Experience With 6 Cim Drive train
 

I am looking for some real world feedback on teams experiences using a 6 cim drive train with a 2 speed transmission designed for both low speed (4-5 ft/sec) and high speed (say 14ft/sec).

If your robot got in an extended pushing / blocking match with other 6 cim robots for a good part of a match...

- Would you be at risk of blowing the breaker ? If so, how often did you blow your breaker last year. Did you replace the breaker one or more times last year. Have you implemented any software protection (reduce power after X seconds) or hardware (fan) to defend against that ?

- how warm or hot would the following be by the end of the match
- the battery
- the terminals on the battery
- the contacts of the battery connector
- the breaker, its terminals etc

- do you guys do anything to cool the cims (fans, aerosol can cooling for example)

I have heard of a team that replaced all the 14 gauge cim wires with 10g wire. Did you guys do anything like that ?

If the cim motors are stalled in a pushing match (and apparently drawing close to 100amps each), does anyone know for certain if the 40amp breakers trip at all (and reset seconds later) reducing some of the potentially 600 amp+ current off the main breaker. Maybe not if the 40 amp CIM breaker is overloaded 2.5 times (100amps / 40amps) versus 4.8 times for the main breaker (600/125).

What was your teams experience ? Thanks

Re: Experience With 6 Cim Drive train
 

Hiya. 3061 used a 6-cim last year with A high gear of 21 fps, and a low of 7 (This is nuts don't do it)

We had no problems whatsoever with the battery or connecting wires getting hot. That said, we killed the main breaker whenever we hit anything in high gear for too long.

We used compressed gasduster to cool cims during eliminations.

Re: Experience With 6 Cim Drive train
 

Our robot used 6 Cims this year. We used VexPro Ball shifters with total reduction being 5.5fps and 15.5fps. (<- not sure if accounting for inefficiencies). Our Drivetrain setup was a 6wd tank drive with 3" Colson wheels and non-cantilevered axles. It is worth noting our center of gravity was within 5" of the floor.

We played extensive defense all year. We tripped the breaker one single time all year, and that was playing at Texas Robot Roundup after 2 regionals, and a prior off-season event. During the season, we had absolutely no breaker problems.

I will try to dig up some video, if you would like.

For your questions.
-The battery was a few degrees above room temperature, the plastic casing was no hotter that a battery just off the charger. (When swapping robot batteries there was no thermal way of telling them apart from the casing)
-Our battery terminals are heat-shrinked and taped up so the metal itself is untouchable. I will say the whole lead assembly from the battery to the PDB was significantly warm, but you could comfortably leave your hand on them.
-We have never had any issues related to the battery connector, and, like I just said, these were also warm but not concerning.

We did not have any form of cooling; no sinks, no fans. After a match the back of the motor (where the brushes are) was too hot to touch for more than a second, but the rest was ok. (By the next match the heat had mostly dissipated). I think we will seriously consider some form of thermal dissipation in the future. We may put one of the large computer fans on the bunch of 3, or make our own heat sink. We do not find the heat sink the KOP had particularly useful, because like I said, it is the back of the motor that needs cooling, not the main casing. While those would help, the heat does not propagate that far to make them useful in my experienced opinion.

We did practice our robot for about 2 hours straight, with nothing but some 30 second battery changes every 5 minutes. By the end, you could easily boil water with those things, they were roasting.

Re: Experience With 6 Cim Drive train
 

We used 6-CIM ball shifters (with 2 CIMS and 1 MiniCIM each) on our robot this year. We had no problems with breakers when driving in low gear. There was one occasion that the main breaker was tripped during a hard collision in high gear that could have been attributed to a current spike (or just the force of the collision, we're not sure), but beyond that we had no issues that I'm aware of.

I'm hoping the current monitoring capabilities of the new PD board next year will make it really easy to manage current draw and maybe even allow us to program automatic down-shifting when current draw gets too high.

