Shell Mold Work

Nicole Schauser // // No Comments

Today we picked up the first of our new molds for Zephyr from Kreysler and Associates, who have been kind enough to continue their sponsorship of CNC and personnel time to machine our molds. After helping them out by clearing away all of the excess styrofoam, we transported the top and bottom shell back to Richmond, and got busy with a huge sanding session to smooth out any bumps and machine paths left on the mold surface. After months of staring at the Zephyr computer model, it’s extremely exciting to see the body of the car slowly take shape!

Sam standing in a sea of stryofoam

Sam standing in a sea of stryofoam.

The next steps will be to coat the molds with Duratec Styroshield (to protect the styrofoam, which reacts with the sanding primer) and then with Duratec EZ Sanding Primer. This will then be sanded and polished so that we can make female fiberglass molds that are extremely smooth. The final step is then to do the actual carbon fiber layup inside the fiberglass molds. Every bump and mistake will only magnify as we make the fiberglass molds and then our carbon fiber parts, so we are taking extra care to ensure our final parts will be shiny and smooth!

Our sanding party!

Our sanding party!

Last week Kreysler also machined 1/7th-scale molds that we are going to use as a practice for the real deal. Every step we have to do on our actual molds will first be tested on these so that we can iron out any mistakes before working on our full-size parts. The practice molds have all been sanded and are ready to be coated in Duratec. Check out how nice they look!

Small scale Zephyr molds.

Small scale Zephyr molds.


Thank You, Terminal Manufacturing!

Derek Chou // // No Comments
Terminal Manufacturing, TIG, welding, CalSol

Thank you Jimmy! CalSol loved the experience

Terminal Manufacturing graciously took some time out of its schedule to teach 11 CalSol members how to do Tungsten-Inert-Gas (TIG) welding on aluminum. A big thanks to Jimmy for being a terrific teacher and allowing each and every one of us to actually get our hands on the machine and weld. His concern over safety really hit home with us and we will be taking every precaution when we weld too.

Since our design involves welding thin wall, aluminum tubing to form the structural chassis, this training could not have come at a better time. We will be using this knowledge to move forward with the construction of Zephyr.

Again, thank you for your support!

TIG welding, welding mask, CalSol

TIG welding as seen through a protective mask.

Suspension/Chassis Team Updates

Derek Chou // // No Comments
A render of the suspension and the chassis of Zephyr.

A render of the suspension and the chassis of Zephyr.

Recently, the suspension/chassis team has been working hard on finalizing the designs for the structural components of Zephyr. Because of the hard work of our team members, we have been able to shave over 55 lbs overall from the suspension and chassis! Most of these weight savings have come from changes in material and optimization in designs.

Our previous car, Impulse, had a steel chassis which weighed 52 lbs, but Zephyr will have an aluminum chassis – the SolidWorks model currently weighs in at just under 30 lbs. The front suspension of Impulse was made primarily out of 6061 aluminum, while Zephyr will have one made primarily of 7075 aluminum. Though 6061 aluminum is quite strong, 7075 aluminum is stronger than some types of steel! This allowed us to drop the weight of the front suspension from 60 lbs to 30 lbs. As for the rear suspension, Impulse had a single rear wheel, and its rear suspension weighed 20 lbs. While Zephyr has two wheels in its rear, the combined weight of its rear suspension members is just 17 lbs. Through being conscious about weight savings, our car is slated to weigh under 400 lbs now!


A completed steering knuckle part for the front suspension (one of three).

A completed steering knuckle part for the front suspension (one of three).


Along with working towards finalizing designs, Brian Graf, Derek Chou, and Daniel Heywood have begun machining parts for the suspension in the past week. Several members of the suspension/chassis team are also in the process of getting machine shop training and aluminum welding experience such that we can increase our work rate, keeping us on track to a rolling suspension/chassis combo for Cal Day, April 20th, 2013!



Daniel Heywood working on a steering extension part.

Daniel Heywood working on a steering extension part.

Derek Chou working on a steering knuckle part.

Derek Chou working on a steering knuckle part.

The amount of material we are able to mill out is a big factor in weight savings!

The amount of material we are able to mill out is a big factor in weight savings!

One of the upper A-Arms of the suspension, waterjetted and ready to be finished.

One of the upper A-Arms of the suspension, waterjetted and ready to be finished.


Electrical Team Prepares for the First Electrical Iteration

Jack He // // No Comments

Over the past winter break and semester, the CalSol Electrical Team has set its foundation towards an improved and more reliable Electrical System on Zephyr.

Through the Fall 2012 semester, the Electrical Team has recruited a number of new members. To prepare these members ready for real Solar Car design, we have conducted a series of training sessions ranging from basic electronics, soldering to microcontroller programming and circuit design.

At the same time, the Electrical Team was also discussing about the improvements we are going to make from Impulse’s electrical design. Deficiencies such as the lack of efficiency in the traditional passive balancing technology and the frequently happening connector problem would be eradicated when Zephyr is built.

