6 CIMs and 4 MiniCIMs - Will they stay?

[Andrew Lawrence]

The ability to use 6 CIM motors and 4 MiniCIM motors were a blessing this year, and the majority of teams took advantage of them. However, it was brought to my attention that, like 2010, the extra CIMs from 2013 may not be legal the next year. Personally, I would love for FIRST to continue the use of 6 CIM motors and 4 Mini CIMs; Teams could build 6-CIM single speed gearboxes to compete with the shifters, use the motors to power their shooters, climbers, etc.

What are your opinions on the motor allowance this year? Would you like to see this trend continue for future games? Do you think it's probable that FIRST will continue allowing these extra motors?

[JeffersonMartin]

I really hope they do. 6 CIM drive trains definitely make matches more interesting, and they add the ability to use CIMs on things other than the drive train, without sacrificing to much pushing ability.

[Michael Hill]

I don't think AndyMark would have put that much time engineering a 3-CIM gearbox if it were a 1-year thing. Just my thought.

[Jeffy]

I sure hope so. The fact that the 10 most powerful motors this year had the same mounting and shafts was a blessing.

[Mark Sheridan]

I hope it stays. We used only 6 motors this year thanks to a PTO gearbox, so I want this rule around next year so I can actually use it.

[MichaelBick]

I think the motor rules made the game extra interesting. That said, I'm torn. I think so many powerful motors added to the game, though they also made it easier. I really hope we get at least 2 Mini-CIMs and 4 CIMs next year, but beyond that I feel it is a bit excessive(remember we still have 8 more 500 series motors).

[Anupam Goli]

I don't think AndyMark would have put that much time engineering a 3-CIM gearbox if it were a 1-year thing. Just my thought.

Before they allowed 6 CIMs, several teams used to use FP motors as a 5th and 6th motor in their drivetrains due to similar specs.

[EricH]

Before they allowed 6 CIMs, several teams used to fry FP motors as a 5th and 6th motor in their drivetrains due to similar specs.

Fixed that for you. FPs in the drivetrain will probably end up running at or near stall quite a bit, and they don't like stalling.

[nerdherdmember]

I talked with the people in AndyMark's sponsor stand about them releasing more 3 motor gearboxes and was told that FIRST had not given them any signs about whether or not 6 CIMs would be staying. It does seem logical that at the least some MiniCIMs will remain, as IFI has made a significant investment into that motor, so 4 CIM 2 MiniCIM drive will most likely remain an option.

[DampRobot]

Let me just say this: 6-CIM drivetrains can break the main 120 amp breaker if they are stalled. With a 6-CIM drive, you're essentially giving good defenders a way literally shut your robot down.

As for continuing to have insane amounts of power like we did this year? I sure hope it continues, but I certainly wouldn't take this much raw power for granted. It obviously depends on the game, but I'd bet on 4 CIMs and 2 Mini-CIMs for next year.

[Mark Sheridan]

Let me just say this: 6-CIM drivetrains can break the main 120 amp breaker if they are stalled. With a 6-CIM drive, you're essentially giving good defenders a way literally shut your robot down.

As for continuing to have insane amounts of power like we did this year? I sure hope it continues, but I certainly wouldn't take this much raw power for granted. It obviously depends on the game, but I'd bet on 4 CIMs and 2 Mini-CIMs for next year.

Well you still have to get your gear ratio and traction correct. Having extra motors gives you a few more variables to play with.

[TheMadCADer]

Mini-CIMs and BAG motors are definitely here to stay since they're pretty much replacements for the FPs and Globes. I think the CIM count could vary between 4-6 from year to year, though I do like having more than just 4. However, chances are that we'll continue to only see extra CIMs in years with climbing/hanging endgames.

[Andrew Lawrence]

Let me just say this: 6-CIM drivetrains can break the main 120 amp breaker if they are stalled. With a 6-CIM drive, you're essentially giving good defenders a way literally shut your robot down.

As for continuing to have insane amounts of power like we did this year? I sure hope it continues, but I certainly wouldn't take this much raw power for granted. It obviously depends on the game, but I'd bet on 4 CIMs and 2 Mini-CIMs for next year.

I know a few teams who made a single-speed 6-CIM drivetrain and never had any problems that I've seen (one that comes directly to mind is 973).

[F22Rapture]

Let me just say this: 6-CIM drivetrains can break the main 120 amp breaker if they are stalled. With a 6-CIM drive, you're essentially giving good defenders a way literally shut your robot down.