Re: Experience With 6 Cim Drive train
 

We had 6 cim single speed at 11 fps and were traction limited with versa wheels. Never tripped any breaker.

Just my opinion, but for the short duration of FRC matches, the low gears on 3 CIM gearboxes have way too high of reduction for robot movement (if the goal is preventing a breaker from tripping). However, if that slow speed is part of the design strategy of the game, that is a different story.

Those breakers can take some heat, let them get a little toasty, especially since FRC is held during the winter.

Re: Experience With 6 Cim Drive train
 

20 used a shifting 4-CIM, 2-MiniCIM drive geared for about 6 and 16 ft/s in 2014.
We loved it's performance for most of the season.
The only issues we had were when our driver forgot to switch into low gear when we were playing defense in our second qualification match at our first regional. We ended up tripping our breaker that match.
The gearboxes themselves took a lot of damage as well throughout the season, but that was because our driver drove the robot like he stole it.

Re: Experience With 6 Cim Drive train
 

I'm really excited for the new current sensing ability we'll have next year. It will let us automatically shift of we see too high of current.

Re: Experience With 6 Cim Drive train
 

I certainly disagree with that. I find shifting to a low gear (<7fps) to be a very valuable asset, in more situations than just precise movement.

While our 5fps was definitely too slow to play the whole match in, there were numerous times (especially in the defense heavy game) that you just needed to knuckle down and bulldoze your way through a pileup. Our robot used 3" Colson wheels, had the bumpers at the lowest point, and had a center of gravity roughly 5" from the floor. We could push nearly everyone, and many tank robots saw themselves skidding sideways by us. We did not have a traction problem at that torque either, and our used wheels had little measurable diameter difference to new ones, to the naked eye.

Also, on the topic of generic shifting; Being able to change gears gives you the ability to have a high upper stage (like 16+). Many people had 18fps upper stages or more. If you had a single speed gearbox, I think most people would agree (game dependent, but for 2014 in this) that having only a 18fps gear would not have been a good idea. But certainly most people who had 18fps high gear shifters would agree that it was a great gear knowing you could summon the torque when you needed it.

Re: Experience With 6 Cim Drive train
 

This past year we had a 4 cim ,2 minicim vexpro ballshifter west coast drive and we were geared 18 high and 12 low fps we had absolutely no problems with popping breakers. We also had no problems with pushing in high gear although our engineers warned against. Our center of gravity was within 5 inches of the floor . The only thing that reached above 18 inches on our robot was the superlight floor intake and catapult in a nonshot position.

Re: Experience With 6 Cim Drive train
 

So then the other positive is pushing correct?

There are a lot of factors involved but just to be simple, the system doesn't need to be designed to 40 amps per motor to push someone. That's why I said the low gears are too low. They are over designed for the 150 second matches to push people around, and too slow to be useful in normal driving.

I would say you can comfortably design them around 60-65 amps per motor to push, based on what we saw our drivetrain do this past year. I would like to try 70-75 amps per motor this year and see what the breakers can take, should be fun.

Re: Experience With 6 Cim Drive train
 

Readers of this thread might be interested in this one from 2013.

Re: Experience With 6 Cim Drive train
 

Is this the gearbox you used? If so, how did you achieve a 1.5x spread?

Re: Experience With 6 Cim Drive train
 

1687 ran 6 CIMs single speed last year, at 14.5 fps, riding on colsons with a linear tread pattern, playing some real tough defense all year long. At our first event, we tripped the breaker once in our final match, at our second, a couple more times. After that, we looked for ways to eliminate breaker trips for our offseason events. Retrofit shifters were designed, but for various reasons, couldn't be manufactured in time. Instead, we made several minor mechanical, electrical, and software tweaks to reduce current draw:

• Doubled the number of air tanks on the robot, reducing required compressor runtime
• Systematically tested every pressure switch we own to find the one with the best combination of high cutoff pressure and low startup pressure, again reducing required compresser runtime
• Switched our intake extension, our largest source of air use, to single acting pistons
• Upped wire gauge in several places in the robot, reducing losses due to wire resistance
• Coded our drivetrain to automatically drop to 4 CIMs when running our shooter winch or intake motors, with the driver given a trigger to override this in high-pressure situations
• Added a trigger for our driver to shut off the compressor regardless of pressure during pushing matches
• Added ramping to drivetrain which limited sudden accelerations and abrupt direction changes slightly

Did not trip the breaker after this. However, we do plan to use shifters in the future, or gear lower if the game does not call for the speeds we geared for this season.

