High Power Density Drives Propel Soft Target for ADASs Testing

Elmo’s servo drives are helping AB Dynamic build high-power, low-profile Advanced Driver Assistance Systems (ADAS) testing platforms. That’s no simple task when you consider that the platform must move at highway speeds on very small wheels, and be able to turn at a complete stop, despite the high friction. Read the full story here.

Read this case study to learn about

  • Using high power-density servo drives to deliver high power in a small package
  • Utilizing a built-in phase advance algorithm to surpass RPM ratings, with negligible impact on motor efficiency.
  • Designing highly reliable products that can operate under extreme conditions.
High Power Density Drives Propel Soft Target for ADASs Testing


Advanced driver assistance systems (ADAS) such as anti-collision systems, lane-departure warning systems, and adaptive cruise control constitute a rapidly growing segment of the automotive market.

To help developers test their systems without damaging the vehicles involved, AB Dynamics has developed the Guided Soft Target (GST). The GST consists of a disposable vehicle mockup (the Soft Car 360) mounted on an autonomous robotic platform. The autonomous robot needs to propel the soft shell at highway speeds while preserving a low enough profile so that a direct collision with the test car will not damage that vehicle’s wheels or suspension.

During testing, the GST platform carries the Soft Car 360 down the test track, following a preprogrammed sequence of movements. If the test vehicle collides with the GST, only the mockup is damaged.

Machine requirements

The autonomous robotic platform must be capable of high speeds while providing precise, accurate steering that enables it to repeat test sequences exactly. To minimize cost, complexity, and part count, AB Dynamics designed the platform with two passive steering wheels in the front and a single active drive wheel in the back. The limited space underneath the low-profile platform, which is just 12.5 cm high, needed to accommodate wheels, motors, gearboxes, and drives, so every component needed to be as compact as possible.

“When we reached out to Elmo, we had some very specific requirements in terms of form factor, power density, and reliability,” says Matthew Hubbard, chief operations officer at AB Dynamics. “They worked with us to deliver exactly what we needed.”

Motion control solution

The drive-wheel assembly consists of a single DC servo motor operated by two Gold Drum servo drives. Each delivers 100 A of output in a package that is just 75 mm tall, making it a good fit for the application both figuratively and literally.

The smaller the wheel diameter, the faster it needs to turn to achieve highway speeds. Elmo drives apply a technique known as phase advance to enable motors to safely operate at speeds several times faster than rated. The trade-off for phase-advance mode is a slight drop in efficiency, but, as the drives are already 99.6% efficient, this does not markedly impact the application.

With the Soft Car 360’s large cross-section, air resistance is a factor. Countering the resistance requires high torque from the motor. Elmo drives deliver higher power densities, enabling the drives to fit in the limited envelope available underneath the platform while still providing the required high voltage torque.

High torque was also required for the steered wheels, which need to change angle rapidly and accurately when the vehicle is at a stop and friction is at its most extreme. Searching for a servo drive with the highest possible power density, AB Dynamics chose an Elmo Gold Trombone servo drive to power the steering motor.

Crash tests are run outdoors and in quick succession. This means the GST needs to operate reliably and in conditions that replicate real road conditions, including extreme temperatures, high shock and vibration, and contamination by moisture, dust, salt and snow melt. The high-efficiency Elmo servo drives enable the target vehicle to be operated all day on a single battery charge. In extensive testing, the Elmo drives survived prolonged exposure to track conditions without any issues.


“We have adopted Elmo motor drives across our track testing products, and they have proved to be extremely reliable,” says Hubbard. The company is working on a new version of the GST that provides even better performance, partnering once again with Elmo. “We’re currently working on a new product that is only feasible due to the availability of Elmo’s Gold Twitter drive, which has unparalleled power density,” he adds.

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