So can 2 CIMs, or 4 CIMs. As long as you don't gear too high for the amount of torque you have available (which will increase with the number of CIMs), your drivetrain should stay traction-limited and never stall.

[ttldomination]

Fixed that for you. FPs in the drivetrain will probably end up running at or near stall quite a bit, and they don't like stalling.

I'm not sure about this, but there was a discussion and quite a few teams came out in support of this. I think the argument was along the lines of, "they end up doing more work than stalling so it's fine." I don't quite remember.

Either way, I've heard of quite a bit of success from this. At the very least, it's worth exploring.

- Sunny G.

[cgmv123]

I only see the extra motors staying if the available power increases (bigger battery/main breaker).

[EricH]

I'm not sure about this, but there was a discussion and quite a few teams came out in support of this. I think the argument was along the lines of, "they end up doing more work than stalling so it's fine." I don't quite remember.
I know of a couple of very, very good teams that did FP+2 CIMs in the drive for one year and then swore never to do it again. Something about having to replace the FPs--I know one of those teams had to do it on Thursday at a regional and it was a long job, or something like that.

[theawesome1730]

We used all 6 CIMs and all 4 Minis and absolutely loved it. I really hope they continue the use of all 4 Minis even if they drop back to 4 CIMs

[coalhot]

I like the idea of 6 CIMS and 4 MiniCims. However, if FIRST does decide to stay with them, I'd like to see them ramp up the battery size and PDB.

Maybe they'll do that with the new control system. Who knows? :confused:

[MichaelBick]

I know of a couple of very, very good teams that did FP+2 CIMs in the drive for one year and then swore never to do it again. Something about having to replace the FPs--I know one of those teams had to do it on Thursday at a regional and it was a long job, or something like that.

I know 254 and 968 did it 2008 and had problems. We used 550s this year and ran into no problems whatsoever.

Also anyone doing a 6 motor drive needs to make sure they have a traction limited gear

[Zebra_Fact_Man]

I sure hope so.

[cbale2000]

...6-CIM drivetrains can break the main 120 amp breaker if they are stalled...

Does anyone know of an instance where this has EVER happened on a FIRST robot? :confused:

[AlexH]

Let me just say this: 6-CIM drivetrains can break the main 120 amp breaker if they are stalled. With a 6-CIM drive, you're essentially giving good defenders a way literally shut your robot down.


you just gear to break traction before you trip the breaker.

[DampRobot]

Does anyone know of an instance where this has EVER happened on a FIRST robot? :confused:

Yes. 766 shut down 971 in this way at a match at SVR, and we won the match because of it. I have also heard anecdotal evidence of 254 having similar problems.

[Andrew Lawrence]

Yes. 766 shut down 971 in this way at a match at SVR, and we won the match because of it. I have also heard anecdotal evidence of 254 having similar problems.

Maybe someone from 971 can answer this, but what gear were they in (and what speed)? Do you have video of the match?

[DampRobot]

Maybe someone from 971 can answer this, but what gear were they in (and what speed)? Do you have video of the match?

I believe its on TBA. It might have been match 50.

[MichaelBick]

Remember 971 also has 2" wide wheels which give them a ton more traction. I have a hard time believing that they are not traction limited in low gear, but is it possible that in high gear they blow faster because of this?

[Mark Sheridan]

Yes. 766 shut down 971 in this way at a match at SVR, and we won the match because of it. I have also heard anecdotal evidence of 254 having similar problems.

I should know 766 drivetrain since 3309 is running their drivetrain. We are running pretty much the same gear reduction as 254 except with just 4 motors. however we would be more likely to trip the breakers. A big difference was we chose not to groove the colson wheels knowing our gear ratios in both gears were too high to permit that. If we ran 254's wheels, we would have breaker issues big time. We managed our traction and were safe to prevent breaker trips. 3309 tested this ourselves by doing a simulate push test, the wheels always spun in low gear, we could never trip the breaker.

We gotta credit 766's old mentor Scott Baron for teaching us this back in 2005.

[Mark Sheridan]

Does anyone know of an instance where this has EVER happened on a FIRST robot? :confused:

Yeah i did this in 2003. Long wheel base 4 wheel drive with 2 inch wide wheels w/ conveyor tread on them. It was two CIMs and 2 drill motors. Couldn't turn and would pop the breaker from the stall. Would up changing to low traction wheels.

[Cory]

I know 254 and 968 did it 2008 and had problems. We used 550s this year and ran into no problems whatsoever.

Also anyone doing a 6 motor drive needs to make sure they have a traction limited gear

We ran 2 CIM's and 2 FP's in 2006. These were the super awesome 300W FP's that were only rated for 6V, IIRC.

