String a number of gears together and significant additional gains can be made. Gears and pinions provide the mechanical advantage as a result of their different diameters. The most common use of this system is in screw jacks as they are required to lift exceptionally heavy weights and the finer the thread (pitch) the greater their mechanical advantage.įig 4. The problem is of course that the input force at the end of the torsion bar must move a long way for any significant movement in the weight. Standard screw threads have a helix angle of between 2° and 4°, giving a mechanical advantage of ≈1/Tan(3°) The mechanical advantage of a screw is based upon the angle of the thread helix. These include:ġ) a detached (hanging) pulley that will double the lift factor (Fʷ)Ģ) two sheave blocks that contains multiple pulley wheels with which the lift factor (Fʷ) increases with the number of pulleysģ) the use of screws or multiple gears to rotate an input pulley, which significantly increase the mechanical advantage but at a significant cost in relative movement Screw There are number of variations to the pulley system, all of which increase the lifting capacity but reduce the weight’s relative movement. With a smaller input pulley (or roller R) the lift factor (Fʷ) will be less than 1.0 which means that the weight lifted will be lower than the applied force but movement will be greater. With a larger input pulley (or roller R) the lift factor (Fʷ) will be greater than 1.0 which means that the weight lifted will be greater than the applied force. The Torque Pulley is the simplest of the pulley systems that gains its mechanical advantage from the difference in radii between the input and output pulleys ( R: r). The two principle systems are the Torque pulley and Sheave Blocks. The magnitude of the weight ( W) and its movement relative to the applied force ( F) are dependent upon relative lengths ℓ: L ( Fig 2) PulleyĪ grooved wheel (or roller R) capable of containing a length of cord or belting that, when pulled, rotates the pulley ( r). Movement at F will generate movement in W Mechanical Advantage: Pulleys LeverĪ bar supported at a fulcrum anywhere along its length about which it is permitted to swivel.Ī weight ( W) is hung at one end of the bar and a force ( F) is applied to the other end.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |