Limiting Drivetrain Motors

[Tom Line]

I don't think that anyone can deny that FRC in general is in a bit of drive train war right now. The latitude we've been given in the last few years in motor choice and availability have made 6 cim drive trains increasingly common, with some few teams even moving to an 8 motor drive train.

That isn't a bad thing from an engineering standpoint.

Drive trains area already limited by the 120 amp breaker. Assuming the new CrossTheRoad PDB and current monitoring does what we hope it will, teams should be able to ride 'upper limit' of power while not popping their breaker.

I have to wonder, though, if we would be better served in FRC by limiting the total power output of the drivetrain. There is an argument to be made about the increasing price of multi-cim multi-speed gearboxes. A reasonable argument can also be made that the kitbot drive train has been rendered obsolete. This year, we saw an extremely brutal game. This made partially possible by the wide open field, but the high acceleration and high top-end speed that our drivetrains delivered were also responsible. A lot of robots left the field in pieces: even those of multiple-time world champions.

I think we've reached the point where it's time for FRC to consider reigning in the drive train power. I wouldn't be adverse to a max 6 cim, or even 4 cim and 2 mini-cim 'power' limit. I don't have my motor sheet in front of me to lay down the power numbers of those motors right now. What do other folks think?

[Lil' Lavery]

Here's a thread where Dr. Joe expresses a similar opinion... in 2007
http://www.chiefdelphi.com/forums/showthread.php?t=54562

I'm still not sure why the CIM limit was increased from 4 to 6.

[techtiger1]

Mr. Line,

I believe this would trend towards a lot of complaining about FIRST is suppose to be an engineering challenge why are they limiting us. I believe that COTS items will catch up quickly in the drivetrain race. This to me is one of the reasons why FRC introduced more motors, to reward innovation and the challenge of not having enough weight/time to integrate all the motors you have. That being said I myself do not take issue with the proposal if FIRST sets a rule like this, the teams must follow the rules on allowable drivetrain motors. Overall, I don't think this really makes anyone less or more competitive.

[JamesCH95]

I think that the drivetrain 'arms race' is fantastic. It forces teams to consider a serious engineering decision - how many CIMs should we put in our drivetrain? There are weight, power, traction, acceleration, lost-opportunity, and reliability factors to weigh out. There are also numerous successful drivetrains that teams can base their designs on, but the teams with a careful eye for detail and execution will still have an advantage in this facet of FRC that is being continually refined and improved.

Despite a field that seems to be narrowing, there are still numerous drive solutions that can be successful. Swerve, butterfly, 6wd, 8wd, 10+wd, octanum, etc. all have robots and teams that champion them with great success. I, personally, cannot wait to see what the next evolution of the incredible drivetrain race develops.

I really hope FIRST doesn't artificially limit the most important FRC sub-system.

[JorgeReyes]

I actually like where FIRST is right now with drivetrains. I feel there is a lot of freedom to try different drive train configurations. The majority of teams only use 2 or 4 cims in their drivetrain even with the 6 cims rule. I really like this freedom because with this freedom some teams develop very pushy robots or very fast ones that make games really fun to watch.

[Jon Stratis]

Part of me likes the idea, part of me doesn't.

In once sense, it would be nice to limit power to help preserve the robots all these teams build. This was definitely the hardest hitting year I've seen... and I know my team's robot took more damage from impacts this year than we did from falling off the tower multiple times last year!

In another... going up against stronger robots with more powerful drive trains does present an engineering challenge. It's a challenge to build robust robots. It's a challenge to design a strong drive train that avoids tripping the main breaker. It's a challenge to play any FRC game well.

Rather than setting a more-or-less arbitrary limit on "drive train power", I'd rather see the rules limit overall motors to a number reasonable for the game being played. Look at this year, for example:

6 CIM - 337W each
4 Banebots - max of 273W each
4 AndyMark 9015 - 45W each
4 Denso - 18W each
4 Bag/Mini-CIM - max 229W each
2 Window - 23W each
2 Vex 2-wire - 4W each
1 snow blower - 30W each

(Per 2014 rules and 2014 motor data sheet (http://www.usfirst.org/sites/default/files/uploadedImages/Robotics_Programs/FRC/Game_and_Season__Info/2014/2014_Motor_Information.pdf))

That's a lot of power - 4366W, if my math is correct. When I look back over previous years, our robots have never been anywhere close to that:
2014: 5 CIM, 1 RS-550 - total of 1939W
2013: 4 CIM, 2 mini-CIM, 3 AndyMark, 1 Window - total of 1964W
2012: 4 CIM, 2 RS-550, 2 FP, 1 AndyMark - total of about 2300W (I *think* the FP's were around 200W each... hard to remember)
2011: 4 CIM, 2 RS-550, 1 FP, 1 Window - total of about 2300W

I would contend that we're getting a lot more power in the rules than robots really need to be successful.

