Students from Bochum University of Applied Sciences in Germany have been building solar-powered vehicles for nearly two decades. Their next project just might be the most challenging one.

The team of 16 students is constructing a vehicle to tackle the demanding terrain of the Simpson Desert in Australia. They are taking aim at the Guinness World Record for the 224-mile journey, which stands at 4 days, 21 hours and 23 minutes. The record was established in the 2017 edition of the Bridgestone World Solar Challenge, and the students are hoping to set a new standard in the 2019 edition of the race next November.

"We wanted to take solar mobility off-road and use solar energy in an area it is suited best: the desert," said Birgit Reuter, one of the students on the team. "It was just a small step for us to go from an Australian road to the Australian desert. And, there are not exactly a lot of deserts in Germany."

The students will be challenged to build a car to stand up to difficult desert conditions. Besides the intense heat - temperatures can reach as high as 122 degrees - the vehicle and its components must withstand sandstorms, terrain variances, and the lengthy distance.

Desert temperatures average in the low 90s. The race travels along the "French Line" from Purni Bore to Birdsville in the Simpson Desert, which is the fourth largest desert in Australia. It is the world's largest sand dune desert with more than 68,000 square miles. It is known as an erg or sand sea, which is a broad, flat area of desert covered with wind-swept sand and virtually no vegetative cover.

Reuter said sand infiltration is one of the most vexing issues for the students. Sand acts like sandpaper when it infiltrates the vehicle, and could potentially damage some vehicle components. "The electric box will need to be tightly closed and all the outer parts need to be at least IP65," Reuter said. IP65 is a standard established by the Electro-Technical Commission for Ingress Protection, and that figure means the assembly is totally protected against dust ingress.

The vehicle the students are building is similar to a Dakar Rally car. In that off-road endurance event, vehicles encounter some of the same conditions as the race in the desert. Reuter said the students' vehicle "looks like a frog" from the back, which leads to the name for the solar buggy - "Froggee."

"We don't have any infrastructure in the desert, so we're charging within three hours via a 40m2 foldable solar array," Reuter said. "This is basically our charging station to go. The energy is stored in a battery, just like any electric vehicle."

The buggy uses Lithium Ion pouch cells for its battery. The 40m solar array consists of 144 panels and 1052 silicon cells. Its output voltage is 650V at 6kW and 9.2A. "With it, we can be fully charged within 3 hours," Reuter said. "We believe the buggy will be able to drive 100-150km on one charge, but frankly, we will just have to test it to see how far it can go."

Students have also been trying to solve issues with the car's axles and getting the components to work together. "The desert is quite demanding, and we frequently couldn't just take any parts that might fit the specs of the vehicle," Reuter said.

The buggy includes motor cables manufactured by igus. The Germany-based manufacturer of motion plastics runs its North Americans operations out of Providence, R.I. The high-voltage electrical system in the students' solar buggy is wired with the cables.

The buggy has two motors, one for each axis, and a motor controller for each motor. The cables connect the battery to the controllers and the controllers to the motors. In all, there are 10 cables on the vehicle that span a distance of 15 meters.

The chainflex cables are used for applications that meet requirements to handle mechanical loads. They are also shielded, oil-resistant, flame-retardant and are suitable for temperatures up to 176F. The shield in the cables was one of the key advantages in selecting the component.

"We needed a shielding in our motor cables because the motor controllers are inverters and bring out alternate current to the motors," Reuter said. "In this field, it is essential to have good shielding to prevent electromagnetic compatibility (EMC) problems. We needed cables that are very robust and durable and at the same time conduct 400 volts. Since space is tight, they also needed to be bendable."

igus, which is based in Cologne, brings the concept of "motion plastics" to life with polymer machine elements that drive and move. The company has offices in 35 countries and employs 3,800 employees. It has the largest test laboratory in the industry and completes more than two billion test cycles annually.

Reuter said the team is concerned how vibration over the challenging terrain will impact the vehicle. The students are also concerned about the heat. "The vehicle will get even hotter, especially when we are charging because the vehicle will not be moving," Reuter said. "We have a strong cooling system for that. All of the components need to withstand at least 122F which can be a challenge, especially for components like a battery."

The students come from a wide range of fields, including mechanical and electric engineering, computer science, business, economics, and sustainability. Reuter said team members are confident their car will stand up under the desert stress and set the new record. "Our vehicle is specifically made for these conditions, so we believe we will definitely be faster," Reuter said.

Thomas Renner writes for many U.S. trade publications on manufacturing, construction, building and other topics. He can be reached at [email protected]

Related Links
http://solarbuggy.hs-bochum.de/
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