Re: Experience With 6 Cim Drive train
 

Had essentially this exact same experience with a 6CIM SS geared for that speed. Instead of the measures described here, though, we simply changed our gearing to ~11fps. No more breaker problems after that.

Re: Experience With 6 Cim Drive train
 

That wasn't an option for us because our gear box was constructed single stage and already pushing geometric limits for that configuration, our robot was not set up to accept a COTS single speed gearbox, and manufacturing our own wasn't an option for the same reasons as for shifters. That's the quick solution though!

Re: Experience With 6 Cim Drive train
 

Great! 6 cims driving 3 cim ballshifters geared 12ft/sec and 5.5 ft/sec. Kit drivetrain upgraded to 8wd long. Traction limited in high, estimate of around 200 amps spinning in high using drivetrain calculator on WCP website. Played tough D in high a lot at central il regional, no trips. No trips at Wisconsin either. Standard wiring sizes, noticed some heating in wiring and battery, no failures, no major concerns. 6 cim acceleration made for some great defensive capability.

We will seriously consider 6 cim single speed next year at 12 ft/sec unless game dictates otherwise.

Heres a short video showing some highlights from cental IL for those interested:
http://m.youtube.com/watch?v=IQqoqUNYt_c

Edit: To clarify, we almost never used low gear all year.

Re: Experience With 6 Cim Drive train
 

CV Robotics has used single stage 6-CIM gearboxes for the last two seasons. Our experience has been great with this drive type.

While our boxes are geared for 17.5 FPS theoretical, our actual speed is ~16 FPS. We really like the increased acceleration we get, even at a higher speed of 17.5.

Electrically, we popped the thermal breaker three times this year.... twice it happened immediately after we had been in a prolonged pushing match (8-12 seconds) which is a bad idea in any case.
The other time was a fluke incident, one of the nuts on the PDB came loose and it induced a huge resistance into the system, nearly melting the plastic on the standard size power leads.

Other than that, our system remains relatively cool throughout operation with the exception of the breaker and Rear CIM plates. We have no dedicated cooling, and this year we did nothing to cool the robot between matches. However, next year we are planning on introducing some protocol to cool our main breaker and CIM's which get to 46 C/114 F occasionally.

We didn't run an on-board compressor last year, and all of our other motors were used intermittently. This gave us some extra time before the breaker thermally tripped because of reduced current demand.

Overall, we consider our 6-CIM drive to have been integral to our success the last two years. Our plan is to continue with 6-CIM unless it isn't useful for the game. Ie. If the increased acceleration/torque isn't useful next year

We recommend it :)

Re: Experience With 6 Cim Drive train
 

Does this mean you were running (at least one pair of motors) in coast mode?

I suppose there probably isn't a huge difference between 4 and 6 brakes, so it doesn't matter I guess

Re: Experience With 6 Cim Drive train
 

I'm sure you already considered them, but in the event you didn't know about them, did you look at the 11 (or 13 tooth if you were running 14 tooth CIM pinion gears) tooth gears to drop in to replace the 12 tooth pinion gears?

Re: Experience With 6 Cim Drive train
 

My bad I meant 18 and 8, I was thinking about 2 different robots

Re: Experience With 6 Cim Drive train
 

Yes, two motors were on coast.

We were running 11 tooth pinions at each of our events.

Re: Experience With 6 Cim Drive train
 

There are some interesting ideas here for dealing with main breaker trips.