Another side of this, of course, is in the design of the game. Having game aspects that require a lot of power from the motors means you need to have more motors available. This year, we had a game where all game piece manipulation and scoring could fairly easily be done with a relatively small amount of motor power (in a large part thanks to stored energy devices like catapults that use springs or hammers that use gravity). I know we got ours for about 400W this year. Compared to previous years (600W+ in 2013 to climb the tower, 800W+ in 2012 to shoot the basketballs, 600W+ in 2011 to manipulate the tubes), this required fewer motors to accomplish, which would leave more for the drive train.

So for me, I would vote for fewer motors allowed overall, with game play designed to offer a tradeoff between power in the drive train and power for accomplishing other game tasks.

[AdamHeard]

Here's a thread where Dr. Joe expresses a similar opinion... in 2007
http://www.chiefdelphi.com/forums/showthread.php?t=54562

I'm still not sure why the CIM limit was increased from 4 to 6.

What's crazy is the power level changes since 07 have almost doubled (estimating).

[KrazyCarl92]

Personally, I could see it being cumbersome to write and enforce rules which regulate the exact mechanisms that particular motors on a robot power. Additionally, there are diminishing marginal returns to additional motors incorporate on a drive train. Adding the 3rd and 4th motors is a no-brainer. Adding the 5th and 6th motors requires proper design and a solid understanding of the drive train physics to reap significant benefits, and introduces an increased risk of popping the main breaker under certain conditions. Adding the 7th and 8th motors sees even less gains which may be inconsequential even with a proper understanding of the physics of drive trains and requires extreme caution with respect to popping the main breaker. As number of motors increases, a limit of improved functionality is approached. Where each team draws the line and what they consider "worth it" is up to them.

I would still argue that a kitbot drive train could be extremely competitive in this year's game. From scouting in Archimedes, I am aware of at least a handful of such robots.

IMO, the brutality of Aerial Assist had much more to do with game design than anything else. While the GDC may have intended the game to operate like a rube goldberg robotics demonstration like we saw in the Arizona Regional Finals or on the Weather Channel matches, it was quite clear from the get go that it would be a highly defensive game. When at most 2 robots from an alliance, and more often only 1, can interact with the game piece at a time do we expect the other partner(s) to just sit there or attempt to interfere with the opponents' offensive efforts?

Historically FIRST allowed additional CIMs beyond the previously typical 4 in 2010 (a climbing game, elevation of 18"; 5 CIMs allowed) and 2013 (another climbing game, elevation of up to 60"; 6 CIMs allowed). My understanding up through then was that the additional CIMs were included to encourage teams to pursue climbing without necessarily taking away from the typical drive train motor allotment or requiring cool PTO stuff. I would guess that the GDC likes to see teams pursuing a variety of game tasks, not ignoring them.

Then this year they also included 6 CIMs, which sort of broke any supposed support behind "climbing = more CIMs". I would've expected something along the lines of 4 CIMs + 2 MiniCIMs, still with teams using all 6 of those in the drive train as supported by the new VP and WCP gearboxes.

[asid61]

I think it's fine. The main breaker is good enough to limit power.
6 cim vs. 4 cim is kind of overblown IMO. If you have the room, put in 6. If you don't, have 4. It really is not going to affect your entire robot as long as you allocate motors to other places first. There's plenty of calculators and the like to help you decide if you will be helped by a 6 cim drive.

[tickspe15]

A reasonable argument can also be made that the kitbot drive train has been rendered obsolete.

IMO the kop drive train was more competitive this year than ever before. Although pnw is not know to have strong drive trains we had our most successful season yet running a kitbot drive. The only time we regretted that choice was in Galileo finals when we were too slow to get around defense.

With proper maitnence and lots of reinforcment the kop drive was one of the best on the field in most matches.The only downside to the drive was that we needed to replace the wheels at least once every event.

[Lil' Lavery]

I think that the drivetrain 'arms race' is fantastic. It forces teams to consider a serious engineering decision - how many CIMs should we put in our drivetrain? There are weight, power, traction, acceleration, lost-opportunity, and reliability factors to weigh out.

I think this is less and less of a question. Back when we were only allowed 4 CIMs and 2 FP motors (and maybe 1 other high power motor), absolutely. There were plenty of applications where you might want to utilize a high power motor in your manipulator design. Now the only choice really comes down to whether or not you can afford a few extra pounds for your drivetrain (especially with the new PDB and Roborio helping avoid brown outs). Scarcity/lost-opportunity is no longer a concern with 6-CIMs and quite a few other high-power 500 and 700-series motors available to teams.

[Chris is me]

One thing to consider is the context in which the motor rules of 2012, and then later 2013 came about.

In 2011, you were allowed 4 CIMs, 1 FP, 4 BB, 4 Window, and that's about it. This essentially forced teams to use Banebots motors. I'm pretty sure the FPs sold out that year? This was also the year with defective 775s, 2+ week lead times from Banebots, and generally poor service. People didn't like that we were all but forced to go through one supplier.

