6 CIMs and 4 MiniCIMs - Will they stay?

Originally Posted by DampRobot

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]

Originally Posted by Andrew Lawrence

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?

[Nuttyman54]

Originally Posted by Andrew Lawrence

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.

[Mark Sheridan]

Originally Posted by DampRobot

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]

Originally Posted by cbale2000

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

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.

[Pratik Kunapuli]

Originally Posted by cbale2000

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

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]

Originally Posted by Pratik341

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.

[Pratik Kunapuli]

Originally Posted by Jared341

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.

[apalrd]

Originally Posted by cbale2000

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

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.

[AlexH]

Originally Posted by 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.

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

[Anupam Goli]

Originally Posted by 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.

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]

Originally Posted by Wing

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.

[ttldomination]

Originally Posted by EricH

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.

[EricH]

Originally Posted by ttldomination

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.