I think the best solution is to gear more conservatively and enjoy the extra acceleration. For short distances, slower is faster. The last two years we have run a 6 CIM single speed drive geared for around 11-12 fps, and have never tripped the main breaker. We have used a spreadsheet to help optimize our gear ratio, and this speed seems to be a sweet spot for single speed drives. It provides great acceleration, and the current demands are low enough not to trip the main breaker. Most of the teams I have talked to about breaker problems were geared higher than 12 fps.

Re: Experience With 6 Cim Drive train
 

4159 used an amazing 6 CIM. Low of 7, high of around 17. The motors got hot during violent matches, and we tripped the breaker when we tried to push in high gear. Our low gear had an amazing amount of torque, we were able to 2-3 robots at a time no problem.

Re: Experience With 6 Cim Drive train
 

Team 716 used our first ever six cim drive and it was absolutely awesome. I couldn't ask for anything better, As the driver I didn't really see the need for the two speed so we only used a one speed, which ended up being about 15 fps. (we decided to use only the single because this game was based strictly on time so you did not want to get into a pushing match but instead wanted to zip around everyone.) It turned out though that we could still push 80% of the robots that we went against. in regards to your question, I would assume you would want to avoid an extended pushing match because it wouldn't be worth the time lost.

Re: Experience With 6 Cim Drive train
 

6 CIM drive, single speed geared for 13 FPS actual (measured) speed. 6.11:1 on 4" Colsons, if you want to do the math yourself. Treaded them for regional 2, plain for regional 1.

We had no problems tripping our breaker all season, however we did design our entire robot around preserving current. We modeled how much air our pistons might use and went with 4 plastic air tanks in order to leave the compressor offboard. Most teams only leave the compressor offboard if they have weight problems, but I think current draw is a much more important reason to consider leaving it off. To keep current draw low we used relatively few motors across the rest of the robot. Other than the drive we had just one BAG motor for the intake, one mini-CIM to drive the arm, which we partially balanced, and one mini-CIM to retract the winch, which we geared down significantly to reduce the load on the motor.

We never did take off two motors to compare the performance of a 4 vs 6 CIM drive, so all of these opinions are pretty worthless... but purely subjectively, the 6 CIM drive seemed to accelerate faster and felt more responsive than a 4 CIM drive. Interestingly, with regard to the 40 amp breaker, we found that when the 6 CIMs stalled against a heavy load, the 40 amp breakers tripped less quickly than with a 4 CIM drive. Obviously part of this is because the load is distributed across more motors, but the drive was fully stalled so each motor should have been at its max current draw. What we later realized is that with more motors, the voltage drop was greater, resulting in the motors drawing less current at stall (and also having a lower stall torque at the lower voltage). Thus, the 40 amp breakers are less of a constraint in our particular configuration with 6 CIMs than they are with 4.

Re: Experience With 6 Cim Drive train
 

This is consistent with my own observations. We had the same gearing/wheel size this year (HiGrip wheels instead of Colsons, though), and had no problems with the breaker except when the compressor was running.

Interestingly, we found that the compressor (and, by extension, any other power-consuming device on the robot) caused a twofold problem: not only does it draw current, but it lowers the effective voltage of the battery which can result in stalling a drive that would otherwise be traction-limited. This is crucially important, since if you're going to last in an extended pushing match you absolutely must be traction-limited.

Re: having less problems with the 40A drive breakers, we experienced this, too. Unfortunately, we found that unless you're exceedingly careful with current draw, at aggressive gearing going from 4 to 6 CIM SS basically results in swapping problems with the 40A breakers for problems with the main breaker. We plan to do a two-speed drive next season.