So in 2012, more options were introduced. We were allowed 4 CIMs, 2 FPs, 4 Banebots, 4 AM motors, 4 Window, past KoP motors, and there was this weird deal with auto junkyards no one used. The intent wasn't to increase available power to teams as much as it was to not force them to use a particular supplier for their "medium power" 200ish watt motors.

In 2013, Vex began making FRC mechanical parts, so the MiniCIM / BAG were added in a similar manner to other motors: you got up to 4 of them. I suspect climbing motivated the use of 6 CIMs. I assume the GDC saw teams using 6 CIMs without climbing, didn't see drivetrains destroying other drivetrains much, and decided it wouldn't be a bad thing for 2014 either.

Basically, I'm contesting the assumption that the GDC opening up the motor rules is about them wanting us to have more mechanical power. I think they just want us to have options as to how we drive mechanisms. In the spirit of that, a power limit would keep these options open but limit the overall power . Not saying I support or oppose it, but that's one solution to the problem without backpedaling on why I feel these changes were made in the first place.

[AllenGregoryIV]

I'm not sure we need to limit motor power. The main breaker does an okay job but the real limiter is traction. As long as the carpet and weight limit are in place there is only so much power you can physically transfer to the ground.

We ran 8 motors this year. We never popped our main breaker and one of the main reasons that I would continue doing it is that are motors actually stayed much colder than in the past.

[Max Boord]

I see this as limiting innovation. I can guarentee teams are working hard right now to create 6 cim swerve and tex-coast drives wich would likley never be created if there was a rule created banning 6 cim drives.

Also, if your robot had a PTO gearbox do the motors in it count as drive train motors or whatever else the gearbox is driving?

[cbale2000]

We used a 6 motor drive train (4 CIMs, 2 Mini-Bike Motors) back in 2006 on a similarly open field with no bumpers on the robot. We also built the frame out of solid sheets of 3/16" aluminum, needless to say we had no durability issues with the frame.

Rules that try to limit drive motors are really just limiting mechanism options, and rules putting a cap on drive system power will make inspections more complex, and likely longer.

The game animation for as long as I've been in FIRST has included the line "Robots should be built robustly", IMO teams simply need to design with robot durability in mind, otherwise the exciting contact sport that is FRC eventually becomes a dance recital.

[Billfred]

I don't think the kitbot is obsolete by the available power, but it does require a little work to tap the power. We did switch in the AndyMark 3CIM4U gearboxes ($150 for the pair, if I recall) and ran our underweight robot just fine all season. Total BOM on the change would probably be around $260 with the two extra CIMs and a pair of speed controllers (which IFI has a PDV for if you want to split hairs). If a sub-$300 parts order is causing major insomnia, I'd question whether the team was really prepared to compete in FRC.

The other notion: 6-CIM setups have fewer parts (and fewer small moving parts) compared to a shifting design. Could this be FIRST's subtle helping hand to ensure drivetrains stay mobile?

That said, if FIRST was worried about it I say limit teams to five CIMs. Teams will either do without, shift gears, or learn a thing or two about matching motors to party like it's 2004.

[AllenGregoryIV]

The other notion: 6-CIM setups have fewer parts (and fewer small moving parts) compared to a shifting design. Could this be FIRST's subtle helping hand to ensure drivetrains stay mobile?


I don't think this is FIRST's plan but I do think it is an advantage. I've never been on a team that has used shifting gearboxes in competition. Our setup this year shifted the wheels to get speed reductions but we haven't used something that can fail in the same way as your standard two speed gearbox.

[colin340]

I would hate to see the arms race end, fast robots and harder hit are way more fun for all parties, other then rookies.

[Andrew Schreiber]

I would hate to see the arms race end, fast robots and harder hit are way more fun for all parties, other then rookies.

And anyone trying to actually play the game. It gets old going out and spending most of the match being smashed into by teams that are incapable of playing the game.

[colin340]

And anyone trying to actually play the game. It gets old going out and spending most of the match being smashed into by teams that are incapable of playing the game.

Fair point, but this year we got called for hitting the defense bots back too hard. Teams that are blockading / pinning a partner should design for 13 fps hits or get out the way.

i'm sick of playing tea party games / soccer.

[BBray_T1296]

IMHO, it was very obvious day one that high speed defense would be prevalent.

[adciv]

I see more than 4 cims being necessary as it limited the arm/endeffector designs. If there needs to be a limit on the drive systems, this could be accomplished by limiting the drive system to four CIMs.

That said, our main issue this year was teams entering our frame perimiter. We have some gashes (1ft above the bumpers) in our 1/8th(?) aluminum from other robots.

[Orion.DeYoe]

I don't think that anyone can deny that FRC in general is in a bit of drive train war right now. The latitude we've been given in the last few years in motor choice and availability have made 6 cim drive trains increasingly common, with some few teams even moving to an 8 motor drive train.

That isn't a bad thing from an engineering standpoint.

Drive trains area already limited by the 120 amp breaker. Assuming the new CrossTheRoad PDB and current monitoring does what we hope it will, teams should be able to ride 'upper limit' of power while not popping their breaker.

