An EV made to demonstrate motion control: the mCar …

Monolithic Power Systems wants optical encoders to run for their money. The MPS mCar EV demo showcased motion control and angle position sensors in electronics 2018.

At electronics 2018, there were several automotive-focused demonstrations at the stands, sometimes even displays of luxury F1 cars sponsored by electronics companies. Among them was a unique non-car-focused display – an electric vehicle specifically designed to demonstrate motion control and angle sensors.

Monolithic Power Systems isn’t necessarily the first company that comes to mind when you think of electric vehicles, especially the veritable sea of ​​advertisements for electric vehicles and automotive-related products in electronics or other popular shows. Yet the mCar, the MPS demonstration, was sitting at their booth, an undoubtedly interesting electric vehicle with spinning wheels crawling across the showroom floor.

The free roaming mCar on the MPS demo video.

MPS mechanical engineer and lead designer of the mCar Aaron Quitugua-Flores explains that the mCar is the brainchild of CEO Michael Hsing. Apparently Hsing loves vehicles and determined that a custom EV would attract the attention of MPS. The problem, of course, was that MPS did not have the required machine shop to develop such a project.

So Quitugua-Flores was simply hired to build one.

Over the past year and a half, a team built a mechanical workshop in San José and designed, manufactured and created the electronic integration for the mCar, in partnership with a China-based team that handled the motor control aspects.

The mCar, in general, represents an extremely ambitious project to develop an EV to demonstrate products that do not necessarily have EV in mind.

The mCar making donuts with its tires turned inward in the MPS video

So if MPS isn’t what comes to mind when one thinks of automotive, how does mCar fit into electronics? MPS is no stranger to energy-related components, infotainment systems in the auto industry, but nothing that Quitugua-Flores calls a “macro-scale.”

“We’ve had a number of people ask, I am assuming jokingly, ‘Can we buy the car?'” He says. “And that’s part of the reason we wanted to build something like this. We wanted people who don’t necessarily know what MPS does to be able to come in and start a conversation.”

While MPS is not trying to sell a car, the mCar shows several features that one may need in their own applications. In addition to showing the main components of MPS (power regulators, voltage regulators, voltage converters, etc.), the mCar hopes to demonstrate two main functions:

  • motor control elements
  • angular position sensors

Intelligent motor control modules

The mCar displays various smart motor modules. These include a BLDC motor coupled with an integrated control module already connected to the motor. “With that,” adds Quitugua-Flores, “we have a rotor position sensor and a field-oriented control integrated on the same chip. The associated board, also mounted on the motor, includes motor drivers and a local MCU. The goal is to make application integration very agile. “

An engine control module in the mCar.

The initial developments of the mCar included only magnetic angle detection, but the current iteration shows the integrated magnetic angle detection with the control of brushless DC (BLDC) motors. In essence, it shows the ability to “control everything together” in one package.

Although smart motors are not ready for the automotive space, BLDCs are becoming more dominant in many other applications, such as robotics.

Non-contact magnetic angle sensor

Beyond smart motors, angle detection is what MPS hopes people will remove from the mCar demo, as they are applicable for many systems today.

In mCar, an example is the drive-by-wire features. “In our car,” says Quitugua-Flores, “the steering wheel is completely cable-driven, so there is no mechanical connection between the steering wheel and the actual turning tires. We have a magnetic angle sensor that detects the angle of the steering wheel. and convert that to what the tire angle should be for various steering modes. “

In the image below, an MPS angle sensor, indicated by the blue LED on the right, is mounted directly to the steering column on the other side of the dashboard, detecting when the driver turns the wheel.

From left to right, the steering wheel, instrument panel and angle sensor measure the angle of the steering column.

In this case, the sensor information is sent wirelessly to the rest of the car to tell the wheels to turn, etc. This, Quitugua-Flores says, is a remaining feature of the mCar development where steering commands had to be entered remotely before a driver’s seat was added.

The angle sensor attached to the steering column, together with the plate and the antenna send signals wirelessly to the wheels, etc.

The same rotating magnetic angle sensor is used on both the accelerator and brake pedals, sending data wirelessly or via wired signals. As on the steering wheel, the brake and acceleration pedals are equipped with angle sensors directly at the pivot point to measure the angle at which the pedal is depressed.

An angle sensor seated at the pivot point of the pedals.

“Everyone assumes that, at some point, everything will be wired or wireless, wireless. To some extent, it is like looking to the future,” adds Quitugua-Flores.

