Motor Restrictions

[Michael_Puckett]

Perhaps this has been asked multiple times, but as I just started helping out my old high school's FRC team this year as a mentor I've come up with a bit of a question. Our team is looking at a very simple solution to a problem, but we're potentially being hamstrung by the infamous motor legality issue. We're looking at an actuator with an included motor that would be exactly what we need, but due to the rules we may not be able to use it and might have to essentially build our own actuator, which only adds time and complexity to our already fairly new team.

All that said, my basic question is what is the purpose behind limiting what motors teams can use? They are already limited by the overall price restriction ($400 max), power draw (PDB has 40 amp max on a single channel), and voltage (12V limit for motors), which effectively limits high power motors fairly effectively. I can understand limiting the number of higher power motors as is currently done with CIMs, but this rule could be rewritten to state "only X number of motors over Y watts" or something like that.

Restricting small motors is what seems so odd. I've taken apart a printer and found several small motors that could be useful for things, but can't use them because they aren't automotive (per 2015 rules at least). I can use a large number of powerful automotive motors all over the robot, but not one smaller, less powerful one just because it hasn't been used in an automotive application? Similarly, if I want to tailor motor selection based on rpm and torque I'm limited to trying to find a gearbox that will interface with one of the approved motors as opposed to just sourcing a motor that does what I want to start with. Along those lines, a lot of the approved motors don't have output shafts that are easy to deal with. Trying to use a tiny 1/8" round output shaft to drive anything larger is difficult. I almost need to grind a flat onto the shaft to make it D shaped so I have anything I can key into.

I understand that this late in the game I don't expect the motor rules to magically change and get more open, but I'd like to encourage those who write the rules to consider loosening the restrictions for future years. Instead of our team determining how to mount and use the components we want, we're spending time trying to figure out if they're legal to begin with or could be made legal. We're hesitant to buy anything with our limited budget since there's a chance we could get turned away at tech. Instead of letting the kids branch out and try new options, they're stuck reading the rules to see if they can use any of their ideas. That's not what FIRST is about. FIRST is about letting kids turn their imaginations into real physical form. Instead of part number limitations I'd encourage the rule writers to limit motors by output or other specs, similar to what is done with solenoids (max watts, limited stroke, etc.). Maybe have an RPM and torque cap for motors at 12V and 40A, or some curve that relates the two (ex. a 200 rpm motor can have more torque than a 10,000 rpm motor, some kind of inverse relationship between the two). Admittedly, testing and verification of the motors would be the next challenge, but perhaps this could be solved by requiring teams to have a data sheet for each motor they use submitted at the time of tech.

[IronicDeadBird]

It is all basically about leveling the playing field. Most motors they allow fall into a category and each category has roughly equivalent utility and pricing. This prevents "Super teams" (teams that were bitten by a radio active NASA mentor)* from getting hardware that completely outclasses new teams.
The other points you brought up are absolutely solid, and I hope that the GDC is working or has a group working on refining these building constraints that generally stay consistent year to year... Minus the unlimited motor thing. What I find surprising is that every year the pool of motors should expand to include more options providing more versatility in builds but it doesn't.
Then again the mentality of adding versatility through expanding an options pool is a video game thing not a robot thing...

[Bob Steele]

I found that this year the motor selection was opened up much more than in the past. The only stipulation is that the motors had to be from the list.

Our only limitation was 6 of the large "CIM" like motors.

All of the other motors were unlimited ...you pick 'em.

This is a nice step. Perhaps next year it may be
"you pick 'em" from the list with no limitation on CIMS.

A team can certainly get the same "punch" from doing multiple motors as with a CIM if they wish.

I think that the limitation is really that the Power Distribution Board has a limited number of slots and breakers.

Of course the practical limitation is the battery and keeping the control system functioning in the match.

I can see giving a list of motors. It prevents teams from taking advantage of some special motor that they found...that no one else can find...

I would hazard a guess that perhaps next year we might be able to ask to put certain motors on the list as 'equivalent' motors. This would be similar to what was done with batteries last year.

This is a far cry from former years when we were limited to 4 CIMS and had limits on all of the other motors too...

Good change this year.

[Michael_Puckett]

Originally Posted by Bob Steele

...I can see giving a list of motors. It prevents teams from taking advantage of some special motor that they found...that no one else can find...

I think this is addressed by the other rules already in effect though, namely cost and available power. There might have to be one other stipulation that every motor has to be costed, regardless of how it was acquired (as this might be a way to bypass the $400 rule if someone was really looking for loopholes). Also, maybe along the lines of the datasheet idea where each team would have to post datasheets for any motor they use. Perhaps this could be made public as well as opposed to just a tech item.

