# Multipole Multi-Layered Magnetorheological Brake with Intermediate Slots
## 2 Design of MR Brake  
Following an exhaustive literature review, which facilitated a comprehensive understanding of the existing challenges and technological advancements in the field, the conceptual design phase of the MR brake was initiated. Three distinct conceptual designs were proposed for this device, namely: (1) a multipole MR brake with outer multi-layers, (2) a multipole MR brake with inner multi-layers, and (3) a multipole MR brake with both-side multi-layers. Figure 2 illustrates the design concepts for these three configurations.  
Each of these designs possesses unique advantages and limitations. The outer multi-layer design, for instance, offers a uniform stress distribution and a mechanical leverage advantage, which can enhance the overall braking performance. However, this design also presents a challenge in terms of heat dissipation, as the heat liberated by the coil may not be effectively dissipated. In contrast, the inner multi-layer design is relatively straightforward to manufacture and exhibits a high heat transfer rate. Nevertheless, this design also has a limitation, as the magnetic flux strength is not uniformly distributed across all MR layers.  
The both-side multi-layer' design, on the other hand, achieves a uniform distribution of the magnetic field, thereby overcoming the heat transfer issue. However, this design is more complex to manufacture, and the percentage of torque generated by the inner layers is relatively low compared to the outer layers.  
Figure 2: Block diagram of MPML MR brake with different configurations.  
After carefully evaluating the pros and cons of each design, the multipole MR brake with outer multi-layers was selected as the preferred design. This decision was based on the design's simple construction and high mechanical advantage, which are critical factors in achieving optimal braking performance. The outer multi-layer design also provides a uniform stress distribution and mechanical leverage advantage, making it an attractive choice. The proposed MPML MR brake design is presented in detail in Figure 3. This design builds upon [PERSON]'s earlier model of a multipole MR brake [20], incorporating key enhancements to achieve improved performance and efficiency.  
As shown in Figure 3, this design contains a stator, rotor, and MR fluid. The rotor holds two rotor plates. The stator includes an inner stator plate, an outer stator plate, six magnetic cores, and a stator casing. The MR fluid fills the gap located between the stator and rotor plates. The wires are coiled around every pole with the same turns but in opposite directions. Three oil seal bearings were used to hold the rotor and restrict the oil leakages.  
When applying the current input to the coils, the cores will become the electric magnetos, and the magnetic field will start from one pole and move to two adjacent poles and back to the original pole like a circle line. The magnetic field that is perpendicular to the surface of the MR fluid generates the yield stress. Additionally, stress restricts the movement between the rotor and the stator. This brake is an improved design of [PERSON]'s early design concept of a multipole single-layer MRB. The Shiao concept is not effective for the multiple layers option due to the lesser flux density in the outer layers. Therefore, axial slots on the rotor and stator plates were introduced for this multi-layer brake. As shown in Figure 4, small non-permeable pads were designed to tightly insert into those axial slots. Due to these axial slots, the flux bypass in the inner plates can be arrested, and more flux travels to the stator outer plate, as shown in Figure 5. This way, the flux density in the outer layers can be enhanced.  
Figure 3: Cut section view of MPML MR brake.