PCB design for motorcontroller
Here Michael again from project march, I will tell you something about our PCB design process for the motorcontrollers.
For our exoskeleton to walk, each joint is actuated by a motor. We use 2 different motors, for the hip and knee joint a brushless DC motor with 21 pole pairs from tiger motors. And for the ankle a brushless DC motor with 7 pole pairs from hacker motors is used. These motors are all 3 phase motors and need a special controller to let them rotate.
These so called motor controllers operate by applying a PWM signal to the 3 phases of the motor, simulating a sinus with a 120° phase shift. This so the coils are attracted and pushed off the poles at the right time.
In our exoskeleton we use the iMOTIONCUBE from Technosoft. As you can see in de picture it is really small, but it can power motors up to 1kW. We don't need his amount of power, but we do need relatively high currents, up to 30A for the motors.
For the controller to work we have to add some extra components for the sensors, also it is kind of hard to connect the sensors, motor and power to the controller. For these reasons we designed a PCB with these components and connectors for easy connections and disconnections.
For our PCB designs we use the program Altium Designer, where we first draw the schematics. Since a big part of the the PCB is a break out for the iMOTIONCUBE to connectors, the schematics are not difficult.
After this the hard part came, which was placing all the components and connectors within a given boundary given by the frame department. As you can see in the pictures below, there isn't any room for a bigger PCB, taking into account the connectors and bending radius of the cables.
Eventually it came down to moving connectors 0.5 mm to make everything fit and have the right clearance. Then it was time to place the power traces or the input and motor outputs, which are rated for 30A. With the space we had and clearance needed, we decided to add extra layers (8 layers) to achieve this requirement. This made routing the sensor signals relatively easy, since now there was more then enough space.
After all the routing was finished and checked by our partner Sintecs, who helps us by our PCB designs, we send the design to the manufacturing and waited untill:
Now we could test it and except for 2 small fixable mistakes it all works and we can rotate our joints, to see the result keep an eye out on our social media.
Thanks for reading, in my next blog I will tell something more about the sensor for the motor commutation.