Robert

Chassis design for "Robert"

CAL Super Mileage Vehicle:

This is the project of our school club "Cal Super Mileage Vehicle''. We design and build fuel efficient vehicle to race in the Shell Eco Marathon competition which takes place every year during Spring semester. In that competition, we compete with other schools around the globe across four different continents to spread the awareness of alternative fuels and to foster the ingenuity of tomorrow’s engineers. We have in the past competed with several cars which we are really proud of. For Spring 2023, we are in the process of building a new electric vehicle called 'Robert' with which we will be competing in the competition. The preliminary design of our new car 'Robert' is shown in the picture above. I am the Powertrain Lead of our team and currently working on the motor mount of our vehicle.

Motor Mount:

The motor mount is a support system of structures designed to stabilize the electric brushless motor in the vehicle. It is important that the motor is mounted into the chassis in a safe and proper manner to ensure the output power of the motor is transmitted to the wheels with highest efficiency and allowable safety. When designing the motor mount, it is crucial to maintain tight tolerances in concentricity of support bearing and motor shaft so that there is no interference when the motor is vibrating and rotating to drive the vehicle. I, as part of powertrain team, also ensure easy and safe attachment of the subframe to the vehicle chassis that maintain all required clearances. We have to design the motor mount by keeping in mind that the motor shaft must be stable and in place when a great amount of torque is produced by the chain tensioner.

During Fall 2021, I along with my colleague initially proposed a motor mount design for review to the faculty members and the machine shop specialists. Our main goal for the design was to add extra support bearing in the middle of the shaft so that when the motor is running and there is extreme torque, the shaft is stable, strong and driving the wheels of the vehicle with maximum efficiency. However, the design was not successful as the cost of the manufacturing was calculated to be drastically high and the manufacturing procedure turned out to be a little too complex. A presentation of the proposed design is given below:

Design Review.pdf

Design Proposal Presentation for Motor mount

However, learning from that experience and reflecting on the feedback we received from the faculty members and shop specialists for our first drafted designed, we came up with much more simpler and compact design for the motor mount during Spring 2022 that can keep the shaft stable while ensuring it is easier to reach the system for maintenance. After analyzing and planning, we decided to get rid of the motor mount subframe because from past experience of our older cars it was known that with the subframe of the motor mount, it is hard to remove or access the motor in case there is any maintenance issue. Also, the subframe add way too much weight in the vehicle which is not worth for the support it provides. An image of the current motor mount design is given below. We have made the shaft shorter by getting rid of the coupling and the extra bearing that we initially thought of so that it can be more stable and strong. We have also designed an extra large support plate in the middle to hold the motor rigidly. That large support plate will also hold the drive shaft which will eventually drive the wheel. This design serves the purpose of two system without adding any extra weight to our vehicle. The current design that we have is also easy to manufacture and light weight to make the vehicle as efficient as possible. Our plan is to place the motor mount on the floor of the chassis, screwed to the top of an aluminum plate.

Current design of our motor mount

Back of the chassis design where our motor mount will be attached and secured

Current Plan:

Currently, during the Spring of 2023, we are working on building a test rig for the powertrain so we can test the stability of our motor mount design and our System team can run power test on our test rig with the motor. We have ordered the parts and are in process of machining them for building the test rig. Our chassis team is currently in the process of prototyping the chassis body with their preliminary design. So, if our test rig shows confidence in our current motor mount design, we can place our motor mount into the prototyped chassis body to see how stable it actually is and how efficiently it can run the back wheels. That will be our first prototype. Based on that prototype, we will make any necessary changes in our design.

Meanwhile, we are making repairs in the current car 'Lux' to make it competition ready for the upcoming Shell Eco-Marathon 2023. One of the tire blew up for this car which is currently in the process of repair. We are also changin the motor in Lux from Brushed motor to Brushless motor. We are also working in changing the motor mount of Lux to safely and securely adjust the new powerful Brushless DC motor in the back of the Lux. We are hopeful for a successful journey in this year's competition.