Preliminary Design Review (PDR)

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School

California State University, Northridge *

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317

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Mechanical Engineering

Date

Jan 9, 2024

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docx

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California State University, Northridge Group 3 Team Members: Zach Minton Alberto Larios Jasmin Ortiz Jason Najarro Martin Gomez Ornelas Preliminary Design Report (PDR) What we want to achieve is designing a bearing that will roll more efficiently than that of a typical skateboard bearing (Max RPM 608-ZZ ABEC 1.0). To do this, we want to lower the coefficient of friction as much as possible, so that the frictional torque is lower than that of a typical bearing. The theory that we are following to properly analyze our bearing system is that objects rolling past each other produce less friction than objects sliding past one another; so the faster we can make the elements of a bearing roll, the less we can account for the factor of friction slowing the rotational movement. We will make improvements to the frictional torque of a ball bearing by changing the design to match that of a cylindrical roller bearing, more commonly used in manufacturing. We want to change our ball bearing design to a cylindrical roller bearing design because cylindrical rollers are known to be more resistant to forward rotational friction. We will use a standardized equation to analyze the frictional torque of both bearing designs we have, using the same values of physical measurements to design said model. The equation we can use to find frictional torque would be: T f = F ×f m × 1 2 D m Where F is the standardized load applied to the skateboard in Newtons ● Well say 667.233 for a 150 pound person f m is the standard coefficient of friction for varying types of bearings: ● Single row ball bearing f m = 0.0015 ● Cylindrical roller bearings with cage f m = 0.0011 ● Cylindrical roller bearing full complement f m = 0.0020 D m is the measure of the bearings inner bore, and outer diameter added together ( D m = d + D) ● Both inner diameter of bore, d, and outer diameter of the bearing, D, will remain constant ● Almost all skateboard bearings have an 8mm bore, 22mm outer diameter, and 7mm

width. As seen on our sketch we will have the same dimensions with slight differences for it, in order for the bearing to be convenient for skaters. As they will not need to get a specific wheel or skateboarding truck to fit the bearing ● We will use the inner and outer dimensions of a standard skateboard ball bearing to analyze our cylindrical roller bearings. We have seen other references online that state there are different coefficients of friction depending on whether we are analyzing the radial or axial load of a bearing, but we are not completely sure on if we should even bother analyzing the system in two-directions. From what is understood, the applied load on the bearing will only really affect the radial direction of frictional torque, being that the wheel of a skateboard doesn't move left or right very much when it is actually attached to a truck assembly. There is a small amount or horizontal movement associated with the wheels of a skateboard when it moves, but we are not sure if there's a standard method to analyze such when dealing with a forward system such as ours. There is also the factor of viscosity of lubricant in a bearing that can also be ignored by us, as there is no easy or standard way for us to account for the varying viscosity level of greases used in a standard skateboard bearing. The equation provided above does state that it is representative of bearings that “ are without seals, and with optimum lubrication ”, so that will be the criteria we will stick to for our mathematical analysis. The load will be a normal force applied from the ground to the wheel up to the “bottom” portion of the bearing. Another load to take into consideration is the load applied from the axle of a skateboard truck. Since the cylindrical axle of the skateboard truck is connected to the bearing, there will be a force applied to the inner radius of the bearing facing towards the ground when a skater applies force. Potential materials that will be involved in our design will be steel as it is cheap and durable, aluminum as it weighs less than steel, silver, and other types of materials. What we need to account for would be the factor of safety we need to stick to for our system as a whole. We can account for this by establishing the max force that can be applied to the bearing without disrupting the efficiency of its movement. Any other criteria that we must follow will also be included in our design analysis. Our results will be gathered from solidworks simulation using finite element analysis. Below is our initial design for what our upgraded bearing will look like. This is just a rough sketch, but it will be the basis for what we are going to make and analyze with varying materials on SolidWorks.

Group Calendar up to CDR ● (11/1) SolidWorks design improvement model completed ● (11/4) SolidWorks simulation results with different materials/boundary conditions done ● (11/8) Analysis of collected data, and finalized design revision amongst group ● (11/11) Calculations of and input of data into graphical representation ● (11/13) Completion of powerpoint/presentation for CDR ● (11/15) Presentation of research thus far References to Equations and Theories Cited Rolling Bearing Friction - Roy Mech , https://roymech.org/Useful_Tables/Tribology/Bearing- Friction.html . SMB Bearings , https://www.smbbearings.com/technical/bearing-frictional-torque.html .

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