Hi ,

Here's some updates and news from FIRST^® Tech Challenge.

In this week's blast: 

💻 Tech Tip of the Week

🏆 Championship Corner

❌ FTC-ML Site Closure Reminder 

🔧 Upcoming FIRST^® Dashboard Maintenance

Tech Tip of the Week

This Tech Tip of the Week is Part 3 in a 3-part series surrounding a question that we get asked at events all the time - “What makes battery voltage sag?”. As a battery is heavily used, teams will notice that the voltage of the battery temporarily decreases from its starting voltage during periods of heavy use, and then generally raises back up once the heavy use has subsided. So, what causes this?

There are LOTS of reasons why battery voltage will sag during use. In Part 1 we talked about battery chemistry to give an idea how a battery works, and we talked about how motor torque is inversely proportional to the power consumption (given a constant load). Part 2 covered cell health and battery temperature, both of which can affect a battery’s performance and longevity. This week, we will cover another major factor, which is Internal Resistance (IR).

Understanding IR requires talking about the discharge rate of a battery. The discharge rate is a measure of how quickly the battery can deliver its stored energy. Most NiMH batteries used in FIRST Tech Challenge are rated at a nominal 12V and a maximum discharge rate of 30A, though that rate is limited by the 20A fuse. A battery’s IR refers to any opposition to that flow of electric current within the battery itself.

Resistance can come from a number of sources, such as resistance within the battery’s chemistry (such as a breakdown of the conductive electrolyte within the battery), changes to the resistance of the electrodes (such as a buildup of crystals around the electrodes), resistance added due to connectors and wiring, and others. Rising IR affects the battery performance primarily in decreasing the Voltage and Current that the battery can provide and causes the battery to generate excess heat when used.

The starting IR of a battery can vary among different manufacturing processes and batches, so much that batteries should have their IR measured (using a CTR Battery Beak, West Mountain Radio CBA, or similarly capable battery tester) at “birth” (when “new” at time of purchase) and the IR then should be tracked over time. Once the battery’s IR increases by 50% from when it was “born”, the battery is considered ready for replacement. 

What can teams do to slow the increase in a battery’s IR? Naturally, the battery’s IR will change as the battery ages, increasing due to chemical changes and wear and tear. The temperature of the battery can also have a negative effect on IR, higher temperatures cause higher resistance (so keep your batteries cool!).

It is also important to note that the state of charge of a battery can change the IR, battery IR should always be measured fully charged. But the most important ways to keep your battery healthy are to avoid deep discharges (avoid letting your batteries drain below 10V steady-state, definitely never below 9V!), use a high-quality charger that prevents batteries from overcharging, follow the battery manufacturer’s recommended charging procedures, and use low-resistance connections (thick wires and clean connectors!).  

Finally, the IR of NiMH batteries can also sometimes be decreased through a process known as “battery conditioning” (also referred to as “charge cycling”). If IR within a battery is raised due to crystal formations inside the battery, this process of conditioning can help break down those crystal formations and improve Voltage and the flow of current in a battery. Some chargers have automatic conditioning modes, but always refer to your manufacturer’s recommended procedure for charge cycling your NiMH batteries. 

Championship Corner

Championship Conferences

Attending the 2024 FIRST Championship presented by BAE Systems? Join us for FREE conferences April 17-19 on a wide variety of topics such as program specific resources, workforce development, school, and education implementation, FIRST sponsor content and more! Download the 2024 FIRST Championship App to see the full conference schedule.  

FIRST Championship Information 

If your team is joining us at FIRST Championship make sure to check out the 2024 FIRST Championship website and download our 2024 FIRST Championship App to stay up to date on all the event  information.

You'll want to read through our FIRST Tech Challenge Event Guide Addendum for the latest and greatest information about FIRST Tech Challenge at FIRST Championship! 

FTC-ML Site Closure Reminder 

The FTC Machine Learning Toolchain, https://ftc-ml.firstinspires.org, will be shutting down for the season on Monday, May 6 2024.

Unfortunately, due to site maintenance costs we cannot keep the toolchain available during the off-season. However, this summer the site will be undergoing necessary maintenance for next season, and once the maintenance is completed those watching the fmltc GitHub repository should be able to migrate their instances to the new infrastructure.

As with all end-of-season closures, access to the site will be unavailable during the closure and all uploaded and generated data in team accounts will be deleted before reopening on kickoff next season.

Upcoming FIRST^® Dashboard Maintenance

The FIRST Dashboard will be unavailable while undergoing scheduled maintenance from May 5 – May 14. Access to Team Rosters will be unavailable during that time. If you will need your team roster May 5 – May 14, we suggest printing it prior to Dashboard maintenance.