But of course, the mCar is not set to revolutionize the EV space just yet. “Since this is an R&D application, we don’t have to immediately think about the NHTSA (National Highway Traffic Safety Administration) type of safety standards.”

Suspension control: angle sensors and engine control

Another aspect of the mCar that isn’t likely to show up in traditional automotive setups, however, is one of the things that Quitugua-Flores thinks makes the demo so cool. The car’s cab / driver seat rotates freely, suspended from the front and rear suspension modules. As Quitugua-Flores explains, the center of gravity is positioned in such a way that when the driver turns a turn, he leans into the curve, essentially like an airplane or motorcycle. “[The driver is] pushed down on the seat instead of pushed sideways out of the seat. ”

The view from under the mCar when the driver’s seat over tilts in a turn. GIF courtesy of Monolithic Power Systems

This is a demonstration of sensors and motor control systems working in tandem.

Quitugua-Flores explains the system like this: “We can connect one of our angle sensors and detect that rotational position. We take that information and send it to our suspension control. We have a design for our shocks with a BLDC motor and our smart El built-in motor there can change the length of each shock absorber and thus change the camber, which is the vertical camber of each wheel. The ideal scenario is that when the frame leans by one turn, the suspension changes in such a way that the tires will also lean in the same direction … In essence, it’s like a four-wheel motorcycle. “

The upper angle sensor is connected directly to the axle that suspends the driver’s cab. This sensor tells the suspension how to behave to allow the driver a smooth ride.

Obviously, this is not something that is part of typical vehicles, but versions of this type do exist in mostly urban concept EVs and even some ATVs.

A battle of precision: magnetic sensors versus optical encoders

The mCar displays some of the sensors and motion control needed to make an EV demo run effectively, but this isn’t necessarily a high-precision application. For systems that require high precision, MPS also has a robotic arm with seven degrees of freedom in the cockpit.

Inside the arm, explained Jake Beahan of Productive Robotics, are 16 MPS angle sensors, each indicated by a blue LED. This demo is to show that precision applications are certainly possible for the current generation of MPS sensors.

The robotic arm spent its time in electronics carefully passing soccer balls from one holder to another to demonstrate precision control.

For higher precision applications, however, MPS will have to improve its game.

The current competition, Quitugua-Flores says, is optical encoders that can achieve the same functionality as these magnetic angle sensors.

“An optical encoder requires a disk and a light source and the disk mounted on whatever rotating element it has. A common example is the shaft of a motor. This disk would be mounted on a rotor shaft and an associated light source would make it shine. a light through the slits. that are cut in the disc. Through different methods of cutting the grooves in the disc … you can get very high precision positional detection. “

Compare this, he says, to MPS’s magnetic solution: “All we need is a simple diametrically magnetized disk that is attached to whatever rotating element you have and then we have an IC – just for our single angle sensor, it’s a single-angle IC. 3mm by 3mm “That is either directly in front of this disk or mounted on the side of that magnetic disk. Therefore, we do not have any contact with the rotating element. “From this perspective, it is a matter of simplification, the difference between” a simple IC “and” a complete optical configuration, which includes the light source, whatever is necessary. to interpret the light, filter the light and then make the puck, depending on the level of precision required. “

MPS’s ability to make an IC, he says, “can also cut costs quite a bit,” which can be a difficult point when comparing these two technologies. “The cost,” he says, “and, to some extent, the complexity to implement [optical encoders] It can be a barrier for some. Using the MPS background and knowledge with ICs… is where we feel we can make a difference. “

The path to more accurate magnetic solutions

To convince customers to replace their optical encoders with magnetic solutions, MPS will need to demonstrate the ability to produce products capable of highly accurate position sensing. The path to these more accurate solutions, Quitugua-Flores says, has a lot to do with data processing and filtering. Essentially, it all comes down to software development.

“With magnetism,” he says, “some of the problems we can have are that the magnet is not perfectly symmetrical or that the mounting of the magnet with respect to the sensor is not ideal. Therefore, we do not have linearities with the magnetic field. . which is the main element that we need to detect the position. Therefore, with our software development, we can overcome those imperfections in the assembly and production of the various components. So that’s one of the things where our team is working right now: how to make processing reliable and effective for precision gains. “

Some of the concepts demonstrated in the mCar have far-reaching potential in the automotive industry. However, their systems have broad relevance to applications being developed today, even when demonstrated in a unique and ambitious way.

What is your impression of the mCar? Have any idea of ​​the comparison between optical encoders and magnetic angle sensors? Share your thoughts in the comments below.