Despite the complexity of most of Sunswift IVy’s electronics sometimes a simple change can make a significant difference. As a new member of the Sunswift team my first job was to create a new driver display to replace the older display which while still functional was designed to sit inside the steering wheel, a position that proved uncomfortable for the driver. The new display reuses a 16*2 character LCD display from an older driver display and features LED covered wings acting as turn signal indicators. It will be mounted above the steering wheel, this will hopefully mean drivers will not have to bend their necks to see it. It is a very simple design, but not much else is required.

Since this project’s hardware is very simple and similar to that of CAN nodes already in operation, and since very similar displays had already been created by previous years of Sunswift this was really a great project to learn the basics of hardware design at Sunswift. I am new to PCB design but working with Sunswift has taught me a lot, and this little project has been a fun experience.

The display is not yet finished, the circuit board has been made but
is yet to be tested and software is yet to be written for this
iteration of driver display. Time to get to work.

Winning a race requires much more than a fast car– more often than not, winning a race comes down to logistics and effective communication amongst the team.

Over the past month, we’ve been working on a mobile app that allows the team to receive real time information related to the car and communicate with one another. The application currently displays a map of the solar car’s current location, battery state of charge, solar insolation, tyre pressure, speed, and the weather for the current location. By using the app, the team will be aware of what’s happening at all times and reduce chatter on the radio.

In addition to the mobile app, I’ve been working on the network infrastructure to support the application. Through a generous sponsorship from Benelec, we’ve had the opportunity to build a large mesh network between the solar car fleet. This mesh will allow the team to use the app and share information amongst themselves. This mesh network consists of a few SOHO routers installed with custom firmware and lots of antennas linking them together.

Any questions? Leave them in the comments!

Sunswift Ivy Mk2 will be rolling on a set of new lightweight carbon fibre wheels for the upcoming World Solar Challenge. As these new wheels are geometrically different from the current ones, we worked on designing a new set of wheel hubs to fit the new wheels to the car.

Design

The design of our new hubs was more of a modification to the old hubs rather than a complete redesign. As the front suspension and the uprights were to be left untouched for Ivy mk2, we had to keep the main dimensions of the hubs unchanged. Furthermore, we also had the added constraint of keeping the position of the brake disc unchanged.

The main difference between the new GHCraft wheels and the older wheels is that the mounting location of the wheels is offset slightly to the right from the centre of the wheel (looking on from the front). Therefore, the only major change we had to make to the general dimension of the hubs was the position of the shoulder at which the wheel is mounted.

Modifications were also made to ensure the hubs were as light as possible. We removed the ‘spokes’ that supported the brake discs, and shaved off bits of material we thought were unnecessary. The total mass of the new design is 0.793 kg, which is 0.205 kg lighter than our previous set. This adds on to the mass savings of the new wheels, making the new wheel assembly of Ivy mk 2 even lighter than before.

Old Hubs

Proposed new hubs

FEA

To verify the strength of our design, we performed a Finite Element Analysis (FEA) on it. The boundary conditions used for our analysis were set to the worst case scenario to ensure that the hubs would not be destroyed even under the worst circumstances. The results obtained were quite satisfactory as the stresses and deformations of the hub did not exceed the critical values. Also, our fatigue analysis proved that our hubs would last many WSC races.

FEA on the new hubs

The hubs are currently at a stage in which the design has been finalised. We hope to manufacture them as soon as possible.

By Sid Menon and Chin Godawita.

Since the start of the year, I’ve been working on the tilt sensor. Its purpose (as you are probably able to guess) is to measure the pitch and roll of Ivy mainly for use in roll down tests.

These roll down tests are used to obtain a power vs speed curve for the car by accelerating the solar car to a high speed and letting it coast to a stop. We can determine the drag forces by the rate at which the car slows down. An example power vs velocity curve is sketched below:

Power curve showing coefficient of rolling resistance (Crr) and coefficient of drag (Cd)

As you can imagine, any inclination or declination, or even relative wind velocity on the track will skew these results. The tilt sensor allows us to account for the inclination and declination using the tilt angle and the velocity of the car.

This is the second generation of our tilt sensor, our first one consisted of an accelerometer. Unfortunately while this is perfectly adequate when the car is stationary, the numbers are distorted as the solar car accelerates.

This is because the acceleration component on the forward direction made the accelerometer reading think it was actually tilting. This is the same effect as accelerating a glass of water on a table -the water level will tilt away from the direction of acceleration.

We aim to overcome these issues in this revision by incorporating a gyroscope with the accelerometer and using sensor fusion to combine the results. This will be done with complimentary filtering or kalman filtering.

The tilt sensor will also make use of the velocity data from the motor controller to help correct for the acceleration readings.

2011 Tilt Sensor board design

Tilt sensor board printed and populated

Charith Perera

Since our last carbon update things have been coming along extremely well with many hours dedicated to our composites work, plying our trade and improving all the time. To date we have produced 3 lower spats (fairings) and two upper spats and have another upper spat ready to be cooked tomorrow morning. The last few in particular have been turning out rather nicely as we become more accustomed to working with the wonderful stuff that is carbon fibre. The best bit is unwrapping it, while the moulds are still warm, and pulling out a nice shiny new part!

Over the next week we are planning to move on to laying up the canopy windshield, rear view camera and number plate offsets using wet layup resin. Once these offsets have been created  we can move on to cooking some bigger parts in the big oven as a trial for the top shell. There will be lots to learn when we fire it up for the first time. Lessons from the small ovens include, how to avoid melting lots of breather, how to avoid noxious fumes when trying to use high temperature foam core to stop melting the breather and how to cure parts in under 12 hours! Highlights from these learning experiences include staying in the workshop till the early hours of the morning while curing the first lower spat.

We have been enjoying the camaraderie of spending time in the workshop with the tunes blaring listening to Smoky Joe sputter away like clockwork.  I’d like to claim, on behalf of the carbon team, we have had the most fun out of any team in Sunswift and it all started on our first night out to some fine Lebanese dining. May the good times continue!

This next month we will be posting some personal reports from team members who will share the projects they are working on in the lead up to this Octobers World Solar Challenge. Today’s story is once again from the electrical team from one of our newer members, Rob.

Over the past few months I have been working on updating our GPS barometer module. While we still have one of the last version working, Sunswift would like to make sure there is backup for every piece of electrical equipment in the car. This means if something breaks, it will be a simple swap job, and the car can get back on the road quickly.

Building on the previous design, I have included a better GPS unit and a new barometer board which outputs atmospheric pressure and temperature. These will be used in monitoring the car and its position to assist in the strategy for the race. This module is an integral part of our telemetry network. Soon we will have a new way for members of the public to keep up to date with where we are, while on the race and in the lead up to the race, but we’ll have more news on that soon.

GPS Barometer PCB Board

As a newer member of Sunswift, this has been an interesting and challenging first project. The PCB is finished, (see the picture above) and the next stages are to print and construct the boards and then program the microcontroller. The microcontroller has been updated to include the CAN communications with the rest of the car. The GPS is being secured to the board more firmly to increase the durability of the module.

Rob Makepeace -Electrical Team