By now, we have decided on a lot of stuff that would make Zephyr a more robust solar car, here is a list of major decisions made:

1. Explore the possibility of self-encapsulated solar cells.

As you may know from Min Ju’s blog post, the electrical team is exploring the possibility of encapsulating solar cells by ourselves. This might give us an edge on both cost and efficiency.

2. Active Battery Balancing Technologies

It is essential to make sure the modular voltages is the same in a multi-module battery pack if one wants to maximize the pack’s efficiency. Traditional passive balancing technology uses resistors to burn excess charge from modules with higher voltage to even out the difference, which is energetically inefficient and creates lots of heat. However, alternative technology such as capacitor based active balancing technology could actively transfer the excess charge from module with higher voltage to modules with lower voltage. Although such operation itself also consumes energy, considering the huge battery pack (400+ cells, 29 modules) we have for Zephyr, the net gain in efficiency is positive.

We have tried chips from different companies that are able to achieve this and development board has been made to test out these possibilities, which will be manufactured in a month.

3.  Brand New Power Distribution System

Since Zephyr would be built with two rear drive motors, the power distribution system has to be different from Impulse’s. We have reviewed the power distribution system on Impulse and decided to have a completely new design for Zephyr.

Power Distribution System on Zephyr

The topology of the power distribution system on Zephyr (Credit: Allan Wang)

As shown by the above diagram (Credit to Allan Wang, Power Lead), the new system would have a special Distribution Box that splits the main high voltage power line into two separate lines to two motors, and accepts power input from MPPT (Maximum Power Point Tracker) that collect power from solar array. As a result, there would be separate control unit (the Cutoff board) in the distribution box, which listens to CAN messages and turn the contactors ON and OFF when necessary.

Besides the changes in high voltage system, there would also be a redesign on the low voltage system. The 12V system on the solar is used to power all different PCB boards that controls and monitors the solar car and communicate with external agents. However, running 12V over long distance would suffer from resistive voltage drop over wires and sometimes it prevents devices from functioning (e.g. the horn used to be not loud enough because the supply voltage could not reach its 12V nominal input). Therefore, we added a new device called Power Hub into the system, which takes the 12V input from the main DC/DC converter in the battery box with larger gauge wire and distribute the power to individual devices on the car.

The power hub is an intelligent power distribution device that has the ability to monitor the current and voltage on each output line and cut down the supply when the current is too large. Besides distributing power, the power hub is also a CAN node on the car that communicates with other on-board devices to decide when to turn ON/OFF a supply and reports power consumption data to Telemetry system. In such a way, lights, horn and any other devices could be controlled over network, which reduces the amount of wiring and complexity of control board such as HCI.

4. Self-designed MPPT

After purchasing Maximum Power Point Tracker (MPPT) from external venders for a long time, the electrical team has decided to build our own MPPT system which could be optimized for our array size and achieve higher efficiency and lower weight.

Thanks to Steven Rhodes, our previous electrical lead, a test board has been designed over the winter break and ready for production.


Body Design for Zephyr (Almost) Complete!

Jega Vigneshwaran // // No Comments

While many other Bear Engineers were taking a break from the rigors of UC Berkeley during Winter Break, the CalSol Shell team was busy optimizing the aerodynamics of its latest car, Zephyr.

Side View of Zephyr

The flow around the top of the car. Note blue areas depict regions of low pressure and red areas depict regions of high pressure.


Since building a model for each iteration of the design would be incredibly costly, we use a software called Computational Fluid Dynamics (CFD) to simulate the conditions our car would encounter in the real world, such as turbulence and crosswinds. We model our car in SolidWorks, run CFD, analyze the results, and make the necessary modifications before starting the process over again, with each iteration taking about 5-7 days to complete.

Solar cars produce a fraction of the power of gasoline-powered vehicles, and consequently, it’s of paramount importance to have a well-designed body. We began the process in May 2012 by identifying the aerodynamic shortcomings of our previous car, Impulse. The aerodynamics team then spent the summer learning the intricacies of CFD and surface modeling by testing out numerous different airfoil bodies. Once we returned to Cal in the fall, we hit the ground running by splitting up our team into smaller subteams responsible for the design of different components of the car, like the wheel fairings, canopy, and airfoil body. Once we integrated all the different components, we began the nearly two-month process of running CFD and making changes to the aerodynamics.

To put our predicted performance values into perspective, Zephyr is 250% more aerodynamic than the Volkswagen Beetle, 182% more aerodynamic than the Toyota Prius, 133% more aerodynamic than the Ferrari California & McLaren, and 25% percent more aerodynamic than our previous solar car, Impulse.

Canopy Flow Trajectories

The colors reflect the different pressure values on the canopy as the air flows around it. Each line represents a “stream” of air.


We are pretty much done with the design of our new car and will be changing our focus to manufacturing in the coming weeks and months. Unfortunately, our predicted drag performance is, well, just that—predicted. Imperfections in manufacturing and real-world annoyances (splattered bugs) will inevitably increase our net drag. But our goal for this semester, as we begin the building process, is to minimize the number and impact of those imperfections as much as possible (bugs will still be bugs and splatter on our car).

