3 CIM Drive Train Battery Draw

[RonnieS]

Originally Posted by kevin.li.rit

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

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.

[Anthony Galea]

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.

[robohead456]

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.

[geomapguy]

Originally Posted by robohead456

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.

By 8 CIMs you mean 6 CIMs + 2 MiniCIMs?

[JamesCH95]

Originally Posted by kevin.li.rit

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

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.

[kevin.li.rit]

Originally Posted by JamesCH95

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.

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.

[JamesCH95]

Originally Posted by kevin.li.rit

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.

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.

[robohead456]

Originally Posted by geomapguy

By 8 CIMs you mean 6 CIMs + 2 MiniCIMs?

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

[Al Skierkiewicz]

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.

[geomapguy]

Originally Posted by robohead456

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

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

[Brian C]

Originally Posted by robohead456

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

Are you sure it was 8 CIM's?

Is that your final answer

[yash101]

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) . 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!

[Brian C]

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..

[Andrew Schreiber]

Originally Posted by yash101

3 CIMs only become useful if your robot is playing tug-of-war (or push of war) .

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.

[Ether]

Originally Posted by Andrew Schreiber

Straight up wrong.

Caveat lector:

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) . 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

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