3 CIM Drive Train Battery Draw

[Ether]

Originally Posted by fox46

Your problem may lie in your batteries.

Good point.

How old are they and have you load tested them lately?

Testing the Ahr capacity would be more relevant to the situation Danny has described.

I've seen 12v lead-acid batteries pass load tests with flying colors but fail Ahr capacity testing miserably.

[RoundTabler]

Originally Posted by Ether

Good point.
Testing the Ahr capacity would be more relevant to the situation Danny has described.

I've seen 12v lead-acid batteries pass load tests with flying colors but fail Ahr capacity testing miserably.

Yes. We ahr test our batteries every year. Normally we only use the ones that have 10+ ah. We have a couple batteries from last year we are only using for practice, because we trashed them last year. we had 6 cims, and 2 rs550's, which can use a lot of current.

[Al Skierkiewicz]

I would class 10 AH as trashed and recyclable. What are you using to make the rating determination?

[Ryan Dognaux]

Thanks to Al & the other field management volunteers for talking to our team on Friday & Saturday at the end of the Central Illinois Regional and spending a lot of their time helping us troubleshoot our robot issues. Some of our sporadic performance at CIR was due to what we now think were power issues. We're running a 6 CIM all gear drive through the 3CIM VexPro ball shifters, with an on-board compressor as well that runs for a lot of the match. We switched our jaguar motor controllers to ramp mode to try to help with the immediate 'shock' to the system but that only seemed to be a partial fix. In some matches our CRIO & radio lost power for very short periods of time, effectively taking us out of the remainder of the match as our CRIO rebooted & loaded robot code. We also have some wiring issues (battery & main breaker too far away from the PD board) that we need to fix that may help with this, but we're seriously considering removing 2 CIMs from our drive just so we can function properly at the St. Louis regional.

We also tried to be aware of which batteries we were using when we were having these issues on the field. One of the times we reset occurred while using a 2014 battery; all of our batteries are less than 3 years old & were load tested & shown to be in good condition.

Another mechanical option we're going to implement is removing our outside traction wheels & replacing them with omni wheels, making turning much easier on the robot. Hopefully the combination of all of these changes will yield better results for us at the St. Louis regional.

[z4t143]

I'd like to add my thanks to Big Al and the FMS crew at CIL for their help!

One additional question for Al ... other than the weight penalty, is there any other consideration or FRC rule implication to moving to larger gauge wire on the Battery to PDB loop?

Section 4.8 of the game manual and related figures all reference 6 AWG Wire (min).

It may be easier for us to move to larger wire gauge at this point versus re-arranging components. Thoughts?

[kevin.li.rit]

Originally Posted by z4t143

I'd like to add my thanks to Big Al and the FMS crew at CIL for their help!

One additional question for Al ... other than the weight penalty, is there any other consideration or FRC rule implication to moving to larger gauge wire on the Battery to PDB loop?

Section 4.8 of the game manual and related figures all reference 6 AWG Wire (min).

It may be easier for us to move to larger wire at this point versus re-arranging components. Thoughts?

There's no rule against using a larger wire size but the PD board will only take up to a certain size wire.

[Al Skierkiewicz]

You are very welcome, I wish I could have done more. The wire gauge tables actually double wire size and halve resistance for every jump of four gauges. That is to say that to halve the resistance, you could move from #6 to #2 wire. This is a small change in overall weight compared to the total robot weight. However, you can achieve the same result by halving the length of the #6. This is electrically better and less weight overall. For your robot, this is easily achieved by rotating the PD, and moving the battery and main breaker. It is easier than you think. As I suggested, move the cRio away from the middle of the side of the robot. Replace it with the main breaker which will remove two feet of #6. Rotating the PD (and changing the breaker positions) is very easy as well. The radio and cRio wiring will need to be replaced, which are two of the easiest to change. You can premake those before St. Louis. About the hardest thing to accomplish is the move of the battery. These three things will reduce the #6 length by more than 5 feet I would guess. Added to the removal of one CIM on each side and the addition of some omnis, I bet you get to a point where electrical brownout may be reduced to zero. As a rough guess, with the six CIM drive as you are now, I would expect that the #6 wiring is dropping 2-3 volts on a fresh battery. Added to the 5 volts dropped across the battery internal resistance at this current, that is very close to the dropout voltage for the PD power supplies, the DSC and the 2 CAN. Please let me know if that helps.

[Ryan Dognaux]

Originally Posted by Al Skierkiewicz

You are very welcome, I wish I could have done more. The wire gauge tables actually double wire size and halve resistance for every jump of four gauges. That is to say that to halve the resistance, you could move from #6 to #2 wire. This is a small change in overall weight compared to the total robot weight. However, you can achieve the same result by halving the length of the #6. This is electrically better and less weight overall. For your robot, this is easily achieved by rotating the PD, and moving the battery and main breaker. It is easier than you think. As I suggested, move the cRio away from the middle of the side of the robot. Replace it with the main breaker which will remove two feet of #6. Rotating the PD (and changing the breaker positions) is very easy as well. The radio and cRio wiring will need to be replaced, which are two of the easiest to change. You can premake those before St. Louis. About the hardest thing to accomplish is the move of the battery. These three things will reduce the #6 length by more than 5 feet I would guess. Added to the removal of one CIM on each side and the addition of some omnis, I bet you get to a point where electrical brownout may be reduced to zero. As a rough guess, with the six CIM drive as you are now, I would expect that the #6 wiring is dropping 2-3 volts on a fresh battery. Added to the 5 volts dropped across the battery internal resistance at this current, that is very close to the dropout voltage for the PD power supplies, the DSC and the 2 CAN. Please let me know if that helps.

Thanks Al. We're already planning options of pre-wiring a new PD board in the flipped orientation so we can come in ready to flip it and re-position the electrical layout on Thursday at St. Louis. We'll report back with our results.