I have to wonder, though, if we would be better served in FRC by limiting the total power output of the drivetrain. There is an argument to be made about the increasing price of multi-cim multi-speed gearboxes. A reasonable argument can also be made that the kitbot drive train has been rendered obsolete. This year, we saw an extremely brutal game. This made partially possible by the wide open field, but the high acceleration and high top-end speed that our drivetrains delivered were also responsible. A lot of robots left the field in pieces: even those of multiple-time world champions.

I think we've reached the point where it's time for FRC to consider reigning in the drive train power. I wouldn't be adverse to a max 6 cim, or even 4 cim and 2 mini-cim 'power' limit. I don't have my motor sheet in front of me to lay down the power numbers of those motors right now. What do other folks think?

Absolutely not.
This is an engineering competition. Teams try to find mechanism configurations that give them a competitive edge. If 6-CIMs are "breaking the game" then it's because too many teams are holding to the old 4-CIM way. Stronger drivetrains encourage more robust designs which teaches better engineering practices.
That being said, for the past two years we stuck with 4 CIMs on our drivetrain and never had a problem with being pushed around by stronger drivetrains.

[FrankJ]

Realize it an engineering design competition with limits. You don't get to choose your battery. You have a weight limit. Limiting drive motors would just be another limit. I am sort of for it. Or maybe we could go back to regolith? Traction limited drive systems: Oh yeah.

[adciv]

If 6-CIMs are "breaking the game" then it's because too many teams are holding to the old 4-CIM way. Stronger drivetrains encourage more robust designs which teaches better engineering practices.

Other possibility: The game becomes about who has the strongest drivetrain to the exclusion of all else.

To use the 2011-2012 FTC game Bowled Over for similarity, the game became all about one aspect: Putting one ball in a crate and lifting it as high as possible. This was not the intent of the game. The GDC did not realize FTC robots would be able to go over seven feet high, much less seventeen feet.

It is possible for changes in the rules to "break the game" by making it all about one aspect. You can't teach better engineering practices by removing the tradeoffs that come with balance. And "robust designs" is a different issue entirely. Robots getting damaged/destroyed is not the intent. FIRST is not supposed to be Battle Bots.

[magnets]

To use the 2011-2012 FTC game Bowled Over for similarity, the game became all about one aspect: Putting one ball in a crate and lifting it as high as possible. This was not the intent of the game. The GDC did not realize FTC robots would be able to go over seven feet high, much less seventeen feet.


Do you have a video of a high lifter? I can't find many FTC videos on the internet

[pntbll1313]

Do you have a video of a high lifter? I can't find many FTC videos on the internet

Here's a pretty cool match with high lifters:
http://www.youtube.com/watch?v=imuLGW4Wf9s

[adciv]

Here's a picture (http://firsttechchallenge.blogspot.com/2012/01/new-high-score.html#!/2012/01/new-high-score.html) of the two robots that started the Arms Race. The taller of the two (on the left) was merely 9ft tall. The US was sold out of 1" square tubing before the end of that qualifier.

[RyanShoff]

A modern swerve drive takes 8 motors just for the drivetrain. I would be extremely disappointed if rule changes killed a whole class of drivetrain.

Last year we had 13 motors and a compressor. More motors are more inspirational.

[Lil' Lavery]

I see this as limiting innovation. I can guarentee teams are working hard right now to create 6 cim swerve and tex-coast drives wich would likley never be created if there was a rule created banning 6 cim drives.
Do you not think innovation can be accomplished with fewer motors, as well? Are the only innovations left in FRC drivetrains more powerful or refined versions of what has come before?

A modern swerve drive takes 8 motors just for the drivetrain. I would be extremely disappointed if rule changes killed a whole class of drivetrain.
I doubt there would be any limitations on motors used to steer, or that otherwise don't actually provide any power to the wheels. Also, there have been plenty of swerve variants that have used fewer than 8 motors.

Last year we had 13 motors and a compressor. More motors are more inspirational.
Why are more motors more inspirational? Isn't finding a way to accomplish a task despite limitations also an inspirational activity?


Note: I don't necessarily want a restriction on drive power, I just find some of the arguments being used against it to be rather peculiar.

[NotInControl]

I don't think that anyone can deny that FRC in general is in a bit of drive train war right now. The latitude we've been given in the last few years in motor choice and availability have made 6 cim drive trains increasingly common, with some few teams even moving to an 8 motor drive train.

That isn't a bad thing from an engineering standpoint.

Drive trains area already limited by the 120 amp breaker. Assuming the new CrossTheRoad PDB and current monitoring does what we hope it will, teams should be able to ride 'upper limit' of power while not popping their breaker.

I have to wonder, though, if we would be better served in FRC by limiting the total power output of the drivetrain. There is an argument to be made about the increasing price of multi-cim multi-speed gearboxes. A reasonable argument can also be made that the kitbot drive train has been rendered obsolete. This year, we saw an extremely brutal game. This made partially possible by the wide open field, but the high acceleration and high top-end speed that our drivetrains delivered were also responsible. A lot of robots left the field in pieces: even those of multiple-time world champions.

