TU Delft Project MARCH team shows improved PCB designs in their Exoskeleton

Project MARCH is the TU Delft dream team which focuses on exoskeleton technology. An exoskeleton is a robotic suit designed to allow people with paraplegia to walk again. We design our exoskeleton in collaboration with someone who has a spinal cord injury, we call this person our pilot. We use our exoskeleton to compete in an obstacle competition for exoskeletons, the Cybathlon. Every year a team of students builds a new exoskeleton, with the exception of our year as the fifth Project MARCH team. We continue with improving the MARCH IV, the fourth exoskeleton, to compete with it in the world championships later in this year.

An exoskeleton is a complicated type of assistive robot which is built from parts that can easily be compared to aspects of the human body. The bones and joints of a human are comparable to the aluminium bones and joints we have in our exoskeleton. We have eight joints in the exoskeleton, one in each ankle, one in each knee and two in the hips. One of the hip joints is for forward movement and one of the joints is for stepping sideways. The joints each contain a motor and the power for these motors is regulated from the battery in the backpack.

The communication between all these parts is done via the electronics in the exoskeleton and in this blog post we would like to share with you some of the improved PCB designs we made for this year.

MARCH IV Team Photo

The Printed Circuit Boards in the exoskeleton

Our exoskeleton contains multiple different Printed Circuit Boards. Below we’ll share the basics with you on these components. These PCB’s were designed last year (read more about these designs here) and our electrical engineers analysed them at the beginning of our team year in September to see where improvements could be made.

The electrical engineers of this year Project MARCH team are introduced in this video

The Power Distribution Board

This is the PCB which converts all of the voltage from the battery to the right voltages for each of our eight motors.

This is our largest PCB in the exoskeleton, although it is only slightly bigger than your average chocolate bar. This is done on purpose as our PDB is located in the backpack, which cannot be any bigger than the back of the pilot.

General Ethercat Slaves PCB’s

Our General Ethercat Slaves (excuse us for the name, we had nothing to do with that) are our sensors and the PCB’s that are connected to the GES’s are the PCB’s where all temperature information on the joints is received.

We measure these temperatures as a safety measure.

We do not want our joints to become too warm, as this might burn our pilot. Since she cannot feel the temperature from our joints (due to her spinal cord injury), we’ve included this safety feature. In our exoskeleton there are five of these PCB’s.

There are two in total in the ankles, then there are two which on each side of the exoskeleton receive information from one knee and one hip and then finally there is only one GES PCB in the backpack which receives information from both a left and right hip joint.

Differential Converters PCB’s

Our differential converters, as can be guessed from the name, convert the signal from each encoder to a differential signal. This is done as a differential signal causes less noise on the data cables and we want to ensure nothing disrupts our data communication.

These eight PCB’s are the smallest PCB’s we have in the exoskeleton and they are only slightly bigger than a large bite from a chocolate bar.

Motor Controllers PCB

For each of our eight motors in the joints we have a separate motor controller, with its own PCB. These PCB’s translate the encoder data we receive into a format that can be understood by the motor controllers.

These PCB’s were redesigned this year and the reason for doing so is further explained below.

The Improved Designs of our PCB’s

Last year during tests with the exoskeletons our team noticed some inconsistent behaviour, with occasionally some errors occurring. We believed this to be partly due to electromagnetic interference in the exoskeleton.

In our suit there are both data cables (Ethercat) and power cables (both a high and low voltage net).

To make the motor controllers PCB’s more electromagnetic compatible our electrical engineer Eva redesigned it so that the data and power traces would be more divided.

As our motor controllers’ PCB’s were designed last year to be as small as possible (80 by 70 mm) each component was placed very close to each other.

This made the process of redesigning the board quite difficult and thus Eva decided to start with a clean slate. By then dividing the board in two sides (a data side and a power side) she ensured that there would be less interference between the two sides.

Additionally, she paid more attention to grounding by creating one interrupted ground plane in the new PCB design. As the low voltage net will be removed from the exoskeleton, the PCB’s now also have the job of converting the high voltage net locally to a low voltage net.

MARCH IV DesignThe MARCH IV design MARCH IVc DesignThe MARCH IVc design

In addition to redesigning the motor controllers PCB’s, Jefta, our other electrical engineer designed a new PCB for in the input device of the exoskeleton.

Our input device is integrated in one of the crutches that our pilot walks with. Within the handle there are several buttons integrated and a small screen where the pilot can see the different walking patterns and select one with the buttons.

During the year the Project MARCH team noticed that replacing a button in the input device was quite a hassle and so Jefta designed a new PCB for the input device. Each button of the input device is now connected to a connector on the PCB, making it easy to replace each button.

Prototype of New Input Device

A prototype of our new input device with the PCB inside

Coming up …

With our new PCB designs in the exoskeleton we are planning to compete in the Cybathlon 2020!

It’s going to be an exciting obstacle race with 17 fierce competitors. Luckily, we have partners like Eurocircuits to help us get there!

Thank You Eurocircuits

We would like to thank Eurocircuits for supporting our team with PCBs which sit in the heart of the MARCH IVc electrical system. They were quick to respond to all our questions and because of their speed we’ll be soon ready to place our new PCB’s in the exoskeleton.

Willemijn Berkhout | Partnerships & Public Relations
T +31 (0)15 278 98 37 | M +31 (0)6 13 88 56 43
Stevinweg 1 | 2628 CN Delft | The Netherlands
willemijn@projectmarch.nl | www.projectmarch.nl

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