Published: 27.03.09
Citius dossier

What makes a good bobsleigh? Jump in and find out…

The Kinematik I team of the bobsleigh construction project Citius under the direction of ETH Zurich shows why it is important for an engineer to get his hands dirty in the workshop himself if he is to become a bobsleigh builder.

Simone Ulmer
Pascal Arnold undoes some screws in the steering mechanics of the Citius bob. (Photo: Pablo Faccinetto)
Pascal Arnold undoes some screws in the steering mechanics of the Citius bob. (Photo: Pablo Faccinetto) (large view)

While Pascal Arnold undoes four screws in the paneling of the housing of the 2-man Citius bob in the Department of Material Science workshop, which protect the steering mechanics of the Citius bob from spying eyes, Christian Reich works on its brakes. Pascal Arnold is a PhD student at the Institute of Mechanical Systems, and Christian Reich a bobsleigh builder and, until recently, successful bobber himself. Together, they are preparing the newly constructed, as yet unpainted second model of the 2-man bob for the pilot training camp in Cesana, in the Italian province of Turin. It does not matter that the paint is missing; the important thing is that the shell is fit to drive. Arnold is a member of the Kinematik I team headed by Christoph Glocker, Professor at ETH Zurich’s Institute of Mechanical Systems. The team developed and, with the support of its industrial partners, produced the chassis for the Citius bobsleigh.

Pilot school for ETH Zurich engineer

For Pascal Arnold, who is a PhD student under Glocker, the project meant – like for many of those involved – a labor-intensive year, but also a unique, exciting and varied project, especially as the Kinematik I team did not have the faintest idea about bobsleigh building before the official project launch in the fall, 2007. Consequently, they were reliant on the close collaboration with Christian Reich for the construction. They spared no effort themselves to bring in as much sensitivity and experience as possible, however. Arnold even spent a week at a pilot school in St. Moritz learning how to drive a bob and feel what is important for himself. All the other bobsleigh designers went on a so-called taxi ride in a bob to gain an impression of what it means to drive one, just how quickly it moves down the ice track, and the immense forces that come into play. Up to six times the force of gravity is exerted on the pilots on corners like the famous Horseshoe in St. Moritz, for example. That is equivalent to driving around a multi-storey car park full of bends at 100 km/h.

Goal: A sportier sleigh

For the team, the first significant step in developing the chassis was the test runs using an existing bobsleigh, which Christian Reich piloted in St. Moritz in February 2008. Beforehand, the scientists fitted the bob with a transportable measuring instrument they had put together especially, which enabled the team to measure the forces and stress exerted on the bob. The measuring device, which had to withstand the stress, revealed which forces are exerted where on the chassis, what kind of vibrations occur, what the spring deflection is like in different parts of the bob, and how rigid the chassis is. In analyzing the data, the team soon discovered details which needed improving if they were to make the sleigh sportier – Arnold’s stated aim.

The team spent almost a year perfecting the concept for the chassis, reconstructing and recovering every part of it. Strict regulations did not leave much room for maneuver. “In this connection, it was not only crucial for us to hit the drawing board but also get our hands dirty down in the workshop,” explains Arnold. That is the only way to really see what matters.

A chassis that launched a thousand pieces

During the construction, the team soon realized that their computer designs and the actual execution were poles apart. From the most sensible work sequence and the production technique to the search for materials: The entire construction was up to ETH Zurich, namely Pascal Arnold and his colleague Martin Elsener from the Department of Material Science workshop. Of the 1000 special parts in the chassis, 200 components were developed at ETH Zurich using the CAD. The company V-Zug produced the bulky components, Schörling was responsible for the small parts and the steering, and Promtec Estech the welding work.

The moment of truth came at the beginning of February: Citius had to pass its first test run at the bobsleigh track in Igls (see ETH Life article from 19.12.2008. It was fitted with the same measuring equipment as the test sleigh one year previously. They now had to compete against each other. The results, like those in the wind tunnel (see ETH Life from 16.12.2008), were more than satisfactory. Nevertheless, we can only speculate as to what impact the improvements will ultimately have in a real race situation and whether the sleigh really is faster. Glocker says: “The time the improvement of the chassis saves is very indirect.” After all, a better chassis primarily only makes a vehicle easier to steer, making the driver less likely to make mistakes and thus gain time.

In the coming weeks, there will be test runs for the pilots, during or after which they can suggest further improvements. However, the trial runs conducted so far have shown that the athletes are generally very happy with the Citius bob. The steering apparently takes some getting used to and differs considerably from the traditional one in terms of the construction – that is why their mechanics are also covered and had to be exposed by Pascal Arnold’s screwdriver first to offer a glimpse of them.

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