BCN 3D Motor Driver Setup and Current Limit Modification
The BCN 3D requires multiple motor drivers connected to the microcontroller. This setup looks complicated to the beginner’s eye, but is laid out neatly using Fritzing software. The two necessary steps for this subproject: interpreting and using the Fritzing diagram provided (recommended: start by creating an initial Fritzing diagram to understand the software. The learning guide is provided online [3]).
Figure 1: Fritzing Diagram for the DRV 8825 Pololu motor drivers, the power supply, a capacitor, and Arduino microcontroller.
Figure 2: Setup for an individual motor driver and Arduino Mega.
To start, prepare two power rails, one 5V and the one 24V. The right power rail in this image, Figure 2, is the 24V power rail and the left one is the 5V power rail.
After all the motor drivers have been set up as in Figure 2, review the tutorial video for how to set the current limit on each DRV 8825. There are additional resources for this provided by Pololu, on their documentation [2] and on their YouTube channel [4].
Figure 3: Student tutorial on current limiting.
Figure 4: The final result, with extra capacitors added (one per motor driver).
The final result is seen in Figure 4. As a personal experiment, research what is a capacitor and why they are necessary components for the circuit. Note that Pololu provides the following information [2]:
“Warning: This carrier board uses low-ESR ceramic capacitors, which makes it susceptible to destructive LC voltage spikes, especially when using power leads longer than a few inches. Under the right conditions, these spikes can exceed the 45 V maximum voltage rating for the DRV8825 and permanently damage the board, even when the motor supply voltage is as low as 12 V. One way to protect the driver from such spikes is to put a large (at least 47 µF) electrolytic capacitor across motor power (VMOT) and ground somewhere close to the board.”
References
[1] Brain, Marshall & Pollette, Chris (2021). How Capacitors Work. How Stuff Works. https://electronics.howstuffworks.com/capacitor.htm
[2] DRV8825 Stepper Motor Driver Carrier, High Current. Pololu. https://www.pololu.com/product/2133
[3] Getting Started. Fritzing, Electronics Made Easy. https://fritzing.org/learning/
[4] Pololu Robotics and Electronics (2015). Setting the Current Limit on Pololu Stepper Motor Driver Carrier. Pololu. https://youtu.be/89BHS9hfSUk
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