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Bravado - Small AWD Off-Road Truck
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| Bravado scale model |
| 20-Dec-2002 12:00 |
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| Bravado digital model |
| 20-Dec-2002 12:00 |
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| Bravado equiped with a sand tray |
| 20-Dec-2002 12:00 |
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| Bravado AWD option |
| 20-Dec-2002 12:00 |
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| Bravado tank truck |
| 20-Dec-2002 12:00 |
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| Bravado suspension travel |
| 20-Dec-2002 12:00 |
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| Nastran analysis of the Bravado chassis |
| 20-Dec-2002 12:00 |
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| Bravado AutoCAD 2002 model |
| 20-Dec-2002 12:00 |
Bravado was a small AWD truck designed to be used in the difficult terrain found in construction sites. High manoeuverability and small size were its main features. As a friend of Fulvio and future engineer student, I followed this project closely. This article shows the motivation for its development and some of its technical aspects.
It started in 2002. It is only on the final year that the Mechanical Engineering course at FEI focuses entirely on Automotive Mechanical Engineering. The beginning of the final year also marks the beginning of the development of the graduation project, which must be a car, truck, motorbike or tractor for the Automotive Engineering students. The project is presented at the end of the year at the traditional Expo MecAut, to an audience of automotive industry directors, managers and engineers. The expo has a winner, chosen by the audience and the university professors, and the three best projects take a nice trophy home. Of course Fulvio wanted to win.
By March 2002, Fulvio was teamed up with the four colleagues that not only had the highest grades the previous year but also carried a very good grasp of the real world of Mechanical Engineering. Ricardo Guerlenda and Ciro Stefani with great theoretical knowledge, Rodolfo Mantovani with his mechanics experience, and Renato de Biaze always with new ideas of how to solve problems, led by Vehicle Dynamics and Transmission Professor Celso Argachoy. The team initial desire was to create a smaller version of the Baja class 1-1600 car: a simple and very light open-wheeler with a big mid mounted air cooled motorcycle engine. The project was codenamed Electric Chair, since it had little or no regard to safety.
"You are not going to win, your project is not marketable.", the professors used to say. Fulvio was decided to change this with a good marketing plan aiming at the rally and motorcycle enthusiasts like Mantovani, Stefani and Biaze, dirt trail riders. But after 3 months of development, the professors' speech got a little more intimidating: "You are not going to pass, your project is too simple." Arguing the project was as simple as Colin Chapman's designs did not help at all. By late May 2002 the Electric Chair was abandoned.
3 months behind the rest of the class, Fulvio needed a new project. My brainstorm sessions with Fulvio always ended up on race cars, which by expo rules would never win the competition - otherwise all projects would be race cars. It was still May when Professor Ricardo Bock suggested a project taken to the university by a businessman. The project consisted in a small truck for construction sites. Hesitantly, Fulvio and his team took the project. The businessman's concept was a 6-wheeler with an expensive all-independent suspension and chain transmission to 4 of the wheels. And he claimed market for it, given he could develop the project with the university.
There was no engineering requirement for 6 wheels nor independend suspension, and the chain transmission was deemed not to work. In fact, the 6 wheels would create so much drag that the small vehicle would not steer properly. Not able to change his mind, Fulvio's partnership with the businessman lasted only for a month. But the team was keen on working on the project now codenamed Bravado - name suggested by Guerlenda after this.
The technical paradox of the Bravado was to use the Volkswagen air cooled powertrain mounted transversely so to use a slightly modified VW gearbox as the longitudinal differential. This is not a new and it had been used by AWD enthusiasts for at least 20 years, but it is not common to see such a choice hit production for packaging difficulties, noise, and emissions. The VW powertrain was selected for its price, availability and simplicity, while noise and emissions would not be an issue on the Brazilian civil engineering market. The longitudinal differential also provided extra reduction, necessary for traction and to keep the final speed down without requiring further changes to the gearbox. Dana limited-slip transversal differentials distributed power to the wheels. The engine selected was not taken from the Beetle, but a lower profile version of the same engine used on the Volkswagen Brasilia so to fit under the tray. Fuel options were ethanol and natural gas, both popular options in the Brazilian market.
A very strong value analysis was applied to the Bravado, and simple elements were used wherever possible. It was, still, a truck put together as a collection of aftermarket parts. The front suspension geometry was borrowed from the Beetle with the necessary adjustments to increase the travel required on off-road applications, therefore bigger. Most of the steering system was taken from the VW Beetle with some small adjustments. Standard wheels, tyres, headlights, brakelights and seats helped keeping the costs down. The rear truck-like suspension had the springs acting as sole structural elements. The convoluted chassis was actually required to keep the weight to a minimum while linking and holding together all elements of the car, staying away from the axles and suspension.
The team made extensive use of AutoCAD and MSC/Nastran, simulations and spreadsheets. Fulvio developed 116 different chassis designs for the team to chose the lightest and strongest. An AutoCAD digital mockup ensured the layout and spreadsheets predicted the dynamics of the car, the behaviour of the transmission, the engine capacity, and others, as well as dimensioning components. Simulation software was used to dimension the brakes and predict acceleration, maximum speed and load capacity. The final project could carry 700 kg on various tray options, reach 66 km/h, climb a 73% slope and make a complete turn within 12.4 m.
So by December 2002, the Bravado was ready for the 30th Expo MecAut. A scale model was built by Mantovani and a stand was organized with printed information and banners on the project development so the automobile industry guests could evaluate the project. Mantovani answered questions on the model, terrain, and usage, while Fulvio handled the chassis, dynamics, suspension and most powertrain questions. The project was one of the favourites to win so the presentation was scheduled for last. Fulvio presented the project to an university gymnasium full of engineers, managers and directors. Stepping up the stage with the ego of a race car driver who had recently won a championship, he finished the presentation within the scheduled 5 minutes and opened for a Q+A. Very few questions were asked, with most questions concerning the packaging of the natural gas tank while Fulvio was clearly hoping for questions on the dynamics or suspension.
After the votes were counted, Bravado was third place out of seven projects. And yes, the Bravado team got a trophy. Fulvio still has most of the project, and I still have the final presentation here. Some of the CAD drawings have been lost after 7 years. The spreadsheets for the layout, dynamics, powertrain, chassis and suspension analysis and dimension are still well kept with several backup copies, used again by Fulvio on the race track and other engineering projects like the Rodan Electric and the Orion GT. Nice projects, but these will be covered by other articles.
