Limiting Drivetrain Motors

[tickspe15]

Originally Posted by Tom Line

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]

Originally Posted by 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.

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]

Originally Posted by Billfred

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]

Originally Posted by 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.

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]

Originally Posted by Andrew Schreiber

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.

[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]

Originally Posted by Chris is me

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.

[Lil' Lavery]

Originally Posted by 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.

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?

Originally Posted by 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.

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.

Originally Posted by RyanShoff

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.