Capturing Action Films with High-Power Servo Drives

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Computer-generated imagery (CGI) can create incredible scenes in cinema, but often, live-action shooting can be more visually exciting. However, human-operated dollies can't always keep up with the speed or acceleration needed. Therefore, Mega Trax created the MX 500, which is a high-speed, semi-autonomous robotic dolly system. Using Elmo Motion Control's high-power, compact servo drives, the MX 500 can accelerate cameras to over 90 mph in a few seconds.

The Mega Trax design team encountered challenges at every turn when building the MX 500, beginning with the payload. The range of cameras utilized for feature films can weigh almost 100 pounds. They move down a rail system on a cart referred to as a dolly, which can also weigh several hundred pounds.

The motion must be quick, seamless, and repeatable to allow the director to shoot the scene several times where required. The team could have chosen to establish the system by using a single motor, fixed to the wheels with gearing and couplings. However, this would have added backlash and compliance that may have compromised the quality of motion.

Rather, the team selected a dedicated, high-power servo motor to power every wheel of the MX 500 dolly cart. The problem was in discovering a motor-drive solution that could provide not only explosive acceleration, but also make sure that the four motor drives had a tightly synchronized operation to stop any instability from materializing in the shot.

With travel distances that can be up to several hundred feet, the MX 500 needed to be a portable device. That introduced all of the problems encountered when using portable applications. The drives had to be compact and light enough, while still offering enough power to energize the motors.

They also had to be efficient enough to provide adequate battery lifetime. A robotic dolly cannot be of true assistance if filming is frequently stopped to charge its batteries. A critical need for the MX 500 was also to make it simple to use and quick to program.

GOLD DRUM HIGH VOLTAGE (HV) Super compact, Direct-to-mains, EtherCAT/CANopen servo drive (up to 65kW)

GOLD DRUM HIGH VOLTAGE (HV) Super compact, Direct-to-mains, EtherCAT/CANopen servo drive (up to 65kW)

Filmmakers work with strict budgets and even stricter schedules for shooting. When filming outdoor shots, they are also impacted by the weather and light conditions. Producers and directors were unlikely to adapt to a system that required extra training or a large amount of programming time before each new shot.

The Mega Trax team was searching for a user interface that would be simple to customize and train. Lastly, the solution needed to be hardy enough to cope with the environment of outdoor filming. Location conditions can be more extreme than those presented by industrial applications.

Equipment must pull through exposure to dust and dirt, temperature extremes, shock, vibration, moisture, and much more. Film crews need to be able to trust the equipment to carry out the shot each time. This means that they also need to be able to trust the performance of the drives.

When the design team at Mega Trax were searching for a drive that could perform the job, they discovered it with the Gold Drum HV servo drives from Elmo Motion Control.

Elmo has a great reputation for precision motion control, so we already had a high level of confidence in the company," explains Howard McCain, co founder and CEO of Mega Trax. “Then, we realized that Elmo’s drives were the only ones that could handle our power and motion control requirements.

Lightweight, Powerful and Connected

Every Gold Drum HV servo drive can operate up to 100 A or 800 V and can deliver over 65 kW of continuous output. A major benefit of the drives is that they are designed for high power density, which allows them to provide that output power in a compact, lightweight form factor, well adapted to applications that require portability.

Gold-Drum drives also have an efficiency rate of up to 99%. Due to this, the MX 500 is capable of performing up to 50 high-speed, quarter-mile runs per charge of the system’s dual 800 V batteries.

It is not just the quantity of motion, but also the quality of motion that is important. The system needed a highly synchronized operation of all four axes with the least possible downtime to ensure the cart moved smoothly. The team was able to do this by utilizing the drives’ built-in connectivity and intelligence.

The four drives on the wheels of the dolly cart are fixed together in a master-slave architecture utilizing EtherCAT and CANopen. They operate in torque-follower mode, with the master drive giving commands to the slave drives.

Along with the hardware of the drive, The Mega Trax team used the Elmo Application Studio II (EASII) motion design software to design a versatile and user-friendly programming environment for the MX 500.

EASII allows users to efficiently create and implement motion, and intuitively program and control Elmo’s servo drives. Remote connectivity using a mobile device attached to the robotic dolly made it a possibility for Elmo technicians to optimize performance by tuning the drives when the system was on the track.

I loved the online tool that provides EASII software training with a live video link to a real machine—it allowed me to personally perform a quick tune on our motors to get everything rolling,” describes David Kuklish, Co-founder and VFX Supervisor, Mega Trax.

The EASII motion design software tool also enables precise mechanical plant transfer functions; 1D, 2-D, and 3D corrections and error mapping; drive feedback emulation; corrective servo tuning capabilities and features to optimize the performance of the application.

This information has been sourced, reviewed and adapted from materials provided by Elmo Motion Control Ltd.

For more information on this source, please visit Elmo Motion Control Ltd.

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