3 CIM Drive Train Battery Draw
 

We've only ever used 4 CIMs on our drive train before this year so I was thinking, with 2 extra CIMs, have teams noticed a shortened battery life?

Specifically, when your're running all out in a match, has it been an issue?

Re: 3 CIM Drive Train Battery Draw
 

We haven't noticed a big difference with ours but we are running 2 cims and 1 mini cim...our winch has the other 2 cims so we use all jags with CAN; we can then use current sensing so we can slow the line power while drawing back. We also have optimized auto shifting to help be most efficient ;) . We love the acceleration though::safety::

Re: 3 CIM Drive Train Battery Draw
 

Well, unless the battery has reduced capacity I still don't think you'll run out.

You have a 120A breaker on the robot which is already limiting your current draw. A fully charged 17AH battery is not going to run out in 2.5 minutes

Re: 3 CIM Drive Train Battery Draw
 

It wouldn't "run-out" but more drain a little faster and depending on how a team makes their mechanism, it could alter its effectiveness.

Re: 3 CIM Drive Train Battery Draw
 

Last year, we used a 3 CIM drive train (6 total), with 2 BAG motors and 1 Andymark motor, all at once and we did not find any performance drop, throughout any match. We trust it enough to use it again this year, if that makes a difference.

Re: 3 CIM Drive Train Battery Draw
 

Last year my team used 8 CIM motors in addition to a window motor. The battery lasted throughout the match, but to be sure, we charged it immediately after and used a different battery for the next match.

Re: 3 CIM Drive Train Battery Draw
 

By 8 CIMs you mean 6 CIMs + 2 MiniCIMs?

Re: 3 CIM Drive Train Battery Draw
 

It might be quite rare, but it is possible. 95's 4-wheel swerve robot in 2002 could easily drain a battery in a single match if everything wasn't just perfect. A reasonably high, steady, current draw can definitely deplete an FRC battery in 2.5 minutes or less.

Re: 3 CIM Drive Train Battery Draw
 

We used 4 CIMs for driving the robot and another 4 to pull it up the pyramid.

Re: 3 CIM Drive Train Battery Draw
 

I know of several teams that have tripped their main breaker with six CIM drive trains in addition to other motors. If you don't monitor current at some point in your design and build phase, this will turn out to be a risky choice. Drawing 120 amps continuous for 2 minutes will not only draw the battery down, it will at a minimum shorten it's life and likely will cause some internal damage. Even to assume that the Amp Hour rating will be derated by 40% by the higher draw leaves you potentially, with just a few minutes before the terminal voltage falls below the critical 5.5 volts when the DSC stops working or the 4.5 volts when the cRio power supply goes away.

Re: 3 CIM Drive Train Battery Draw
 

Still not being clear..... 4 CIMs and 4 MiniCIMs??

Re: 3 CIM Drive Train Battery Draw
 

Hmmm, wasn't the breaker that year at 80A? I suspect the RC or radio was losing power as the battery was drawn down. No dedicated supply for the radio or backup battery for the RC to prevent it from resetting.

Re: 3 CIM Drive Train Battery Draw
 

It was a 60A main breaker. Like the current 120A main breaker it was tolerant of large over-currents for prolonged periods of time. I don't recall that robot ever blowing a main breaker.

Don't get me wrong, resetting also happened (at around 6V IIRC). More than once. The next year we got back-up batteries... and not long after that we got 120A main breakers too.

As a student on the pit crew for that robot I distinctly recall checking battery voltages after matches (where the robot was driven a lot) and reading 9-10V floating on the battery.

The big SNAFU with that robot is that we used worm gears to get lots of gear reduction in the small space on our swerve modules, and if anything was a tiny bit out of alignment the drag from those gear-sets could cause ~40-60A no-load draw, and it could be more if the steering motors were active.

Re: 3 CIM Drive Train Battery Draw
 

Are you sure it was 8 CIM's?

