Hi there,
Definitely a broad set of good questions, so here we go:
- Reducing resistance usually amounts to increasing wire gauge. >= 6AWG for battery/breaker, >= 12AWG for high current motors (CIMs). We're going to 4AWG for our breaker connection and 10AWG for our CIMs this year since we found wires getting warm last year. Also, reduce wire length as much as possible by placing connected components near each other.
- Creating solid connections: it's overkill, but soldering on crimped terminals is the best way to ensure that they stay on place. We strip off the plastic housing on these terminals, slide on some heat shrink, crimp the terminal, solder over the crimp and then heat shrink. We didn't have a single terminal come loose all season.
- Make sure there's electrical tape or (preferably) heat shrink tubing over any bare connections. This reduces chance for shorting and makes things look cleaner.
- It's often overlooked, but put thought in to where you position the components. Minimize wire length from battery->breaker->PD board (within reason, allowing for ease of battery removal). Keep your motor controllers close to your motors, PD board and cRIO. Keep cRIO near to the digital breakout and motor controllers. Before drilling any holes, set out all the components as a test on a similar sized board to make sure you have an optimal arrangement.
- For testing, provided you guys have enough components to recycle, create a test board with all the electrical fixtures on it. This is a great off-season activity and will save you lots of time during build season when you're not having to kludge together something to test components.
- Get a battery beak for battery testing. It's a one-time cost and has saved us more times than you'd think.
http://www.andymark.com/product-p/am-0995.htm. If you want to get fancy, try putting them through a real world loading test with a test bot and five minutes of drive time after a full charge. Measure the battery's discharge level and keep record of your "best" batteries.
- The new PD board will have current measuring capabilities over the CAN bus, so you can use that for your measurement needs.
- You've learned a very important lesson about engineering: theory doesn't always match experimentation -- and that's okay! There are so many variables in one of these systems: battery internal resistance/charge level, motor parameters, electrical parasitics (R/C/L). If you're not getting the current you're expecting, it's most likely that either your computations didn't take all the variables into account or your experimentation is violating some assumption. Oftentimes, replacing components with "known good" ones is the best way to debug a fault.
- As we found out in elims at IRI, once you've tripped a breaker, it is more likely to trip again. For a competition bot, you'll want to replace it just to be paranoid. Keep that breaker for a practice bot.
- Make sure you have your gear ratios such that you will not pull too much current under the inevitable pushing matches. If you have yourself geared for 20fps with 6 CIMs and you get into a pushing match with a robot (or a wall), you're likely going to pop a breaker. If you've already built the system and there's no time left to fix it mechanically, you can also implement a software limit on how much duty cycle you'll put on the motors. This way, the motor controllers will never actually deliver 100% of the rated power to your motors and it should save your breaker.
Let me know if you have further questions!