I think we've reached the point where it's time for FRC to consider reigning in the drive train power. I wouldn't be adverse to a max 6 cim, or even 4 cim and 2 mini-cim 'power' limit. I don't have my motor sheet in front of me to lay down the power numbers of those motors right now. What do other folks think?


I personally would like to see the rules more relaxed. I would rather the GDC do more of "I wonder what teams will come up with if we allow more of this..." rather than preventing what teams can create.

But playing devils advocate: Assuming the rule you described was implemented, how would one begin to regulate this rule? Drivetrain output power is determined by gear ratio, motor configuration, motor load, etc. All of these variables are engineering parameters that teams can choose based on their desires. To ensure robots are under the maximum power usage, the inspectors would need to measure or calculate power draw while the robot was under some worst case driving load to show it never pulls x much power. Is this even possible in the pits? Wouldn't this also mean that you would need a fully functioning/driving robot before you were able to pass inspection? Furthermore, unless the inspectors had their own current or power meters that they could connect to your robot while you were doing this demo, you would also be forcing every team to use the CAN interface. The inability to regulate this rule, my just be a reason why it can not be a rule.

In addition, the PDP we are currently using for Alpha Testing provides current monitoring for each channel on the PDP (1-16), not for the entire system. I suppose one could measure all channels, and then sum them up to provide an estimated system current draw.

However, I think I understand why you are thinking of this approach - to be a uniform solution to prevent main breaker trips, correct?
The 120Amp main breaker is not limiting at all. It takes a long time to trip and can handle 500+% of 120 amps for seconds before tripping under the right condition. The main breaker is a thermal device, not a current device. It trips after passing a certain temperature. Large current surges is just one way to raise the temperature of the device, however it is completely true that if you took a heat gun to the main breaker it would trip even under no current load. The proper way to prevent the main breaker from tripping is to design motors with the proper gearing ratios to prevent such cases.

However, If I were to design an automated control system to help prevent tripping the main breaker in 2015, this is how I would do it:
Since I know the main breaker trips based on temperature, that is the variable I want to measure. In control systems, when you have a system that is controlled by one variable (heat in this case), but you measure something else (current in this case) and use that to estimate the other, that is called an indirect measurement. This can leads to all sorts of trouble like making the wrong decision. When I am designing any new control systems, I want to directly measure all of the control variables, only if it is impossible for some reason (i.e. against the rules) then will I venture down the indirect measurement path.

I would use a thermocouple mounted to the power terminal of the main breaker to monitor the terminals temperature. When the temperature of the terminal goes above some threshold (based on spec sheet, or team experimental data) I would then warn the driver (via driverstation/lights on robot etc.) that the main breaker is approaching the tripping point. I could then automatically enter some "reduced power mode" of the robot where I would start scaling back the max power to the most power hungry systems determined by the max current draws measured on the PDP. For example, I could reduce the max output of the drivetrain to 75% while in reduced power mode, and stop the motor all together when I detect a stall condition (large current surge for some duration of time on some channel). I would keep doing this, until the temperature drops down below another threshold where I could then re-enter "normal power mode" and let the robot rip.

For added effect, I would mount the main breaker on top of a fan, and kick the fan on during reduced power mode to help it cool down faster. Or leave it on at all times to help prevent going into reduced power mode in the first place.

The system would also have the ability to be disabled by any of the drivers by pressing a button in real time.

Why would I do this over just measuring current? Well the main breaker is a thermal device. If I were measuring current, all I could determine is that the the current spiked over some threshold. This is not an indication that the breaker is approaching its trip point. The breaker can handle large loads for many seconds and even minutes depending on the conditions. The problem is that the time to trip is not deterministic. It can be milliseconds, seconds, or even minutes. In a match, I want to stay competitive as long as possible, for example staying in a pushing match for as long as possible. Prematurely reducing/disabling power to robot systems because I detected a current surge is very overly cautions and can reduce my competitiveness. The last thing I want to do is lose an elimination match because I disabled/reduced power to certain robot components because I thought the main breaker might blow, especially when it was no where near the tripping point. Measuring temp gives me the best information to make the best decision at that moment in time, I can let the robot rip it up for as long as I can until the temp of the main breaker reaches a worrisome point. I don't have to worry about prematurely reducing my systems. I have more useful information measuring temp and so I can make smarter decisions. I can also allow the robot recover back to full potential and rip it up again, once the temp drops down keeping my competitiveness, and the full advantage of my robot.

Remember these systems don't guarantee that the breaker will trip, they just inform you that the probability of the breaker tripping is higher. In a regional/district winning match, I would probably let the robot approach the trip rather than prematurely disabling/reducing power to critical systems. This is just me, I am more of a gambler and I trust the systems we design as a team. This is especially true in the last 30 seconds of a match, where I probably need my robot to push its limits to the end. I'd rather take the chance and hope it doesn't trip during a critical match, rather than reduce the capability of my robot where I can no longer be as effective/competitive. Its a trade off, its a gamble.