I guess I'm of the mindset that if one team can find a motor, any other team should be able to find that motor with some digging. Being restricted to 12V and 40A effectively limits your output potential, though those are still scary numbers in their own right (think car starter motor).

The current "any automotive door/window/wiper/seat motor" is a step in the right direction, but still seems oddly specific. Why limit it to automotive applications? If they are trying to limit power then why not just say that? If they are trying to limit cost, they could just do that as well (no motor can cost more than X dollars, which could be different than the $400 general component limit). I'm sure there's probably some ridiculous automotive motor out there that has the power to shut a 500 pound armored door that would technically be legal by the current rule set, but I'll admit I'm exaggerating a bit on purpose. I guess what I'm trying to get at is that the current wording just seems too vague. It sounds like they're trying to open it up, but I'd just like to know what they were getting at when then decided to allow "automotive" motors.

[Jon Stratis]

The limitation to any "automotive..." Motor has a historical basis. For years various window and door motors have been in the Kit of Parts, and even the common window motor everyone knows these days has had different model numbers in the past (should it be illegal just because the model number changed?). A few years ago FIRST opened it up with a deal with the Automotive Recyclers Association (I think that's what it's called... Please correct me if I got that wrong), and allowed window, Door etc motors that were provided from the ARA. This opened it up to a huge range of motors. Now, FIRST has simply removed the ARA restriction.

A long history with specific motors and types of motors tends to have its own momentum with current and future rules. That's not to say that it can't change, but FIRST will probably continue to move slowly on opening up the rules in order to ensure fairness for all and keep us from creating an "arms race" for the most powerful motors. After all, the drive train power race we've seen the past couple of years has been scary enough!

[Bob Steele]

FIRST has been supported by the automotive industry from the very beginning. It may have slacked abit but they still support many teams. I believe that the "automotive" designation is due to the motors that have been contributed to teams over the years. They want to include those and they are primarily automotive motors... examples of motors that we have used include van door motors, window motors, etc. (Jon beat me to this ... see above for a better explanation)

It is good to see newer teams asking these questions. Those of us that have been around a long time see the last few years as really loosening up the motor restrictions a great deal, along with a number of other restrictions we faced in the past. Perhaps this trend will continue.

It is still not "use anything you want" and I would doubt if it will ever get there even given the battery/breaker/cost rules.

I believe it is still just a part of the effort to level the playing field for all teams.

One could argue against nearly any restriction in this way...but having some guidelines is not really that bad. We have limitations on pneumatics and the use of the control system... ... it is just part of the game and the challenge.

[Mr V]

As to interfacing the smaller motors with drive systems there are a number of pinion gears that are available that can be pressed on the shaft.

However since the introduction of the Versaplanetary and the addition of the motor specific mounting plates I can't see moving back to using any other way to interface with the small motors. If you don't want or need the reduction from the VP you can configure it in a direct drive manner. You then have a pair of hex and a pair of keyed round output shaft configurations to choose from. They also provide a nice solution to mounting since they can be mounted from two sides or the face. With proper planning for access swapping out the motor is a breeze, whether you need a more powerful motor or to replace one that has failed.

[Michael_Puckett]

Originally Posted by Bob Steele

...I believe it is still just a part of the effort to level the playing field for all teams.

One could argue against nearly any restriction in this way...but having some guidelines is not really that bad. We have limitations on pneumatics and the use of the control system... ... it is just part of the game and the challenge.

Yeah, I get that and think it's a reasonable thing to do, just seems like they could go about it in a way that's much less confusing for new teams to figure out. To limit motors by part numbers on one hand and application on the other sends mixed signals.

I had read about the auto salvage thing in the past and got the impression the rule might have just been pulled from the past as it was something they already had on file. I'd still like to see it re-written to better explain what exactly their intent was in bringing that rule back from the dead. If they're trying to limit motor size/power since the automotive applications they listed tend to have fairly similar motors, that's a perfectly good reason, but not really a good way to state it as there's probably still some crazy motor out there in that application if someone wanted to look hard enough.

It's like saying you can wear jeans as long as they are Levis, Wrangler, or Sonoma brand (part numbers), or any jeans that are blue (automotive application). So I can wear black Levis (becaues of brand), and blue Lucky brand (because of color), but not black Lucky brand, even though they're all essentially the same jeans. I can find the same motor with a different part number as a window motor, but it's not legal unless I can somehow prove it's the same motor.

I apologize for all the ranting, it's just been a frustrating week as our team is burning build time trying to understand the rules instead of building our robot. We've had to delay ordering the parts we're looking at because of this technicality, but every day we delay is another day behind we are on getting parts shipped.