Good Vibrations

Tesla Motors, Senior Director of Engineering, 13 de dezembro de 2006

Imagine yourself strapped into a Tesla Roadster speeding down a rough cobblestone path intended to cause so much agitation that the ride stops being fun and starts becoming more like work. It's just a typical day at the Motor Industry Research Association (MIRA), an engineering and testing facility where we are punishing two of our Tesla Roadster Engineering Prototypes (and several of our engineers as well!).

All the jostling about is part of a variety of tests we've been performing to ensure the safety, reliability, and durability of the Tesla Roadster. MIRA, a facility built on an old World War II air base in the United Kingdom, is conducting the Pavé and Durability portion of those tests. (We have more cars at facilities in Europe involved in crash testing and other destructive assessments.)

'Peeing man' Rides shotgun in the Pavé Test

The Pavé Test has been designed to put the car through a planned series of shake and vibe elements on a cobbled track. The word Pavé is actually shortened from "Belgian Pavé," and is a copy of medieval European road surfaces, the worst type anyone could find! It's severe: MIRA drivers are only allowed to stay on the track for an hour at a time. The Pavé Test stresses the shock absorbers as well as the driver. Since the goal is to test more than just the shock absorbers, some effort is put into helping them last through the course. The solution is somewhat Rube Goldberg/Heath Robinson, but it works. A large person-shaped water bag is placed in the passenger seat. Tubes lead from the bag to the shock absorbers and water seeps out at a controlled rate to keep them cool. Known as the "peeing man" by the engineers, it is hard to think of a better solution. Actually, after that, it is just hard to think. The surface of the track may appear somewhat random, but it has been profiled in detail. Anytime it is resurfaced, the same dips and bumps are created. This gives manufacturers a perfectly repeatable test, and also allows for an accurate simulation in the workshop. The only weather that will stop a Pavé Test is snow as it fills in the cobbles and results in too smooth a surface. The car will run 1,000 miles of Pavé, taking typically four weeks to complete.

Tesla Roadster climbs 'the ladder'

MIRA also is putting a car through a 25,000 mile Durability Test so harsh it is equivalent to 100,000 miles of normal road driving. This test has many modes, designed to check all aspects of the car and its performance. It includes sections of "lumpy" track – technically ladder racks, corrugations, chuck holes, and more Pavé – as well as a ride and handling circuit and a simulated urban drive (complete with stops and starts). And because we expect our customers to drive our cars fast (we do call it a sports car, after all), we throw in sections of high speed driving into the mix. The picture to the left shows the "ladder." Look closely, there are two possible tracks, one with the ladder rungs in phase and one out of phase. (Click the image to see a larger view of the car on the out-of-phase track.) The out-of-phase ladder is the most challenging for the driver, who gets thrown and pitched in all directions. One of our engineers experienced this ride first-hand recently. (He sat in the passenger seat – the "peeing man" wasn't present.) He said the car did fine, but he did not fare as well. All the teeth-rattling jolts may have loosened some of his fillings! There are a number of other tests that make for an exciting ride - the salt splash, the steep inclines, and the loose gravel. All of these check different aspects of the car and ensure that the pride and joy of our customers can survive the odd "whoops" moment without an expensive repair bill. The handbrake and hill starting capability is tested on a 33 percent incline – especially important to San Francisco residents. The Tesla Roadster passed with flying colors, even earning praise from the drivers. In fact, the Tesla Roadster is particularly easy to start on a hill because there’s no clutch and the motor characteristics make it so straightforward. The horn gets tested too. Since the Tesla Roadster can fly around the track rather quietly, the horn becomes an essential function. Frequently, birds and small animals need to be cleared from the track during the high speed tests with a few quick blasts.

Salt splash

The environmental tests are quite something. They require a driver to sit in a completely sealed car for more than an hour at a time in somewhat less than comfortable circumstances. More on this in a future article, but here is a quick summary.

In the first test, the car is chilled overnight to bring the ambient temperature down to -20°C (-4°F). In the morning, a volunteer sits in the driver's seat and the window (lowered slightly to allow the monitoring cables into the car) is sealed with tape to prevent drafts. The car heater is switched on and much monitoring is done to assess the power and speed of the heater. In a second test, the ambient temperature is taken up to 40°C (104°F). The temperature is raised with an exterior heater as well as simulated sunlight. Once again the volunteer takes to the driver's seat, sealed in to keep those pesky drafts out. The temperature in the car is rather warmer than ambient, especially at head level. The air conditioning is switched on and the driver sits there, monitoring and sweating, as it cools to 30°C (86°F).

Steady acceleration on an incline

The drivers at MIRA work eight hour shifts, five days per week. Apparently, there are enough high points to make all that sweating and shaking worthwhile. The drivers tell us they like driving the Tesla Roadster, and since they get to drive many different types of cars, this is quite a compliment. A team of engineers in our UK office oversees all the tests at MIRA as well as at other facilities. All these tests give us a much better understanding of how the cars will behave during hard and sustained driving over wicked surfaces. The next prototypes we plan to build contain many improvements thanks to the beating we've given our current models.