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- How to vary my torque with a power-off brake?
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How do I figure torque needed for my electromagnetic parking brake?
E-stops and slopes might mean more than you imagined.
The electric vehicle market is growing quickly. As it grows, the need for electromagnetic parking brakes also increases. Many designers are struggling with how to size their parking brakes, especially for safety. These are used on many vehicle types including: AGV, UGV, AMR, XTV, ATV, UTV utility carts and vehicles, golf carts, construction equipment, lawn and garden equipment, mowers, ag and off-highway equipment, and more.
Firstly, the parking brakes are safety devices. They have a few purposes. They apply holding torque when a vehicle is stopped. They also are relied on for stopping torque during loss of power, called e-stops or emergency stops.
Each application can be different and industry standards differ as well. There is no one-size-fits all solution. This is why it is important to partner with Ogura on the design of your drivetrain early in the design process. We experience new application designs routinely. We will identify the critical parameters of the design including, but not limited to, speed ratio of brake to wheel, slope required for parking, slope required for e-stops, distance or time required for e-stops, and the number of emergency operations over a lifetime.
There are two torque designations for power-off, spring applied, parking brakes: Static torque and dynamic torque. Dynamic torque is always less than static torque, and it depends on rotational speed. Dynamic torque is responsible for the stopping time/distance. Often, the dynamic torque required for e-stops will be the deciding factor for the torque spec. It depends on the design parameters set for that vehicle.
It is possible to calculate theoretical torque, but this will not compensate for any other frictional losses. The best way to determine other frictional losses in the system is to perform actual testing. Tires, depending on the type, can offer great resistance. Many vehicles use regenerative braking from their motors which assists in stopping. Bearings and gearing provide some inefficiencies as well. Ogura can work with you to make the quickest and most accurate determination for your design. At that point, a parking brake can be installed, tested and proven, and time to market can be quick with the smallest and lowest cost brake selected for the job.
While Ogura designs and manufactures many specialized brakes to meet specific application requirements, there exist some standard models. The MCNB series is rated up to 3 lb-ft (4Nm). The RNB and SNB series are rated up to 148 lb-ft (200Nm) static torque but other standard series such as Ogura MNB rate to 590 lb-ft (800Nm) or higher. Special considerations might include manual release mechanisms, special coil voltages, unique sizes, environmental protections, and more.
Benefits of using Ogura electromagnetic parking brakes:
- Safety
- Design experience
- Manufacturing capability
- Compact size and lower power requirements
- Customization and optimization
- Ability to integrate with motors or other components