Recently the revealing of the concept electric vehicle from Audi, the R8 E-Tron has been covered widely in the news. It was revealed at the recent CES. The most remarkable I found in the R8 E-Tron was that it had 4 motors, one in each wheel. Not only that, the motors are mounted in the wheel, which makes them direct drive!
The Audi R8 E-Tron - With 4 motors, one at each wheel - Link
There are some big advantages to direct drive, for example it gets rid of any losses you could have from gears or other means to transfer the power from the motor to the wheels. Another advantage is the full torque of the motor is available at the wheel.
The first time I personally encountered direct drive was when I was still Dj’ing, the most famous workhorse back then was the Technics 1200, which uses a direct drive platter. Great for Dj’ing because of the torque. Other applications where direct drive has proven to be succesfull is in the windmills, for example Siemens uses the technology to gain more power from the wind and reduce the maintenance costs and downtime. The direct drive systems in windmills are much more reliable than their geared counterparts.
The Siemens windmill - Direct Drive - Link
In the automotive the direct drive motor is also used, but not is not as widely adopted yet. One company I know of manufactures them, called e-Traction and uses them in buses. They also have models for SUV like vehicles, though I’m not aware if they have them installed somewhere yet. The buses do drive around with them, in a hybrid configuration and the clients and passengers of those buses are quite pleased with them. They offer a smooth and silent ride and avoid a lot of gear shifting when compared with the conventional diesel powered buses.
When can we expect the direct drive motors to be available in the vehicles we buy? The Audi R8 E-Tron is still in the concept phase and is not expected before 2012 or so. Having checked the current Tesla Roadster to see how that one was powered, it seems the Tesla also does not use the direct drive option as can be seen from this picture of a Tesla motor getting installed. Currently these motors are quite expensive when compared to their counterparts, which is probably the reason they did not include them in the Tesla. Perhaps when the prices get lower, or when other manufacturers will also design concepts and plans around these direct drive motors. If you look at the BMW Megacity concept it could also contain some in-wheel motors there, so it might be the way the German car manufacturers want to go. It makes sense from an efficiency standpoint as mentioned earlier.
Though still a sketch, those wheels seem promising enough - Link
The problems that the direct drive motor or the in-wheel motor has to overcome in my opinion for a wide spread adoption in the automotive would be the price level and perhaps a new and closer look at the shock absorbers. The in-wheel motor will also have to be accounted for when designing the shock absorbers. Nothing impossible I’d say, so let them come!