Is that your final answer ;)

Re: 3 CIM Drive Train Battery Draw
 

The CIM's each only draw how much power is required to accelerate the bot. 3 CIMs only become useful if your robot is playing tug-of-war (or push of war) :D. The CIMs are rated at 67A/hr? That doesn't mean that they will always use 67 amps. That is what will happen on full load, and I think you have other things to worry about by then! ;)

Re: 3 CIM Drive Train Battery Draw
 

We ran in our 3 CIM gearboxes over the weekend. Measured with a DC clamp on ammeter the total currrent draw for all 3 motors on an unloaded transmission was 9.2 amps. The funny thing is when checked individually 1 motor was pulling 4.4 amps, the next was at 3.3 amps and the 3rd was at 1.5amps.

When the next transmission was run in we found similar readings as well. The same motor positions in both transmissions had the same basic readings inasmuch that they went from a high current draw to a lower current draw based on their mounting position. The readings only varied by a few tenths of an amp.

After checking gear lash there were no significant differences when run again. These are the AndyMark 3 CIM upgrades for the AM14U chassis..

Re: 3 CIM Drive Train Battery Draw
 

Straight up wrong. We're rocking 3 CIMs in our DT and have 0 intent on pushing anyone. They provide more torque which allows faster acceleration given proper gearing. And let me just say, this beast drives far different than anything I've played with.

Re: 3 CIM Drive Train Battery Draw
 

Caveat lector:

... The rest of the post was straight up wrong as well.

Re: 3 CIM Drive Train Battery Draw
 

The past three years I've been involved with a couple teams using 6 motor drives:

2011

Cybergnomes#2013: 4x CIM + 2x RS775 on Single speed 8x8 drivetrain, 1xRS550 arm stage 1, 1xRS375 arm stage 2, pneumatic gripper.

2012

Cybergnomes#2013: 4x CIM + 2x RS775 on Single speed 8x8 drivetrain, 2x RS550 shooter, 1x AM9012 Conveyor, 1x Window motor pickup retract, 1x RS545 feeder, 1x RS375 Azimuth control.

Ramferno#3756: 4x CIM + 2x FP0673 on single speed 10x10 drivetrain, 2x RS550 shooter, 1x window motor feeder, 1x RS550 conveyor, pneumatic pickup retract.

2013

Cybergnomes#2013: 6 CIM drive single speed on 6x6 drivetrain, 2 MiniCIM on climber, 1 MiniCIM Shooter, BAG Motor Azimuth control.

Never once did we experience a main breaker trip. All machines since they were single speed drivetrains were geared to operate at the limit of traction. They had great acceleration, good *controllable* speed and phenomenal torque. As far as pushing power, they were on-par with the 2 speed 4 motor drivetrains. However, when in a prolonged shoving match they did eat much more power than the 2 speed drives. The behavior we noticed is that if the drivetrain managed to stall (was designed to break wheels free first but on a weakened battery it would occasionally happen), since no three DC motors are exactly the same (why BrianC was getting different current draws during no load) it seemed that the 40A auto-resetting breakers would trip in a cascade fashion. One would go (highest draw motor) which would increase the load on the other two whose breakers would respectively follow suit.

Personally, I think 3 motor 2 speed is a waste of money unless you can generate enough traction through mechanical interaction with the carpet to warrant it. Single speed 3 motor has the benefit of being able to compete with multiple ratio transmissions if geared properly because we are all limited by weight. Remember: force of friction (traction) = normal force (weight) x coefficient of friction (gum rubber on carpet in best case). Since we can't use studs or an apparatus to "claw" at the carpet, every robot is more or less limited in traction by its weight. Where the single speed shines is its ability to go whistling across the field, HIT a robot thus exceeding its static forces of traction with the carpet by overwhelming it with momentum and then "freight train" it across the field without ever letting up or shifting.

That being said... 3 motor 2 speed would allow you to wrestle with other robots without using as much power and with very little worry about tripping any breakers.

