Even now in the 21st century, a person with a spinal cord injury is in a wheelchair for the rest of his/her life. Project MARCH would like to change that. We believe that technology can improve the quality of life of people with spinal cord injuries. We do this by designing and building a prototype exoskeleton each year for our pilot Koen, who was diagnosed with a Spinal Cord Injury eight years ago. An exoskeleton is a motorized robotic suit which allows people with paraplegia to stand and walk again. The team consists of 26 students with various backgrounds who put their study on hold for a whole year to work on the project.
This year we wanted to take a big step in the exoskeleton technology. We aimed to make our exoskeleton ready for daily use. Our goal was to be able to walk around the city center of Delft in August and we are happy to say that we achieved this goal.
We made this happen by making sure the Project March exoskeleton could walk dynamically. This means with the use of depth cameras. These can be seen as the eyes of our exoskeleton, the MARCH VI. One depth camera is aimed to the front and one to the back. The one to the front scans the surroundings of the exoskeleton thus adapting the step size of the exoskeleton so that every kind of stairs, ramp or curb can be overcome. The depth camera in the back is for scanning the height of different kind of bench so that our pilot and the MARCH VI can sit everywhere!
This year we as electrical engineers of Project March mainly focused on the development of two printed circuit boards.
One of them is the Power Distribution Board (PDB). As the name suggests the PDB is responsible for distributing the power, which is supplied by the battery, to all the electrical components inside the exoskeleton in a safe manner. Since not all components need the same voltage the PDB contains several power converters to convert the 48V delivered by the battery to 12V, 5V and 3.3V.
The 48V which is supplied by our battery is called the high voltage. This is used to power the motor controllers. In previous years we used the IMotioncubes as motor controllers. For each joint in our exoskeleton an IMotioncube was needed. However, this year we switched to the ODrive as motor controller. The advantage of the ODrive is that one ODrive can control two joints. This means that less high voltage connectors are needed which means the PDB could be smaller this year. Since the space in the backpack is very limited this is a huge advantage.
Another change in our exoskelet is the new and more powerful master computer. The master is a single board computer that acts as the brain of our exoskeleton. Since this new master is more powerful it consumes more power. Therefore, the dc converter, which converts the 48V from the battery to the 12V the master needs, had to be changed. Furthermore, the larger power consumption of the new master means that more heat will be generated inside the backpack. Therefore, more connectors are added for fans to compensate for this increase in heat generation.
The last important change we made is the added connection with the battery management system (BMS). The BMS is a small PCB which is placed on the battery and checks the status of the individual battery cells. In previous years the data collected by the BMS could not be stored anywhere. This means that we had no real data about the power consumption of our exoskeleton. To get more insight in our power consumption we added an extra connector on the PDB. By doing this, the data can be sent from the BMS to the PDB using UART, which is a communication protocol. Since the PDB is connected to the master computer, the data can thereafter be logged.
The other PCB we designed this year is the Dieboslave. This is a communication board which will be attached on top of our new motor controller, the Odrive. In our exoskeleton we use the ethercat protocol to communicate between the different components. However, the new motor controllers are unable to use ethercat. Therefore, a separate board is needed to convert the UART signals the Odrive uses to Ethercat signals.
Another function of the Dieboslave is to add more reliable connectors for the encoders. Since the Odrive only has only one SPI connector slot and we need two of them for the absolute encoders. Furthermore, the connectors present on the Odrive are not very sturdy and we feared for easily disconnected cables. Therefore, we added more reliable connectors on the Dieboslave.
These PCBs were designed using Altium. Thereafter, the designs were sent to Eurocircuits who reviewed and fabricated them.
The Project March Team wants to thank Eurocircuits for their support in our project.