Team 6220 talks new REV Robotics Expansion Hub and plans for next season

Team 6220 Centripetal is part of Swerve Robotics club from Woodinville, WA . This season, Team 6220 had a unique opportunity to assist the FIRST Tech Challenge with testing and roll-out of a newly approved electronics module. Read on to learn about their experiences with the new REV Robotics Expansion Hub.

Q: Tell us a little bit about Team 6220 Centripetal.  How long have you been participating in the FIRST Tech Challenge?  Who are the members and mentors that make up the team?

A: 6220 has been in FIRST Tech Challenge for 5 seasons, but our current team make-up has been together for 2 years. We have 8 students, a coach/hardware mentor, and an assistant coach/software mentor. Our coach is Dr. Fraser, and our Assistant Coach is Dr. Geffner.

As for students, our team captain this year was Jarrod, who put a lot of time into team management. Our systems engineer was Miyu, who did a lot of our CAD and notebook, and who also made a VR simulator of the game in Blender. Our hardware lead was Kirk, who loves having fun with the team and wearing his �schnazzy� pink-sequined suit in the pit. On our software team, we have Mridula, who has been in Swerve for a long time and is involved in a lot besides FIRST Tech Challenge to stay active in the community. Also on software is Cole, who keeps plugging away at the program and has helped bring us together in the past by hosting a Magic draft for the team. In addition, Nikolai is a great designer and builder on hardware who loves the competition for the awesome engineering. Finally, we have our newest member, Kyrie, who has been working hard to learn about the intricacies of FIRST Tech Challenge and its culture. Overall, I guess we can be summed up as a varied group of ebullient pink people!

Q: Team 6220 did some early and more recent work to help FIRST test the newly approved REV Robotics Expansion Hub.  Could you share some of your experiences about the testing?  

A: Well, Swerve Robotics (which is made up of FIRST Tech Challenge teams 417, 6220, and 8923)  helped to test the modules as a whole last Fall, which was fortunate, since there were some issues with getting the v1 and v2 Hubs to work daisy-chained on our team�s Res-Q robot. The tests included driving in straight lines for speed and position accuracy, full power acceleration, and testing of servos, I2C connectivity, DIO ports, and Analog ports for comparable functionality to the previously legal hardware, and performing the hanging maneuver to check absolute maximum motor power.

6220�s robot was the only one that could not perform most of the desired tests with only one Hub. As a result, most of the original tests were run by our sister teams 417 and 8923, which involved exercises to test the robots performing their various tasks from last year and seeing how the modules affected performance. Although we didn�t get to run the tests, we still outfitted last year�s robot (Dupupod) with the electronics and found wire management a lot easier with the new Hubs, with everything running to one spot. However, the earlier models did require a substantial quantity of duct tape to help fasten the 3d-printed bottoms on (no longer an issue, fortunately!). Some feedback was given about orientation and position of the connector sockets, spacing of mounting holes, and number of servo ports, which was incorporated into later revisions, and servo power supply voltage which was not incorporated.

Q: Team 6220 also retrofitted this past season's Velocity Vortex robot with two production REV Robotics Expansion Hubs.  What was your experience performing this retrofit?

A: The retrofit of Quintus Leaf Ericksson (Velocity Vortex robot) went very smoothly, with the only major issue being the creation of cables using level shifters (which won�t be a problem for teams in the next season, as the cables will be sold). Our robot only made it to interleagues, so it was still functionally somewhat sparse.  It did use an omni-drive with vertically mounted AndyMark motors driving the wheels through bevel gears, a rubber-cord flail collector with a CR servo-driven zip-tie paddle wheel to help direct the particles, and a gravity-fed track to our launcher. We had a servo gate to prevent particle spillage and a worm-gear driven �choo-choo� mechanism catapult launcher; the catapult utilized a horizontal piece of saw blade for the spring arm and a touch sensor to detect when it was in a cocked position. We used an I2C connected IMU.

All the functionality worked, although the MR touch sensor did not give an appropriate digital signal level for the REV Robotics Expansion Hub�s digital inputs, so we ran it with an analog port. The choo-choo mechanism jerked the motor shaft when it fired, causing the original MR motor controllers encoder to lose counts, so the touch sensor was mandatory for repeatable firing. We never checked if it could have been omitted with the REV Robotics Expansion Hubs. Driving with the new motor controllers was deemed just as powerful and probably smoother than the originals. The sound of the motors with the new controllers is very cool, as they have a distinct hum that rises in pitch as the motor speeds up. We were disappointed that the servo controllers provide only 5 Volts instead of the normal 6. This reduces torque and speed by ~16 2/3 %, and power by ~31%. While this wasn�t an issue for our test robot, it would have been for some of our previous designs, requiring upsizing to giant servos and potentially running afoul of the maximum current limits for servo controller port pairs, which could cut the number of usable servos to less than the legal maximum of 12. 

We also found the level shifting cables to be a �kludgey� solution to the 5V-3.3V compatibility issue. Many commercially available sensors and devices work fine on 3.3 Volts, but MR devices, either DIO or I2C, generally don�t, and the motor encoders don�t either. 

With the two Hubs, we used a lot less space for electronics and had an easier time routing wires to avoid getting caught in the launcher mechanism. The switch was very easy and intuitive once we had our wires figured out, and we feel that the REV Robotics Expansion Hub was a much better experience than the previous electronics. Honestly, even factoring in the wiring, our largest time sink was spending 3 meetings trying to reassemble our worm gear system due to a tight tolerance and very small washers.

Q: Your team showcased your robot at the Houston Championship.  How was the new technology received by the people that you met in Houston?

 A: People seemed to be excited by the REV Robotics Expansion Hubs. They keep wire management a lot neater and easier, and take up a lot less space. The only downside that people were concerned about was the lower voltage for the servo ports, but compared to the convenience, it seems like a small issue. The expected cost savings were also favorably received.

Q: What types of questions did people ask you about your robot and about the new REV Robotics Expansion Hub?

A: Most people were most interested in how we like the Expansion Hubs in general, and it�s hard to say much more than they allow for a lot more design space and make everything simpler to map out. 

Q: What does your team enjoy most about its participation in the FIRST Tech Challenge?

A: Overall, all of our members are most excited about getting the opportunity to get hands on and build an awesome robot. Where else do you get an excuse to spend your time using (I�m sure �playing with� isn�t the right term�) tools like bandsaws and milling machines to make something that moves around and does cool things? We also enjoy getting to turn around and talk about it to other teams and the rest of the world, because we love building it, and getting other people as excited as we are.

Q: What does your team have planned for this summer and for the 2017-2018 competition season?

A: This summer we�re looking at doing a series of build challenges we call �Summer Games� to help refine our design process and make it move more smoothly and efficiently, and we also want to help work out a new leadership and notebook system. We�ll be posting the rules and timelines for the games on our Facebook page; they will be �standalone,� meaning that any team can compete on its own and send in scores for comparison later. Summer is also a great time for outreach, which we hope to organize a lot of, and to start work on next year�s VR simulator, which we hope to carry on even though Miyu will have graduated.

For the 2017-2018 season, we will have three new members, and plan to up our game on engineering process, outreach, and ever cooler robot functionality!

If anyone has any questions about REV or just wants to chat, we�re happy to talk. We can be reached at 6220outreach@gmail.com, or our Facebook: FTC Team 6220.

Thank you,

Ian Burnett (6220 Social Media Guy aka "He of the Pink Kilt")