Thank you, NXP!

Steven Rhodes // // No Comments

We’re proud to welcome NXP as a new sponsor!

The brains of a solar car are essential. For our designs, we use a distributed network of a handful of microcontrollers. Each node in our network controls something different, such as managing the batteries, controlling the motor, or taking all the input from the driver. An important decision is choosing these brains, and we have reached out to NXP for their help. Last December, a few members of CalSol went down to NXP to show off Impulse and talk about our plans for the future. We received a very friendly welcome, and we are hopeful of a bright future with them.

Our own prototype and the LPCXpresso

Our own prototype connected to the LPCLink portion of the LPCXpresso

One of NXP’s interesting products is their LPCXpresso boards. These development boards include both a microcontroller for rapid prototyping and a built-in JTAG debugger, the LPC-Link. This debugger gives us significantly more power than we have had previously, allowing us to step through our running code and see the complete state of the microcontroller!

NXP has given us 40 LPCXpresso boards and has agreed to provide microcontrollers and other integrated circuits as needed. The development boards have allowed us to quickly get up to speed, and we are already making our own prototype boards using NXP’s MCU’s. You can see one of our first boards with an NXP chip (made by team member Devan Lai) in the picture to the right. We are planning on using NXP’s Cortex-M0 LPC11C14 for many systems in the car. These microcontrollers only take a few milliamps to run, an incredibly low amount for how much power they have! This, combined with their integrated support for the CAN communication protocol, makes them well suited for our applications. As well, the move to a modern 32-bit ARM architecture allows our code to be both smaller and more efficient.

All of these improvements are incremental steps towards making our best solar car yet. We’re hard at work doing everything we can to increase performance, decrease power consumption, and maximize efficiency.

Thank you Dahl-Beck Electric!

Benjamin Chen // // No Comments


This past Tuesday, the motor team and several other members had the pleasure of taking a tour of Dahl-Beck Electric‘s motor repair facilities. Dahl-Beck is a local company based in Richmond that performs a wide range of repairs on industrial-scale electric motors brought in from customers around the world. They provide an incredible and invaluable service to clients who are able to bring in broken motors ranging from <1 hp to 10,000 hp and have them disassembled, evaluated, completely overhauled if necessary with new wiring and newly machined surfaces, enameled, painted, re-tested, and shipped back as good as new.

The CalSol motor team in particular is interested in Dahl-Beck’s ability to vacuum-impregnate motors with epoxy to ameliorate vibrations and insulate electromagnetic components. By requesting use of Dahl-Beck’s vacuum pressure impregnation (VPI) services, we could achieve a much higher quality potting of the current design of our stator than if we attempt to achieve it ourselves.

A big thank you to Dahl-Beck employees Kevin Sams and Dan Neal for taking the time out of a busy work season to give us a tour of their well-maintained facilities and chat about our motor project, and thank you to Mick Franssen of the UC Berkeley mechanical engineering student machine shop for introducing us to Kevin!

Be sure to check out photos we took on our Flickr.

Cal Day 2013!

Benjamin Chen // // No Comments

bnrThe annual Cal Day event is coming up this Saturday on April 20th and CalSol will be on display!

Cal Day happens every April and is a great opportunity for all of Cal to show off what it’s got in store, especially for visiting prospective students, and this year there are there are more exciting things to see than ever before. CalSol, in particular, will be showing our current car Impulse as well as newly built parts for our new vehicle, Zephyr. Our suspension and controls teams have been hard at work to display numerous vehicle components, newly machined and laid up, so make sure to stop by the Etcheverry-Soda breezeway all day to see Impulse on display! We will also be manning a table in front of the Engineering Student Services office for questions and information.

Click here to see a full list of Cal Day events hosted by the Department of Mechanical Engineering.


Hope to see you all there!

Unfinished lathe work on Zephyr's wheel hubs.

Unfinished lathe work on Zephyr’s wheel hubs. To see the finished results, come see them at Cal Day!

Waterjetted 7075 aluminum uprights for Zephyr's front suspension.

Waterjetted 7075 aluminum uprights for Zephyr’s front suspension.

Thank you Airtech!

Nicole Schauser // // No Comments

A sampling of donated Airtech materials.

We are super excited to announce that Airtech recently became a large materials sponsor of CalSol! The largest manufacturer of vacuum bagging and composite tooling materials, Airtech has generously donated some of their materials for our use on Zephyr’s shell. Since we have decided to go with pre-imprepregnated carbon fiber this time, we needed all new bagging materials that can withstand the elevated curing temperatures. We’ve also upgraded some of our other equipment, which will hopefully allow us to make an extremely nice shell for Zephyr.

Our new partnership with Airtech will give us the opportunity to improve our manufacturing process as we get ready to build CalSol’s most competitive vehicle yet. Thank you Airtech!

airtech adv materials logo blue and red

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).