Control and Expansion Hub Tips

Started in the 2023-2024 season, Tech Tips are segments released in the FIRST Tech Challenge Team E-mail Blast. Sometimes the Tech Tips are included in whole in the email blast, but sometimes there is more content than is reasonable in the email blast so partial content is included in the blast with the rest of the content here.

Port and Wiring Tips

This Tech Tip provides useful tips when using Control and Expansion Hubs.

  • The RS485 data cable ports that provide data between Control and Expansion Hubs are redundant - you can use two data cables utilizing both ports to ensure that if one cable fails communications aren’t lost.

  • Encoder ports 0 and 3 are hardware-counted, but ports 1 and 2 are software-counted. This means higher counts-per-revolution encoders (like the REV Through-Bore Encoder) should be placed on Ports 0 or 3 to ensure counts aren’t missed, and lower counts-per-revolution encoders (like the goBILDA Odometry Pods or most motors) can be connected to any port.

  • Servo port pairs (0,1), (2, 3), and (4,5) each share a common power supply, so if you’re using higher-current servos (like a goBILDA torque servo) directly on the Control or Expansion Hub you should only use ports (0, 2, 4) or (1, 3, 5) in order to maximize the power available to each servo. If you need to use more than 3 high-current servos per hub, consider using a REV Servo Power Module.

  • Each Digital and Analog sensor connector on the Control and Expansion Hub each have 2 signal channels. Some REV sensors are only designed to be configured and used on the N or N+1 channels. Read the documentation for each sensor carefully!

  • The USB 2.0 port shares the same USB bus as the internal Control Hub radio. ESD or other electrical interference that affects devices (like webcams) plugged into that port may cause a loss of communications. When using a USB webcam, use the USB 3.0 port first.

  • USB C-to-C cables do not work properly with the Control Hub, only USB A-to-C cables do.

  • If you’re utilizing the onboard IMU, Do not plug I2C devices into Port 0 unless absolutely necessary. Port 0 shares an I2C bus with the IMU, and misbehaving devices (or devices that don’t “play well with others”) plugged into Port 0 can cause the IMU to stop communicating.

Hardware Connection Diagrams

Have you ever asked, “How does that get connected?” when working with FIRST Tech Challenge control system components? Stefen Acepcion of FIRST Robotics Competition Team 3161 has graciously compiled several connection diagrams that demonstrate different ways that common components can be connected within the FIRST Tech Challenge control system. Driver Station connection diagrams and Robot Controller connection diagrams can be found on ftc-docs. Stefen has contributed additional diagrams, including an Advanced REV Control Hub connection diagram and an Advanced Smartphone connection diagram. These diagrams are chock full of helpful tips, connection techniques, and information you otherwise can’t find in one place - check them out!

Got any questions about the Control and Expansion Hubs? Come start or join the conversation on the FTC Community Forums!