One could argue "couldn't you just use the PDP and average the current surge over some amount of time to help increase the probability that the main breaker is approaching the trip point.?" Yes you can, however this is still an indirect measurement. If measuring the temp of the main breaker is not feasible for some reason in 2015, this is the next best approach, and the one I would employ. It still has the problem that I do not know if the breaker is warm or not when the current surge is detected, but it is way better than nothing.

All of this doesn't replace good drive train design. These are just warning systems and can provide the drivers useful information in a match. The best defense against main breaker trips is to design appropriate drives in the first place. 2 speed gearboxes, ramping up your drive commands, and knowing when to switch to low gear can get you the 99% solution.

Main Breaker manufacture Spec PDF is attached

Hope this helps,
Kevin

[FrankJ]

Or you could just mount the main switch on a good heat sink & put a fan on it?

[Jon Stratis]

I personally would like to see the rules more relaxed. I would rather the GDC do more of "I wonder what teams will come up with if we allow more of this..." rather than preventing what teams can create.

But playing devils advocate: Assuming the rule you described was implemented, how would one begin to regulate this rule? Drivetrain output power is determined by gear ratio, motor configuration, motor load, etc. All of these variables are engineering parameters that teams can choose based on their desires. To ensure robots are under the maximum power usage, the inspectors would need to measure or calculate power draw while the robot was under some worst case driving load to show it never pulls x much power. Is this even possible in the pits? Wouldn't this also mean that you would need a fully functioning/driving robot before you were able to pass inspection? Furthermore, unless the inspectors had their own current or power meters that they could connect to your robot while you were doing this demo, you would also be forcing every team to use the CAN interface. The inability to regulate this rule, my just be a reason why it can not be a rule.


Without getting into the big long analysis of how to (prevent) trip the main breaker, I wanted to address this from an inspection perspective. For at least the past few years, FIRST has provided a Motor Performance Data Sheet (http://www3.usfirst.org/sites/default/files/uploadedImages/Robotics_Programs/FRC/Game_and_Season__Info/2014/2014_Motor_Information.pdf) which contains information on most of the motors we're allowed to use, and probably all of the motors we're allowed that you would want providing locomotive power in your drive train.

Why should we measure output power when we can measure max motor power instead? Sum up the max power for each motor on the drive train and you're done. That leaves us with a practical upper limit on speed and power output in a drive train without getting into all of the specifics you mention. Further, with appropriate limits we can pass most teams without question quickly and easily. "4 CIMs on the drive train (like 75%+ of all teams)? You're good to go!" "4 CIMs, 2 mini-CIMs, and 2 775s? We'll have to do the math on that one..." And the best part... it doesn't require any special skills or knowledge from the inspectors in determining if it's legal - just some basic addition.

[Andrew Schreiber]

Without getting into the big long analysis of how to (prevent) trip the main breaker, I wanted to address this from an inspection perspective. For at least the past few years, FIRST has provided a Motor Performance Data Sheet (http://www3.usfirst.org/sites/default/files/uploadedImages/Robotics_Programs/FRC/Game_and_Season__Info/2014/2014_Motor_Information.pdf) which contains information on most of the motors we're allowed to use, and probably all of the motors we're allowed that you would want providing locomotive power in your drive train.

Why should we measure output power when we can measure max motor power instead? Sum up the max power for each motor on the drive train and you're done. That leaves us with a practical upper limit on speed and power output in a drive train without getting into all of the specifics you mention. Further, with appropriate limits we can pass most teams without question quickly and easily. "4 CIMs on the drive train (like 75%+ of all teams)? You're good to go!" "4 CIMs, 2 mini-CIMs, and 2 775s? We'll have to do the math on that one..." And the best part... it doesn't require any special skills or knowledge from the inspectors in determining if it's legal - just some basic addition.

But what motors count? If I do a steered wheel system do the steering wheels count for this determination?

Truth, adding arbitrary design constraints like that just seems the wrong approach. I assert that with good game/field design it should be possible to minimize the impact of the increasing motor power. Make it so it's more worth my time to play the game than to ram others. Don't let me accelerate the length of the field into another bot by dividing the field up.

2014 was rough for reasons unrelated to the motor power. Most folks who were doing the worst of the ramming likely only had 4 motors in their DT anyway. It was the ability to accelerate cross field and overworked refs that caused the plethora of ramming issues.

[Chris is me]

I think the assumption being made by a lot of posters in this thread is that 6 CIM drives are a large competitive advantage. People have stressed this to the point of saying the Kit of Parts is "obsolete" because it has a 4 CIM drive.

While a 6 CIM drive definitely has some benefits, they are not magic. 6 CIMs do not increase your pushing force when you are traction limited. While most single speeds aren't geared to run indefinitely under traction-limited load (pushing against a wall), they are usually geared to be traction limited at SOME point before stall. Thus the pushing force "cap" for robots isn't determined by the number of motors.