It was a nightmare. We smoked too many motors to count and our drive was unreliable at the worst possible times as a result. We did indeed swear we would never use only 2 CIM's in a drive again (Lunacy notwithstanding).

[Pratik Kunapuli]

Does anyone know of an instance where this has EVER happened on a FIRST robot? :confused:

Yes. We had 6 CIM's for our drive train, and in our first event of the year (Hatboro Horsham), we got into a few pushing matches and popped our main breaker more than twice. When all of our CIM's stalled, they pulled about 780-800 amps for more than a few seconds, which is definitely enough to trip the main breaker.

[Jared Russell]

Yes. We had 6 CIM's for our drive train, and in our first event of the year (Hatboro Horsham), we got into a few pushing matches and popped our main breaker more than twice. When all of our CIM's stalled, they pulled about 780-800 amps for more than a few seconds, which is definitely enough to trip the main breaker.

Worth noting that after replacing the main breaker I do not think we ever had this problem again.

[Tom Line]

I only see the extra motors staying if the available power increases (bigger battery/main breaker).

I disagree.

This is one of those things that teams need to be aware of and design around, as part of the design challenge. I think it's much more real-world to actually have some imposed design constraints rather than having FIRST provide us a system that can be plugged together and won't fail (like Lego League). Even FTC needs to be careful about motor loads.

[Pratik Kunapuli]

Worth noting that after replacing the main breaker I do not think we ever had this problem again.

We were also conscientious that it was possible to trip the main breaker and didn't push for that long the rest of the season.

[Nuttyman54]

Maybe someone from 971 can answer this, but what gear were they in (and what speed)? Do you have video of the match?

We had this issue a few times this year. We are traction limited in low gear, but not in high gear. The instances where this happened occurred when our driver failed to shift down soon enough. Because of the 2 extra CIMS, the breaker blew much quicker than our driver was used to reacting to shift down. If we do a 6 CIM drive next year, there will likely be some mechanical and/or programming solution to prevent this from happening.

[apalrd]

Does anyone know of an instance where this has EVER happened on a FIRST robot? :confused:

It's happened with only 4-motor drives as well.

I personally tripped it in 4 matches during my time as a driver. We also tripped it twice this year. In both cases we had a 4-motor 2-speed drive that was traction limited in low gear.

In other cases, we've seen battery cables heat up and become sticky, and also melted a few robot-side battery connectors (they're only rated for 50a) on practice robots (even with cool-down times between batteries). We used 4-gauge robot-side battery cables to hopefully improve this, and did not melt anything this year.

[thefro526]

Does anyone know of an instance where this has EVER happened on a FIRST robot? :confused:

As Jared and Pratik said above, it's happened to us at least once this season. Took a good bit a defense to pop it, but it can happen. There are a handful of other teams that have complained of popping breakers as well, most of which are using high traction drives with 6 CIMs or 4 CIMs and some additional motor.

Looking back, I'm fairly sure that prior to this year electrical shorts were the most/more common cause of the 120a breaker tripping, but I'm not sure.

you just gear to break traction before you trip the breaker.

There's a bit more to it than that. In a perfect world, when you break traction between the drive wheel and surface (carpet) the motor would then essentially spin at free speed and draw little to no current (see 2009) but with carpet that isn't the case.

More often than not, a wheels static COF is what's being used for current draw calculations rather than it's dynamic COF - which makes sense for seeing if you're traction limited. Most of the time, when people design something to be traction limited, it's so that they know that they won't have an issue in the off chance that their motors are stalled due to some interaction with an immovable object for a reasonably short period of time. Usually, this is all you need to do as long (more than a few seconds) instances of high load like that are pretty uncommon in recent FRC games.

There are occasions where you need to go a bit deeper into the issue than that. Once your wheels have broken traction with the carpet, the wheels Dynamic COF starts getting important. Most wheels have a Dynamic COF that's significantly lower than it's Static COF, but there are some wheels that don't so it's best to try and dig up some hard numbers first. Anyway, once you're out of the traditional traction limited realm and Dynamic COF starts coming into play, you'll see that the motor is still under a decent amount of load and will draw the appropriate amount of current. Depending on the setup, this can be (probably is) enough of a current draw to start tripping breakers (either 40A or the 120A main) after a few seconds.

One more thing to be aware of: The weight/normal force on your robot's drive wheels may increase during a pushing match. This is especially true for low bumper robots pushing high bumper robots as the bumpers tend to ride onto one another. You might be traction limited at normal weight, but what if an additional 60lbs or so is on top?