Steering Wheel Molds

Brian Graf // // No Comments
Sam Cohen with Steering Wheel Mold Designed by Parker Schuh

Sam Cohen with Steering Wheel Mold Designed by Parker Schuh

CalSol has been hard at work over our Winter Break touching up the designs on our shell, chassis, and suspension but in particular Sam Cohen and Parker Schuh on the Controls team have been working on creating a lightweight, carbon fiber steering wheel. To do this we first needed a 3D model of what we wanted the wheel to look like; this was designed by Parker and is shown below.

Steering Wheel 3D Model Designed by Parker Schuh

Steering Wheel 3D Model Designed by Parker Schuh


Once we had the model we needed to CNC (Computer Numerically Controlled) out the molds for the wheel in a high density tooling foam. This is a complex process using a 3-axis milling machine in the Etcheverry Student Machine Shop on campus. The bottom photo shows the process of spiraling inwards removing the proper amount of material as the ball end mill progresses. You can see Sam here holding one of the two molds that we machined – corresponding to the top of the steering wheel.

The next steps are to prepare the molds for the carbon fiber layup and for layup itself, stay tuned for updates on this awesome project!

Great work gentlemen!

CNC Machining of the Molds

CNC Machining of the Molds

Tuft Testing at the Alameda Naval Base

Nicole Schauser // // No Comments

Monitoring tuft behavior with a GoPro camera.

Yesterday we had the awesome opportunity to do some aerodynamics testing at the abandoned naval airstrip in Alameda, thanks to Makani Power. For those of you who don’t know, this is the same location that Myth Busters uses, though unfortunately (or perhaps fortunately), we were alone on this stormy day.

CalSol used the chance of having a flat, deserted, 1.5 mile long runway to get some data on the aerodynamic performance and rolling resistance of Impulse. For tuft testing, we attached small pieces of brightly-colored yarn to critical areas of the car (such as the leading and trailing edges, and around the canopy) and videoed the performance of these tufts while driving at high speeds. This allowed us to confirm CFD results generated by software and to see where the flow separated from the car. We also performed coast-down testing from high speeds to determine both aerodynamic drag and rolling resistance.

We plan to use this information to update our CFD environment to reflect more real-life conditions and to pinpoint improvements to make for our next car, Zephyr.

We had a lot of fun during testing and would like to thank Makani Power again for this great opportunity.

CalSol poses with Damon Vander Lind from Makani Power.

Impulse on Display at Chabot Space and Science Center

Brian Graf // // No Comments
Impulse at Chabot Space and Science Center

Here is a teaser for what is to come on November 17th at the Chabot Space and Science Center

The Chabot Space and Science Center is having a grand re-opening of Bill Nye’s Climate Lab on November 17th. CalSol was extended an invitation to not only help staff the event, but also to bring Impulse and have it on display throughout the event!

As kids come rolling into the facility they will get to see Impulse front and center in the entryway and for those that have never seen a solar car before it is quite the sight to see. Impulse is literally the kids’ first step of the day at their journey at Chabot because once they talk with us, we will give them a stamp on their lab dash cards, and they can continue on to learn more, play games, and attempt to win prizes!

CalSol is extremely proud to have been invited to and included in an event such as this, so thank you Chabot for the opportunity.

You can learn more about the event and the center itself here at their website:

We will see you there, and don’t forget to look for the students wearing CalSol shirts!

P.S. – As one more teaser to come by and check us out, the view from the facility is AMAZING.

View from Chabot Space and Science Center

View from Chabot Space and Science Center

The Next Generation

Marc Russell // // No Comments

This past weekend, CalSol took a trip out to our composites shed for a hands-on training session focusing on composite layups. We had a really great turnout with new and older members from both the electrical and mechanical teams coming out to learn about a process essential to making a competitive solar car.

Group photo after a successful training session! Look at how much fun people had!

The session was part of a continued semi-formal training curriculum that CalSol has been slowly developing and implementing over the past few years to educate our members on various topics necessary to designing and fabricating a solar car. Already this semester the mechanical team has held numerous workshops on a variety of topics from basic modeling using SolidWorks all the way to performing CFD (computation fluid dynamics) analysis. The training sessions serve to introduce CalSol’s newest members to topics that are not covered in their normal coursework or that they won’t see in the classroom for a couple of semesters.

Senior team member Alex Cuevas explains the importance of fabric orientation.

This weekend’s training had members carrying out a vacuum-assisted wet-layup of fiber glass under the guidance of three senior team members. While CalSol plans to move away from the traditional wet layup process by partnering with companies to carry out more advanced composites manufacturing techniques, yesterday’s training still provided new members with valuable skills and experience that can be applied in the future. Specifically, members learned the importance of pre-planning, neatness, accuracy, and how using different layups types (e.g., sandwich vs. laminate, peel vs. release materials) can dramatically affect the properties of the final product.

Due to the work done this weekend and at all the other training sessions, CalSol’s newest recruits are now ready to go and assist our current members in tackling the challenge of designing our next vehicle. From what I have seen, CalSol’s newest generation seems more than up to task of creating our safest, lightest, quickest car ever.