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Showing posts from August, 2009

### Improve math skills of your kids - Learn step-by-step arithmetic from Math games

Math: Unknown - Step-by-step math calculation game for iOS.

Math: Unknown is much more than a math game. It is a step-by-step math calculation game which will teach users how to calculate in the correct order rather than just asking only the final calculated results.

The app consists of four basic arithmetic operations which are addition, subtraction, multiplication and division. In order to get started, users who are new to arithmetic can learn from animated calculation guides showing step-by-step procedures of solving each type of operation. It is also helpful for experienced users as a quick reference.

Generally, addition and subtraction may be difficult for users who just start learning math especially when questions require carrying or borrowing (also called regrouping). The app helps users to visualize the process of carrying and borrowing in the way it will be done on paper. Once users understand how these operations work, they are ready to learn multiplication and division.

For most students, division is considered as the most difficult arithmetic operation to solve. It is a common area of struggle since it requires prior knowledge of both multiplication and subtraction. To help users understand division, the app uses long division to teach all calculation procedures. Relevant multiplication table will be shown beside the question. Users will have to pick a number from the table which go into the dividend. Multiplication of selected number and divisor is automatically calculated, but the users have to do subtraction and drop down the next digit themselves. Learning whole calculation processes will make them master it in no time.

Math: Unknown is a helpful app for students who seriously want to improve arithmetic calculation skills.

### Mechanical Power Transmission using Belt Drives and Chain Drives

Major types of flexible mechanical power transmission are belts and chains. Belts operate on pulleys or sheaves, whereas chains operate on toothed wheels called sprockets.

When to use chain drives or belt drives?

Electric motors typically operate at too high speed e.g. 1500 rpm and deliver too low torque e.g. 1.8 N.m to be appropriate for the final drive application. These figures are taken from 0.25 kW motor specs of some manufacturers just to get an idea. For a given power transmission, the torque is increased in proportion to the amount that rotational speed is reduced. So the method of speed reduction is usually required for normal mechanical power transmission system.

Usually, we use belt drives for first stage reduction because of high speed of the motor. A smaller drive pulley is attached to the motor shaft which runs at high speed, while a larger diameter pulley is attached to the parallel shaft that operates at a correspondingly lower speed.

" Usually, we use belt drives for…

### Philosophy of a safe design

Every design approach, we must ensure that the stress level is below the yield in ductile materials, automatically ensuring that the part will not break under a static load.

For brittle materials, we must ensure that the stress levels are well below the ultimate tensile strength.

Two other failure modes that apply to machine members are fatigue and wear. Fatigue is the response of a part subjected to repeated loads. Wear often happens where two parts are in contact with each other such as gears, bearings, and chains, for which it is a major concern.

source: Machine Elements in Mechanical Design, Robert L. Mott

### Chain Sprockets

Chain Sprockets are fabricated from a variety of materials; this would depend upon the application of the drive. Large fabricated steel chain sprockets are manufactured with holes to reduce the weight of the chain sprocket on the equipment. Because roller chain drives sometimes have restricted spaces for their installation or mounting, the hubs are made in several different styles.

Type A chain sprockets are flat and have no hub at all. They are usually mounted on flanges or hubs of the device that they are driving. This is accomplished through a series of holes that are either plain or tapered.

Type B chain sprockets has a hub on one side and extend slightly on the other side. The hub is extended to one side to allow the sprocket to be fitted close to the machinery that it is being mounted on. This eliminates a large overhung load on the bearings of the equipment.

Type C chain sprockets are extended on both sides of the plate surface. They are usually used on the driven sprocket where t…

### Chain Drives - Conveyor Roller Chain

Chain drives are an important part of a conveyor system. Chain drives are normally used to transmit power between a drive unit and a driven unit of the conveyor system. Chain drives can consist of one or multiple strand chains, depending on the load that the unit must transmit. The chains need to be the matched with the sprocket type, and they must be tight enough to prevent slippage.
" Chain is sized by the pitch or the center-to-center distance between the pins. This is done in 1/8" increments. "Conveyor Roller Chain
Roller chains are made up of roller chain link that are joined with pin links. The roller chain links are made up of two side bars, two rollers, and two bushings. The roller reduces the friction between the chain and the sprocket, thereby increasing the life of the unit.

Roller chains can operate at faster speeds than plain chains, and properly maintained, they will offer years of reliable service. Some roller chains come with a double pitch, meaning that th…

### Dowel Pins and Locating Pins

Dowel pins are the fasteners used to secure two parts together. They are available in both Metric and English sizes, and carry specifications such as diameter, length, and materials. Most dowel pins are made of stainless steel, plastic, , hardened steel, or ground steel. Plastic dowel pins are made of thermoplastic or thermosetting polymers with high molecular weight. Stainless dowel pins are chemical and corrosion resistant, and have relatively high pressure ratings.

Dowel pins are often used as precise locating devices in machinery. Stainless dowel pins are machined to tight tolerances, as are the corresponding holes, which are typically reamed. A dowel pin may have a larger diameter so that it must be pressed into its hole or a smaller diameter than its hole so that it freely slips in.

When mechanical design engineers design the mechanical components, typically they use dowel holes as reference points to control positioning variations and attain repeatable assembly quality. If no dow…