Instead you can worry about peeling the tread off your wheels and incurring penalties for damaging the field surface.

For this year, we are again building some very power-hungry robots and I am somewhat concerned about power draw myself but if past experience is any indicator, there shouldn't be too much to worry about. We may be implementing some current-saving techniques like shutting down the compressor or even two drive motors while reloading *the primary weapon* but all in all I would not be too worried.

One thing to mention though, keep an eye on your batteries. 6 motor drives WILL bring a frail battery to its knees during competition so be wary of that old grey battery that your team has had kicking around from 3+ seasons ago.

Re: 3 CIM Drive Train Battery Draw
 

Please do a LOT more homework before posting information like this. What you posted was terribly incorrect information.

6 cims can accelerate a robot faster than 4 cims, so they draw more power total.

Cims are not 'rated for 67A/hr'...motors aren't rated by charge capacity, batteries are.

Cims won't always use 67A, but at stall (maximum torque) they can draw 133A. At peak power output they will draw 68A.

Re: 3 CIM Drive Train Battery Draw
 

And, when batteries are so rated, the units are not amperes per hour, they are ampere hours.

Re: 3 CIM Drive Train Battery Draw
 

Correct as always Ether! A*hr, not A/hr

Re: 3 CIM Drive Train Battery Draw
 

A circuit breaker doesn't limit your current. It will give you all the current you want until you hang yourself and it trips out.

Re: 3 CIM Drive Train Battery Draw
 

Well if were being nit-picky about my wording. The circuit breaker doesn't give me any current, it allows all the current to pass through it.

Re: 3 CIM Drive Train Battery Draw
 

I disagree with you saying it was nit-picking. Saying it is limiting your current implies it will somehow reduce current draw if it goes above 120A. Whereas, what really happens is if you go above the limit for too long, the breaker will trip and cut out everything on your robot. The second one, which actually happens, is obviously worse.

Re: 3 CIM Drive Train Battery Draw
 

We ran 6 CIMs on our drive train last year and are running 4 CIMs + 4 MiniCIMs on our drive train this year.

Yes it will can eat batteries, we plan to buy 6 new batteries every year, it's just simpler that way and we know we have good batteries. We donate some of the older ones to rookie teams, they still work pretty well but we know they have been run very hard.

For our first two events we were traction limited but our top end speed couldn't keep up with the likes of 118 and 1477. We changed our gearing for Razorback and IRI and knew that if we went for too long in any pushing match we would blow the main breaker or brown out. We still got in pushing matches but we actually had our driver trained to react to the underglow on our robot. It was run directly off the PD board so when voltage would dip low enough to completely kill the lights we knew we only had about 1.5 secs before we would likely brown out the radio. It took some drive practice to get the hang of it but we only blow the main breaker once (that was when we ran into the pyramid and it might have been due to shock and not current) and we browned out in our first match at IRI and never again.

It's entirely doable to run 6+ motors on your drivetrain and can be very advantageous but understand that there our trade offs.

Re: 3 CIM Drive Train Battery Draw
 

You're right it doesnt control the current but it does reduces it to 0 if you go above 120A for too long. In my mind that is a limit.

Re: 3 CIM Drive Train Battery Draw
 

Make EXTRA sure your Battery is fully charged. (at 12 Volts). Today we were at 11.89 and the CIMs started to lag after 30 seconds. They really do take a lot of battery power.

Re: 3 CIM Drive Train Battery Draw
 

Fully charged is well above 12volts, we rarely will start a match with a battery below 12.8 volts.

Re: 3 CIM Drive Train Battery Draw
 

I'm noticing significantly less charge over time than I'm used to, but we are running 5 cims (4 drivetrain, 1 intake). Mostly our high-load fast paced practice with lots of intake run has seen this drop. We're running it a lot more in practice than I expect to under live fire, but I will continue gladly enforce my "1 match, 1 battery" guideline for my team. Can't risk running low and killing effectiveness.

