Due to the fierce competition in the world of solar racing, the Nuon Solar Team always makes the design of her latest car a well-kept secret in order to keep innovations for ourselves. With the Bridgestone World Solar Challenge now fast approaching we can slowly reveal more and more of the design of Nuna8. Today we begin to do so, starting with the basis of Nuna8: her suspension. This blog will detail on the suspension of Nuna8, and explain the design choices made by our mechanics Thijs Overwijk and Bart Helwig that led to this design.
For the full explanation we need to start around four years back, when the regulations for the 2013 Bridgestone World Solar Challenge were released. Back then it became clear that the BWSC organisation had implemented one of the biggest rule changes in years: for the first time in Nuon Solar Team history solar vehicles were required to have four wheels. As a consequence a brand new suspension for a four-wheeled solar vehicle was designed in 2013, with team Nuna7 opting for a revolutionary concept with leading arms and trailing arms rather than the traditional wishbone suspension. This new suspension allowed the aerodynamic department of team Nuna7 more design freedom in their topshell, giving them the opportunity to design a winning car.
Bart and Thijs’ task thus was to evaluate this new suspension concept for the second four-wheeled solar vehicle in Nuon Solar Team history. Surprisingly enough they eventually picked a radically different design than that of Nuna7, predominantly as Bart and Thijs were informed that Nuna7’s suspension had its downsides too. That does not mean though that the design of Nuna’s suspension was done and dusted quickly, as the mechanical design of a solar vehicle is subjected to quite some restrictions. “It is predominantly the aerodynamicists of the team who always want a smaller suspension, which fits as well as possible in the aerodynamic shape of the car. That always makes for a difficult decision, how far do you dare to go? Do you dare to make all components even smaller, causing forces in your suspension to increase?” explains Thijs. “When forces in the suspension increase the chassis has to be reinforced to cope with these forces, meaning the chassis gets heavier. All in all, coming to a final design was a difficult decision involving all disciplines of our design team”, Bart adds.
The result of this trade-off might be a surprising one for a layman: Bart and Thijs have chosen to replace Nuna7’s leading arm front suspension by a wishbone front suspension. According to Thijs this choice is the correct one for both performance and safety: “Wishbones pose less of a restriction for the aerodynamicists concerning the wheel covers than a leading arm concept, so they are better performance-wise. A wishbone suspension requires no space for a leading arm in the wheel fairing opposing the driver, meaning this fairing can be drastically reduced in width.” The choice for a wishbone front suspension has reaped rewards, as Nuna8 has reduced her aerodynamic drag by about 10% compared to Nuna7.
And that’s not all, Bart explains: “Last year’s experience showed that the leading arm front suspension used for Nuna7 was not as safe as we hoped. We attribute this to the fact that team Nuna7 thought of the concept themselves, with no known use in other applications. All in all, there was too little experience with such designs. Stabilising the suspension led to many problems, as we experienced the design’s behaviour changing over time. The wishbone concept has been reliable whenever we used it, even when Nuna3 drove 120 kilometres an hour for long stretches back in 2005.”
The rear suspension of Nuna8 has been designed following a similar concept as Nuna7, featuring trailing arms. The advantages of this concept are its relative simplicity and excellent stability, as long as you don’t require the rear wheels to steer. Given the fact that trailing arms have featured in Nuon Solar Team vehicles since 2001, experience with the concept made for an easy decision. “This year we have managed to save weight compared to Nuna7’s rear suspension, as we have designed separate components for Nuna’s right and left rather than just mirroring the design. This allowed us to tailor our design for both sides, rather than overdesigning one of the two” Bart explains.
During the design process already there has been plenty of discussion with ECN (the company producing our mechanical components) about the production of all parts. “It’s not that we hand in our technical drawings and that’s it”, Thijs explains, “the grey area between design and production is also taken into account.” “Whenever problems were encountered, a meeting with ECN always managed to solve our problems”, Bart adds. “ECN has partnered the team for a long time and that shows, as they know very well what is important to the team.” A special tradition within our mechanical department is the mechanics taking a dive in the sea at Petten (next to ECN’s headquarters) after collecting milled components, Thijs and Bart certainly lived up to expectations on this front. “We picked up our first batch of components in February, so the sea was freezing cold!” Thijs jokes.
So far Nuna’s suspension has lived up to the expectations, giving Nuna’s drivers ample feeling during their ride and most importantly giving them the confidence to drive Nuna8 at high speeds. And considering the fact that this suspension will guide Nuna8 past 50m long road trains, that can only be a good thing!