Re: Experience With 6 Cim Drive train
 

I've always read about how y'all prefer to gear more conservatively with your 6 CIM drives to abuse the acceleration boost, yet whenever I play around with acceleration and time to distance calculators I find that the extra motors become decreasingly more useful the closer you get to the "sweet spot" you have determined. At higher speeds - regardless of target distance - my calculators show that the extra motors can save a tenth of a second or so (nothing significant), and at lower speeds (especially around your sweet spot) the calculator shows improvements of a few hundredths of a second at best. Could you go into detail as to how you determine how much time you save with the extra motors to travel a set distance, and what tools you use? I feel I'm doing something wrong with the calculators I have due to the disagreements my data is showing compared to yours, but I cannot figure out what it is.

Re: Experience With 6 Cim Drive train
 

We were geared for about 10 fps with 3 CIMs throughout competition season. It was great up until we were facing alliances with high speed bots, and could not get passed them. So the sweet spot is a good sweet spot, until you are facing teams which are faster and can get in front of you faster then you can move. That is why we geared up to 15 fps for IRI, which was probably too fast for a single speed bot, but the increased speed really was needed to be competitive at a high level of play. In other years, that 10-12 sweet spot would be great, but this year with the wide open field it just was not fast enough.

Re: Experience With 6 Cim Drive train
 

I seem to recall you popping your main breaker in one of your elimination matches. Was it a main breaker blowing? Did you track down the cause of that?

Re: Experience With 6 Cim Drive train
 

We actually popped it in all 3 matches. We are pretty sure the first time was because our driver started pushing for too long, and that gearing does not do well pushing. After that, I think it had worn our breaker, because the 2 matches after that the breaker blew pretty early in the match. So we learned 2 lessons. If you pop the breaker, replace it immediately. And if you want to gear that high, it would be a good idea to have shifters. We are looking at maybe running shifters this fall, swiching between 10 fps in the sweet spot, where we never blew once, and 15+ fps for the sprints when we need to.

Re: Experience With 6 Cim Drive train
 

Bingo! This would optimize the 6 CIM drivetrain layout with the breakers allowed.

I think people are use to the 4 CIM drivetrain gears and their limits, the 6 CIMs can take a little more than what is expected. They are two different animals.

Re: Experience With 6 Cim Drive train
 

FWIW, last year with HiGrip wheels and a 120lb (including battery) robot, we were just on the very edge of traction-limited with 6 CIMs geared to 14fps (6.1:1, 4'' wheels) - i.e., we were traction limited if literally nothing else on the robot was drawing current, else we would stall the drive. Now, admittedly, we could probably have clawed back a bit of overhead with more efficient wiring, but...

Say a 150lb robot with plaction tread (COF of ~1.3 instead of ~1). So, 14 fps * (1/1.3) * (120/150) = ~8.5fps. For a comfortable amount of overhead, I don't think I'd set my low gear for anything faster than 7.5-8. Of course, you can adjust this upwards as appropriate for a lighter robot or less-frictioney wheels, but 10 fps would almost certainly be faster than I'd be comfortable with for a max-weight robot with high-traction wheels.

Re: Experience With 6 Cim Drive train
 

Which is why I recommended a 1.6 to 1.7 ratio from vex pro for thier 3 cim ballshifters as I reached same conclusion for this years game. I was thinking of it as a turbo button when that little boost is needed.

However, I think sweet spot 6 cim single speed may suffice for other years games.

Anyone push with blue nitrile geared around 12 ft/sec with 6 cims? I'm curious if increased COT impacts stall current enough to cause trips.

Re: Experience With 6 Cim Drive train
 

You are correct that the difference between 4 CIMs and 6 CIMs is not huge when geared lower. To be honest, we didn't compare the performance of different numbers of motors in great detail. The kids wanted 6 CIMs, so they got them :)

We use a spreadsheet that was originally written by Andrew Keisic on team 294. It should be here on CD, but I looked the other day and wasn't able to find it. Anyway, the spreadsheet allows you to input various drivetrain parameters, and outputs time to target distance as well as distance vs time graphs. Based on the assumption that we were using 6 CIMs, and choosing an average distance we think we would be driving during the game, we adjust the gear ratio until the time to drive that distance is minimized.