Acceleration is trickier, as it's very hard to model several dynamic factors in play to make a general case situation for all robots.

Honestly, I think tons of non-top teams faced extreme defense for the first time this year. Their robots got damaged, they want something easy to blame, so the first guess was more CIMs in opponent drives. The game design sucked and we're scapegoating the motors.

[AllenGregoryIV]

Honestly, I think tons of non-top teams faced extreme defense for the first time this year. Their robots got damaged, they want something easy to blame, so the first guess was more CIMs in opponent drives. The game design sucked and we're scapegoating the motors.

I agree, motor limit or not, high speed ramming would be in issue in this game. We have bumpers for a reason, hard clean hits between two robots that can take it is very entertaining and have been a part of most FRC competitions over the past two decades. Finding game designs that limit destructive actions is hard but should be part of every game design.

[Tungrus]

"More is better"? A good engineering is doing more with less (no, not Target's catch phrase). It would be awesome if some team can design an efficient and powerful drive train without adding more hardware.

[asid61]

Without getting into the big long analysis of how to (prevent) trip the main breaker, I wanted to address this from an inspection perspective. For at least the past few years, FIRST has provided a Motor Performance Data Sheet (http://www3.usfirst.org/sites/default/files/uploadedImages/Robotics_Programs/FRC/Game_and_Season__Info/2014/2014_Motor_Information.pdf) which contains information on most of the motors we're allowed to use, and probably all of the motors we're allowed that you would want providing locomotive power in your drive train.

Why should we measure output power when we can measure max motor power instead? Sum up the max power for each motor on the drive train and you're done. That leaves us with a practical upper limit on speed and power output in a drive train without getting into all of the specifics you mention. Further, with appropriate limits we can pass most teams without question quickly and easily. "4 CIMs on the drive train (like 75%+ of all teams)? You're good to go!" "4 CIMs, 2 mini-CIMs, and 2 775s? We'll have to do the math on that one..." And the best part... it doesn't require any special skills or knowledge from the inspectors in determining if it's legal - just some basic addition.
I agree. If motors were ever limited, I would want to do it by maximum power.

[Richard Wallace]

I like motors. :]

If it ever becomes necessary to limit robot mobility, FIRST should prohibit wheels that contact the playing field surface.

----

Oh, and @the earlier comment comparing limited mobility games to tea parties / soccer: there's a guy named Dempsey (http://www.sportsworldnews.com/articles/14903/20140618/clint-dempsey-nose-broken-video-usa-star-will-wear-mask-for-rest-of-world-cup.htm) who probably would not agree that soccer is anything like a tea party.

[yarden.saa]

tradeoffs are part of the engineering proccess. In previous years we had to calculate what motor we need for any mechanism (not only the drive train).
In this year most of the teams said, lets put cims/mini cims without even try another motors. The game this year was really easy. the task of throwing the ball isnt easy but when you have 6 cims and 4 minicims, you don't need tradeoffs in the drivetrain motors in order to get a good shooter/launcher. Most of the teams had 2/3/4 cims/mini cims in their shooter, but we could get the same result with less powerful motors with smarter mechanisms(you can find very few examples who did this, look at 254 shooter with only 2 small motors).
Some will say that more power is better but it is better only when it fits the game. Aerial assist is one of the easiest games because you only need to throw a ball, but has the highest power available for teams ever.
It doesn't make sense:confused:

[JamesCH95]

Lil'Lavery brings up a good point - it is inspirational to 'do more with less' and a lot of anti-power-limiting sentiment is based on flawed logic. However, I think that the 'enough rope to hang yourself with' philosophy is a better approximation of real-life engineering than 'try to do more with less.' I think that it's far easier to terminally screw up a project by getting too ambitious and overspending/over-promising than it is to exceed expectations.

ChrisIsMe and Andrew Schriber both hit the nail on the head - poor game design and (related) overworked refs lead to the serious amount of high-speed ramming we saw this year. Heck, our 4-cim robot managed to shear its deck (http://i.imgur.com/ihi302I.jpg) during a bumper-to-bumper high-speed hit. Dropping the motor count down to 4 cims again wouldn't have prevented this from occurring.

I'll draw a parallel: F1 racing. Every few years the allowed engine displacement is reduced (http://en.wikipedia.org/wiki/Formula_One_engines#Engine_specification_by_era), or the amount of time an engine must be in service is increased. These rules are designed to limit the power available to F1 teams, but guess what? Lap times generally just keep dropping, and dropping.... (http://www.motorsportsetc.com/info/spd_mon.htm) So I don't think that dialing back on available motors will really solve the problem of 'robots that are too fast' unless our motor selection is reduced to the days of yore when 3/8 drill motors ruled the land. In 2013 no one complained about having too many motors, nor was there carnage on the field from high-speed hits despite having essentially the same motor selection available. The differences? Protected scoring and loading positions, non-open fields, and a scoring system that didn't rely on multiple refs poking through multiple menus to enter in scoring actions on their input consoles (taking time away from actually reffing the match).

