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Bison Gear and Engineering Term Glossary

Form Factor – In electrical engineering, form factor describes the stress induced by an electrical signal on a DC motor. The lower the form factor, the better the product will perform. Some advantages of a lower form factor are longer brush life and a cooler running motor. Traditionally, a form factor of up to 1.37 is considered acceptable.

To measure the form factor of a DC power supply, you will need an ammeter with both DC and RMS capability. Connect the ammeter in series with motor lead and take DC and RMS current readings. Then calculate form factor with the formula below:

Form Factor = amps RMS/amps DC

Gearmotor – A gearmotor is a combination of a motor and a gear reducer in one compact, easy-to-install system. Gearmotors allow for low-horsepower/high-speed motors to drive greater force upon an object by running the motor through the reducer; thereby increasing the amount of applied torque and decreasing the speed. This allows gearmotors to perform operational tasks in applications like conveyors, augers and automatic gates. Gearmotors at Bison are available in AC or DC formats and come in a wide variety of gear types, gear ratios, frame sizes and mounting features.

Gear Efficiency – Refers to how much energy is lost between gear stages due to friction. A gearmotor’s efficiency depends greatly upon the type of gears used and how many gear stages it has. For instance, in right-angle gearmotors, worm gear types typically create more friction between stages and have a much lower efficiency than hypoid gears.

To calculate gearmotor efficiency, use the following formulas:

Parallel Shaft Gearmotors

Gearmotor efficiency = .96N
Where N = number of stages

Right Angle Gearmotors (Worm)

E = (74-.66mg)/100
Where mg = gear ratio

Gear Type – Gears come in several shapes, sizes and variations. Bison uses the following:

Spur – The simplest type of gear. Spur gears consist of a cylinder or disk with the teeth projecting radially. The edge of each tooth is straight and aligned parallel to the axis rotation. They can only be meshed together correctly with parallel shafts. Spur gears are typically used in Parallel Shaft gearmotors and have 95% efficiency per gear stage.

Helical – Helical gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Helical gears can be meshed in parallel or cross orientations. The angled teeth of helical gears engage more gradually than spur gears, thus allowing for them to run smoother and quieter. Sliding friction between the meshing teeth can require thrust bearings and lubricant to compensate. Helical gears are also used in parallel shaft gearmotors and have 95-98% efficiency per gear stage.

Worm - A worm drive is a gear arrangement in which a worm meshes with a worm gear. Like other gear arrangements, a worm drive can reduce rotational speed or allow higher torque to be transmitted. Traditionally, worm drives are used in right angle gearmotors, and can be designed as self-locking. A disadvantage to worm gears is the potential for considerable sliding action, leading to low gear efficiency (between 30-70%).

Worm gears can be considered a species of helical gear, but its helix is usually somewhat large and its body is usually fairly long in the axial direction.

Hypoid - Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect. Hypoid gears are almost always designed to operate with shafts at 90 degrees. Hypoid gears are incredibly smooth and gradual, but also have a sliding action along the meshing teeth as it rotates and therefore usually require some of the most viscous types of gear oil to avoid it being extruded from the mating tooth faces. Hypoid gears have shown to be 4X more efficient than worm technology.

Bison currently manufactures some of the most advanced hypoid gearing worldwide, allowing for incredible efficiency in our PowerSTAR hypoid gearmotors.

Ingress Protection or IP Ratings – IP stands for Ingress Protection, and constitutes a set of classifications for various degrees of protection against solid and liquid contamination in your product, which in our case is the gearmotor. This includes, but is not limited to, dust, dirt and water. IP ratings are generally four digits. The first two are just IP, once again meaning ingress protection. The second two digits are numbers that signify the rated level of protection. The first number rates the level of solid object protection, such as dust or small particles. The rating goes from zero to six. Zero meaning no protection and 6 meaning completely dust tight. The last digit is also a number that ranges between zero and eight and represents the level of protection the gearmotor has against the ingress of liquids: zero being not protected at all, one being protected against dripping water, five being protected against water jets and so on. Check out our MiHow2 Video for more information here.

Overhung Load (OHL) – A pinion, sprocket, pulley or crank mounted to a gearmotor output shaft exerts a force perpendicular to it. This force is called overhung load (OHL) and care should be taken to make sure the OHL does not exceed maximum load shown on the appropriate performance/rating specifications shown for each product. Note: the ratings shown on charts are for loads applied perpendicular to the output shaft at the center of key, or flat on the output shaft.

Shock Load – Shock loads are unusually heavy and/or erratically occurring loads. Examples of this include cubes in an ice dispenser clumping together or a large tree root that requires greater than average torque from a power rodder. In these cases application analysis is crucial! Understanding the application better could help identify a potential issue under shock load and thus require a higher rated gearmotor. Standard Bison gearmotors have little difficulty handling momentary shock loads as much as 200% higher than its rated torque.

Torque – The measure of how much a force acting on an object causes that object to rotate about an axis. Selecting the proper gearmotor is a matter of matching output speed and torque to an application’s needs. RPM is determined by the driven machine’s requirements and should be known. That leaves torque to be determined, which is calculated by:

T (torque) = F (force) X R (radius)

The following provides a practical explanation of how torque is calculated.

1.  Attach a pulley securely to the shaft of the machine the gearmotor is required to drive.

  1. Wrap a cord securely around the pulley and fasten the end to a spring scale.
  2. Pull on the scale noting the weight at the time the shaft begins to turn. Do this several times and average the reading.
  3. Then multiply the reading in pounds or ounces, depending upon the scale used, by the radius of the pulley in inches. The resulting figure will be torque either in inch-pounds or inch-ounces. Metric measurements, of course, may be used as well.
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