In answer to your question, if we pick a distance of 20 ft, the spreadsheet predicts it would take our robot (geared for 11 fps) 3.2 seconds to get there. Dropping down to 4 CIMs, the time increases to 4 seconds. As you said, it's not a huge difference, but perhaps more than you are seeing with your calculator.

A spreadsheet provides a method for relative comparison between drivetrain setups, but it's never going to be perfect. We also like to compare current designs with past robots. We were pretty happy with the drivetrain on our 2013 robot, so ultimately chose a gear ratio last year that would give us similar performance, even though the construction was completely different (gear drive vs chain drive). This is easy to see on the distance vs. time graphs.



One thing I would like to do is gather some real data from past robots to see how accurate the spreadsheet results are.

Re: Experience With 6 Cim Drive train
 

I see a difference of .15 secs to travel 20ft geared around 12ft/sec. Not significant like you said at these lower ratios.

But I also see a cim speed of 2850 rpm with 6 cims versus 2134 rpm with 4 cims to spin the tires of our 2014 robot in high gear in a model I built. Thus, it seems adding more cims decreases speed drop under load making the drivetrain "feel" stronger while consuming the same current? This may seem odd until you understand the cim motor efficiency curve...

http://www.usfirst.org/uploadedFiles...rves_Rev_A.pdf

Ideally, we'd always run our motors at peak efficiency instead of peak power. Only caveat is when you gear so aggressively you stall the motors where adding motors only makes the problem worse.

Re: Experience With 6 Cim Drive train
 

We had 4 CIMs and 2 Mini CIMs, geared at 5.95:1 on a AM14U with 4" wheels.

Before our regional, we ran out of 6AWG wire, and the local supplier only had 8AWG. So for around a week we ran with 8AWG and a 70A breaker. During high acceleration/deceleration or turning, with the compressor running, we did actually trip the 70A breaker a few times.

However, when we got to Hawaii (with the correct wire and breaker) we got in a number of pushing matches against teams with shifters or 6 CIMS, but we never tripped the 120A breaker.

I should note that the 70A breaker wasn't up to the same quality of the coper busman ones we have in the KoP (felt light and cheap), I suspect that it was tripping on 70A of instantaneous current, while the 120A breaker will handle 120A for quite some time. I know this is a crude measure of current draw, but it is one none the less.

Hopefully that's useful :)

Re: Experience With 6 Cim Drive train
 

On the upside, there should be huge opportunities with the new 2014 Power Distribution Board on board current monitors to detect and manage excessive power drain.

If the average of 6 cim currents is more than X amps for y seconds
turn off 2 cims ?
power back 30% ?
warn the driver ?
fire driver ?

Hope the PDB current monitoring works as well as I hope.
I could be wrong but last I heard, it was only on the 40amp outputs ?

Re: Experience With 6 Cim Drive train
 

Here is a tip for everyone in this thread who are popping their main breakers or looking to run 6 CIMs and gear fast:

1. Use lower CoF wheels.

2. Build lighter

Put down the Roughtop tread in favor of something like the VersaWheel DT or a Colson wheel. Consider constraining yourself to 100lbs instead of 120lbs. There is a reason that a team like 1625 could gear a single speed 12:64 (~17.3 fps free for those of you keeping track at home) and still T-bone like a monster this year. Lower CoF wheels and lighter weight mean pulling less current when accelerating and at stall.

Cheers, Bryan

Re: Experience With 6 Cim Drive train
 

This isn't strictly correct; a stalled motor will pull the same current regardless of the CoF of the wheels. Rather, lower CoF wheels make it harder to stall the motor in the first place.

Re: Experience With 6 Cim Drive train
 

We were 100 lbs and VersaWheel DT's at IRI, yet we still popped. If you are geared high enough to not be traction limited, Stall is Stall, so weight and CoF don't make much of a difference, other then change where traction limited is. We popped because we pushed, not during accelerating.

