My team says that using 6 Cims draws too much power but it seems like most teams used 6 Cim drivetrains in Steamworks. Is it running low on power really a problem? I’m wondering how so many other teams are able to manage it.
291 ran a 6 CIM, 19 fps (actual speed) drive last year… we absolutely murdered batteries. We were fine for 2.5 minutes, though we did not have much else consuming power on the robot.
Take a closer look. There’s 6-CIM and X-CIM and Y-MiniCIM, where X+Y = 6. MiniCIMs look a lot like CIMs, but they’re just a little bit shorter lengthwise and about 2/3 the power.
The issue tends to be that the robot draws enough current to draw the battery down to “brownout” conditions. If you get a brownout, your drivetrain loses power because the robot is trying to keep the RoboRio (and radio) alive and talking. One or two teams have, IIRC, reported nearly or actually tripping their main breaker when using 6-CIM.
What you might want to do is consider a 6-MiniCIM drivetrain…
Was there a big difference to performance between the start of the match and the end? Could it have been something that would prevent you from getting a climb?
Even with our excessive power draw throughout the match, we never ran low enough on power for it to affect our performance. We climbed in 3 seconds every match. Sometimes we would brown out toward the end, but with newer batteries that wasn’t an issue.
What exactly is X and Y Cim? is that a mix of full and mini Cims in a drivetrain? If you did 6 mini cims, wouldn’t that have the same power as 2 normal Cims?
Take a look at this white paper from fall 2017 and this white paper from fall 2014 from my old team. The thread from 2017 shows that there is almost no difference between the 4 CIM drive train and the 6 CIM drive train in terms of joules. It actually shows that the 4 CIM + 2 Mini CIM drive train uses more power in joules than the 6 CIM drive train. But, it also shows that the 4 Mini CIM drive train and 6 Mini CIM drive train draw less power than the 6 CIM and 4 CIM drive trains respectively. So basically, if you are going to use CIMs, you might as well use 6 because the difference between 4 and 6 are very small, but using Mini CIMs will use less power than the CIMs. It also shows that you shouldn’t use a combination of Mini and Full CIMs if power is your issue.
So if I read that correctly, there is such a small difference in performance between 6 and 4 CIM to just go with 4 cim for lower weight and simplicity?
There are a lot of variables here. It’s entirely possible to create a 4 CIM drivetrain that trips breakers and browns out, and a 6 cim drive that runs happily.
95 ran 6 CIMs at 18fps single speed last year.
By the end of a match things were getting a little hairy trying to turn in place, but the drive train was 6 colsons with no center drop so that’s unsurprising.
We used 2 gauge wire in place of 6, and that got us back about .1v. We also mapped a button to force the compressor off, which got us a little more performance at the end of the match for aligning and climbing.
If it’s at all telling, we’re planning on using 6 mini-cims and a two speed transmission this year.
Perhaps your team figured the strategy much differently than we did, but the relatively benign field (compared to STRONGHOLD) and a few protected zones means that this year does not seem to call for the large amounts of torque enabled by 6 CIMs or 8 775s.
If you do go either of those routes, at a minimum you should use SRXs and current limiting so that your whole robot isn’t drawing more than about 200A. By at a minimum, I mean that this is the simplest thing that should work. There are plenty of more intricate power management strategies that could also work.
Power is measured in watts, not joules.
Could you please clarify?