approach
A simple method
Detail design is unnecessary
Start from robot body construction
The use of power and weight is not balance
Final implementation does not fit robot contest requirements
Top-Down Approach
A relative complex scientific method
Detail design is necessary
Overall robot functions has been defined
Possible to construct in modular
Difficult to rebuild and redesign
Robot Materials Consideration
Light in weight
Easy to manufacture

Robot Structure
1. Plastic Robot Platform
2. Basic Wooden Platform
3. Building a Metal Platform
Acrylic can be used to build the foundation and frame of the Mini Robot

The best overall wood for robotics use, especially for foundation platforms, is plywood

The best overall wood for robotics use, especially for foundation platforms, is plywood.

Attaching the motor
The wooden platform you have constructed so far is perfect for a fairly sturdy robot, so the motor you choose should be too. Use heavy-duty motors, geared down to a top speed of no more than about 75 rpm; 30 to 40 rpm is even better.

If you have the right tools, working with metal is only slightly harder than working with wood or plastic.

Robot Materials
Types of Batteries

When you think “rechargeable battery,” you undoubtedly think nickel-cadmium—or “Ni-Cad” for short. Ni-Cads aren’t the only battery specifically engineered to be recharged, but they are among the least expensive and easiest to get. Ni-Cads are ideal for most all robotics applications.
Note that Ni-Cads can suffer from “memory effect” whereby the useful capacity of the battery is reduced if the cell is not fully discharged before it is recharged.

Nickel metal hydride (NiMH) batteries represent one of the best of the affordable rechargeable battery technologies. NiMH batteries can be recharged 400 or more times and have a low internal resistance, so they can deliver high amounts of current.

Nickel metal hydride batteries are about the same size and weight as Ni-Cads, but they deliver about 50 percent more operating juice than Ni-Cads. In fact, NiMH batteries work best when they are used in very high current situations.

Unlike Ni-Cads, NiMH batteries do not exhibit any memory effect, nor do they contain cadmium, a highly toxic material.

The battery in your car is a lead-acid battery. It is made up of not much more than lead plates crammed in a container that’s filled with an acid-based electrolyte. When the battery goes dead, recharge it, just like a Ni-Cad. Although lead-acid batteries are powerful, they are heavy.

Representative discharge curves for several common battery types.

The charge/discharge curves of a typical rechargeable
battery. Note that the charge time is longer than the discharge time.

You can obtain higher voltages and current by connecting several cells together. There are two basic approaches:
1. To increase voltage, connect the batteries in series. The resultant voltage is the sum of the voltage outputs of all the cells combined.
2. To increase current, connect the batteries in parallel. The resultant current is the sum of the current capacities of all the cells combined.

Memory effect in Ni-Cad battery can be altered in two ways:
The dangerous way. Short the battery until it’s dead. Recharge it as usual. Some batteries may be permanently damaged by this technique.

The safe way. Use the battery in a low-current circuit, like a flashlight, until it is dead.
Recharge the battery as usual. You must repeat this process a few times until the memory
effect is gone.

Battery Monitor
Quick! What’s the condition of the battery in your robot? With a battery monitor, you’d know in a flash. A battery monitor continually samples the output voltage of the battery during operation of the robot (the best time to test the battery) and provides a visual or logic output.

Gears and Gear Reduction
The normal running speed of motors is far too fast for most robotics applications. Locomotion systems need motors with running speeds of 75 to 150 rpm. Any faster than this, and the robot will skim across the floor and bash into walls and people.

Arms, gripper mechanisms, and most other mechanical subsystems need even slower motors.

The motor for positioning the shoulder joint of an arm needs to have a speed of less than 20 rpm; 5 to 8 rpm is even better.

There are two general ways to decrease motor speed significantly: build a bigger motor (impractical) or add gear reduction.

Pulleys, Belts, Sprockets, and Roller Chain
Akin to the gear are pulleys, belts, sprockets, and roller chains. Pulleys are used with belts, and sprockets are used with roller chain. The pulley and sprocket are functionally identical to the gear. The only difference is that pulleys and sprockets use belts and roller chain, respectively, to transfer power. With gears, power is transferred directly.


Pulleys come in a variety of shapes and sizes. You’re probably familiar with the pulleys and belts used in automotive applications. These are likely to be too bulky and heavy to be used with a robot. Instead, look for smaller and lighter pulleys and belts used for copiers, fax machines, VCRs, and other electronic equipment. These are available for salvage from whole units or in bits and pieces from surplus outlets.

Pulleys can be either the V type (the pulley wheel has a V-shaped groove in it) or the cog type. Cog pulleys require matching belts. You need to ensure that the belt is not only the proper width for the pulley you are using but also has the same cog pitch.


Sprockets and roller chain are preferred when you want to ensure synchronism. For large robots you can use 3/8-inch bicycle chain. Most smaller robots will do fine with 1/4-inch roller chain, which can frequently be found in surplus stores. Metal roller chain is commonly available in preset lengths, though you can sometimes shorten or lengthen the chain by adding or removing links. Plastic roller chain, while not as strong, can be adjusted more easily by using snap-on links.

The Clapper
The “clapper” gripper is a popular design, favored because of its easy construction and simple mechanics. You can build the clapper using metal, plastic, or wood, or a combination of all three.

Two-Pincher Gripper
The two-pincher gripper consists of two movable fingers, somewhat like the claw of a lobster.

Build A Robot

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