Re: Experience With 6 Cim Drive train
 

I think the idea is it's harder to stall with lower CoF on the wheels. However if you do stall anyways, you have the same problem.

4476 ran a 6 CIM at a 13-14 ft/s theoretical. We never popped a breaker, and I suspect it was a combo of lower friction wheels, and we put a couple of breakers on the PD board for the drive CIMS at 30A instead of 40A. The idea being that the PD breaker would trip before the main breaker would.

I'm not really sure which made a difference as both were implemented prior to testing to make sure we never blew the main breaker, but it makes sense to me that both would have had a significant factor in preventing main breaker trips.

Re: Experience With 6 Cim Drive train
 

Well yes. A stalled motor is a stalled motor. I was referring to stalling your drivetrain. I don't claim to be any sort of expert in this area and the below is oversimplified but the frictional force between the wheels and the ground = CoF x mass x gravity. If this force is greater than the force exerted by your motor on the wheel [torque at wheel / radius of wheel = force exerted] then the wheel will not turn and your drive motors will stall.

When I recommend decreasing wheel CoF and weight it is because this combination is decreasing the normal force on the robot's wheels. When you decrease the force resisting the wheel rotation such that it is less than the force attempting to turn the wheel at drivetrain stall then you are what people refer to as traction limited, meaning the drivetrain's wheels will lose traction and spin in place rather than stopping while the motors continue to try to turn.

You are exactly correct. The tips I shared are not magical, they are only directionally correct. There are other factors to consider which will effect these equations: efficiency, gear ratio, bumpers, etc. For example, when pushing another robot sometimes bumpers deform such that their weight is shifted onto your robot increasing your robot's effective mass. Sometimes the robot rocks back onto two wheels splitting the weight of the robot over only 2 wheels rather than 4. These types of things can be difficult to anticipate. I don't know your drivetrain situation (or if you are normally traction limited) so I can't comment on what might have contributed to your breaker tripping.

I do want to clarify something though. Popping the main breaker is temperature based and the cumulative result of robot actions over the course of the match. Quickly accelerating from standstill and forward / reverse slams are normal robot actions that pull large amounts of current and cumulatively heat the main breaker. This is where lower CoF wheels can provide small cumulative temperature gains (the wheel CoF determines how easily the wheel spins in place during take-off acting as a mechanical dampener mitigating the otherwise extremely high current spikes.) Using something like Omni wheels to minimize frictional losses when turning can also make a big difference. An inefficient collector or generous use of motors for auxiliary non-drivetrain actions can also be a huge factor that is often overlooked. Of course, stalling 6 CIMs will heat the breakers faster than any other individual action, and is generally the last thing that was happening before the breaker trips, and so is most frequently looked at. Pushing can often be the last large rock on the camel's back, but you can't forget all the straw you heaped up their earlier.

Hopefully this clarifies some of my thoughts on the subject.
Cheers, Bryan

Re: Experience With 6 Cim Drive train
 

The 2014 PDB does not have built in current monitoring. The 2015 PDP does.

Where did you hear that? I don't believe the PDP ever had that limitation, and it certainly doesn't now.

We ran a 6 CIM drive train, 2 speed, with theoretical speeds of ~18 ft/s and 8 ft/s. We used 8 wheel drive with versawheels. We never blew the main breaker. We played plenty of defense towards the end of the season.

We used 10 awg wire on each of the drive motors, as well as kept the wires short (PDB was mounted very near the motors). We used 4 awg wire from the battery to the breaker and PDB, but used standard 6 awg on the battery. We did not implement any software magic, but the driver new to shift to low when pushing.

Using the 2015 control system, we collected current during a match at the SCRRF fall classic. This was with rookie drivers. See http://www.chiefdelphi.com/forums/sh...&postcount=153

Re: Experience With 6 Cim Drive train
 

Man, this discussion .... if only it happened a few weeks from now rather than today. I might have had something that could show exactly (ish) where that fine line of traction limited vs breaker popping is.

EtherSim is coming...