That being said, I still don't expect noticeable voltage drop with less than 3 minutes of intense play like previous years for most teams. I think I've only run one robot in competition doing 2 matches per battery, and that was the unmentionable year, where we had, IIRC, only 3 motors.

Re: 3 CIM Drive Train Battery Draw
 

Unless you have 3 XU's like 1706 XD. That would draw some power!

Re: 3 CIM Drive Train Battery Draw
 

I thought there was a 6 CIM limit?!



What's wrong in it? Maybe the 67AH, but that has a question mark of uncertainty on it. It's just go get the point.


Isn't that what I said?! Also, I was referring to the draw (i don't know exactly how to express it). However, I think it should have been understood by the context.

Re: 3 CIM Drive Train Battery Draw
 

I could not understand what you said.
Please do research before you post. If you don't know something, then research and ask questions rather than risk posting false information as fact.
DC motors current draw is inversely proportional to speed. When speed is zero (i.e. stall), current draw will be greatest. When speed is greatest (i.e. free speed), current draw will be least. In the case of CIM, it will draw 133 amps at stall, and 2.7 amps at free speed. It doesn't draw 67 amps per hour, nor 67 amp*hours. Take a look at motor curves. This Instructable explains it well.

Re: 3 CIM Drive Train Battery Draw
 

No, you said that a 6 CIM drive only makes a difference in a pushing match, which isn't true.

Re: 3 CIM Drive Train Battery Draw
 

Guys,
When you take a battery directly off a charger and add it to your robot, the dashboard will report a terminal voltage of something higher than 12 volts. This will rapidly fall to a nominal voltage once you start to draw some current. This is a well documented condition, even here on CD. This is not an indication that the battery is any better than another battery, simply that it has some "surface charge" from the battery charger. Lead Acid batteries require a charger to have a higher voltage to push charge current into the battery.

Re: 3 CIM Drive Train Battery Draw
 

We have 2 CIMs on each side of our 8-wheel DT (one of the AndyMark systems) and we're sucking battery so fast we can only go about 3-4 minutes before we see noticeable voltage drops on the batteries and the system becomes sluggish. We've not been battery hogs like this in ... ever. Yes, everything has been lubed properly.

<shrug>

-Danny

Re: 3 CIM Drive Train Battery Draw
 

Danny,
Something that doesn't come up in these discussions that should be. When you charge a warm battery, it sometimes fools the charger. To make sure you get max charge, let the battery cool down after you take it off the robot for 30 minutes or more. Also, lots of traction/friction with the floor will eat batteries in turns. If you are doing a lot of turning, this will also affect battery life.

Re: 3 CIM Drive Train Battery Draw
 

What is your gear ratio (from motor all the way to the wheels) and wheel diameter?

Re: 3 CIM Drive Train Battery Draw
 

Your problem may lie in your batteries. How old are they and have you load tested them lately?

Re: 3 CIM Drive Train Battery Draw
 

The question should be rephrased.

It's not "should we use 3 CIMS instead of 2?" but "Do we have weight for 3 CIMS?"

From my experience, a 6 CIM drivetrain performs better period. One of the things it improves very noticeably is turning.

Re: 3 CIM Drive Train Battery Draw
 

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.

Re: 3 CIM Drive Train Battery Draw
 

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.

Re: 3 CIM Drive Train Battery Draw
 

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

Re: 3 CIM Drive Train Battery Draw
 

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.

Re: 3 CIM Drive Train Battery Draw
 

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?

Re: 3 CIM Drive Train Battery Draw
 

No, you didn't. Not unless every inspector at your event was asleep the entire time. Double check with your team, and you'll find you used at least a couple of mini-CIMs.

Re: 3 CIM Drive Train Battery Draw
 

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

Re: 3 CIM Drive Train Battery Draw
 

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.

Re: 3 CIM Drive Train Battery Draw
 

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.