A solar-powered car with retractable carbon aerofoil profile

• What was needed: dryspin® trapezoidal lead screw nut with matching spindle, iglidur® plain bearing and xiros polymer ball bearing
• Requirements: Smooth running, lubrication and maintenance-free, no adhesion of dust and dirt, water-resistant, stability of aerodynamic and driving-related vibrations, no clearance
• Industry: Automotive industry
• Success for the customer: The energy of the car's solar battery is saved thanks to the rapid retraction of the carbon aerofoil profile. The low weight of the igus® component also increases overall efficiency.

The Innoptus Solar Team's project is to build a solar car every two years to take part in the Bridgestone World Solar Challenge in Australia. Due to recent changes in the regulations and after years of restrictions, active aerodynamics were once again permitted by the organisation. So ways were sought to actively utilise the wind's influence on the solar car to its advantage. One idea was to develop a retractable carbon aerofoil profile that could be extended onto the car depending on the angle of attack of the wind. This generates thrust, so that less energy is used overall and efficiency is maximised. The "fin" had to be a retractable system, as it is only useful when the incoming wind exceeds a certain angle of attack to the car. To achieve this, a linear actuated system was developed with a dryspin® spindle, carbon fibre rods and iglidur® plastic plain bearings.

Since the solar car drives in all kinds of environments, the positioning system for the fin had to withstand dry air and hot temperatures as well as rain, sand and dust, which can penetrate through the seams of the system. One challenge for the system was that it had to be installed in an existing solar car. This meant that there were restrictions on certain design parameters such as the length of the system, the angle at which it was mounted and the size of the fin itself. Another challenge was the weight. As solar cars should be as efficient and therefore as light as possible, the linear drive system had to be designed to weigh as little as possible.

The dryspin® lead screw was used to support the linear movement of the fin. Thus, the fin is moved up and out of the solar vehicle with the help of the dryspin® lead screw technology when the wind is above a certain angle of attack to the car. Thanks to the dryspin® technology, the bearing was able to withstand external influences such as water and dust during the 8-day solar competition in South Africa due to its self-lubricating specification. The spindle is supported by two xiros polymer ball bearings. The third component is a plain bearing: The iglidur® plain bearings were used to enable a tight yet smooth glide over the carbon rods. These also require no additional lubrication and are therefore low-maintenance.

The fin must be able to extend and retract from the solar car at any time while travelling at speeds of up to 120 km/h. This meant that the positioning system had to withstand both aerodynamic and driving-related vibrations. The best conditions for the screw drive used, which can be easily solved with the dryspin® technology. In addition, it was important for the alignment of the fins that the plain bearings had as little clearance as possible, which meant that a tight tolerance was required for the plain bearings around the carbon tubes. And weight reduction was not overlooked either: This meant using carbon rods, milling out unnecessary material from the plain bearing housings and using a plastic nut.