Reducing motor count, barring severe restrictions, won't reduce high-speed impact damage. 4-cim robots are more than capable of causing severe damage with open-field bumper-to-bumper hits. Good game design will reduce high speed impact damage. See 2013, where defense was more cat-and-mouse than WWF smackdown, despite having essentially the same available motors.

Fair point, but this year we got called for hitting the defense bots back too hard. Teams that are blockading / pinning a partner should design for 13 fps hits or get out the way.

i'm sick of playing tea party games / soccer.

Clearly you've never played soccer at a serious competitive level.

I like motors. :]

If it ever becomes necessary to limit robot mobility, FIRST should prohibit wheels that contact the playing field surface.

----

Oh, and @the earlier comment comparing limited mobility games to tea parties / soccer: there's a guy named Dempsey (http://www.sportsworldnews.com/articles/14903/20140618/clint-dempsey-nose-broken-video-usa-star-will-wear-mask-for-rest-of-world-cup.htm) who probably would not agree that soccer is anything like a tea party.

None of these guys (http://en.wikipedia.org/wiki/List_of_association_footballers_who_died_while_pla ying) would agree either.

/threadjack

[qnetjoe]

I think it is important to take a step back and look at basis/perspective on this, most of us come from team that have a good amount of engineering resources/experience.

Opening up the motor rules really helped middle to lower level teams reuse older parts and required less engineering expertise to field better bots. I know a lot of those teams that refuse to use to window motors (and some even the BB motors) because it is "too hard to" compared to me who has a broach for the window motor spline in my garage.

It is important that all of us realize that FIRST is more about helping the lesser teams do more with less support/resources, hence the push in 3D printing and lessening of the rules. Just like in business, regulations/rule changes do not affect the upper echelon teams as much since they have resources to work around them, it is the the small teams that take the blunt of it.

Just to kill some parallels, in F1 the top speed of the cars is what they seek to limit by the rules and that has stayed rather close in the last 15 years or so. Lap times have been going down due to advancements in suspension and handling. The reason they claim to need to limit top speed is due to safety.

If FIRST was going to do anything it would be to lower the rating on the main circuit breaker. That would limit the max power that could be delivered without some crazy rule change.

Just my two cents

[jman4747]

I do think robot damage is more of a game design problem the field was so open. When's the last time any robot could go anywhere at any time (excluding auto)?

I am however indifferent to a limit on drive train power or motor usage. The worst thing to do by far would be to reduce the limit on total allowed motors on the robot. Most of the innovations in robot design come from game specific systems, tank drive trains sporting 6cim inputs usually have few functional differences from 4cim drives.

[JamesCH95]

Just to kill some parallels, in F1 the top speed of the cars is what they seek to limit by the rules and that has stayed rather close in the last 15 years or so. Lap times have been going down due to advancements in suspension and handling. The reason they claim to need to limit top speed is due to safety.

I won't disagree that F1 lap times have been improved primarily by suspension and handling, but it doesn't negate the parallel. If motor availability (engine displacement) is reduced then teams will find other ways to make their robots (cars) just as fast as they were, like multi-speed automatic transmissions (improvements in suspension, brakes, and tires). This fits in nicely with your point - the restriction won't slow down the higher-end teams who can devote resources to making more advanced transmissions (develop suspension, tires, brakes) but it will hurt middle and bottom tier teams who do not have the resources to devote to these efforts.

[pfreivald]

I like motors. :]

If it ever becomes necessary to limit robot mobility, FIRST should prohibit wheels that contact the playing field surface.

Walker-bots FTW! I would love to see this one year, just to watch peoples' brains explode at kickoff.

-------

On-topic, the destructive nature of this year's game had every bit as much to do with a completely open field as it did with drive trains. Those of us from the pre-bumpers era, I think, widened our eyes and thought, "oh, it's back to that, is it?" when we saw the game. Imagine how differently this would have played out were their barriers (Rebound Rumble), horizontal poles, humps (Breakaway), or the like dividing up the field....

[mwmac]

I won't disagree that F1 lap times have been improved primarily by suspension and handling, but it doesn't negate the parallel. If motor availability (engine displacement) is reduced then teams will find other ways to make their robots (cars) just as fast as they were, like multi-speed automatic transmissions (improvements in suspension, brakes, and tires). This fits in nicely with your point - the restriction won't slow down the higher-end teams who can devote resources to making more advanced transmissions (develop suspension, tires, brakes) but it will hurt middle and bottom tier teams who do not have the resources to devote to these efforts.

Since F1 was brought up and totally unrelated to the op's topic, lap times have been dropping primarily due to advances in aerodynamic efficiency. This is why the FIA has been increasing limitations on the size/extent of aero surfaces on F1 race cars.

[asid61]

Or you could just mount the main switch on a good heat sink & put a fan on it?

Can you do that? That seems kind of cheap...
At that point, you might as well tack on another few pounds to add in a whole high power LED cooling system.