Lithion-Ion Batteries
 

I've had this question in my head for the past couple of yearss, but still dont have a real answer. Why don't we use Lithion-Ion batteries for our FRC bots?

My team has used a Drill since 2006 that uses a Lthion-Ion battery, we love it because it doesn't stop working until the battery has appsolutely no more power in its battery.

I know that they're illegal, but why are they illegal? And won't it be better to run at 100% power all the time? You would always have the motors spinning at the same speed, there would be no more variables.

Thanks

Re: Lithion-Ion Batteries
 

I can speculate on a couple of reasons:
- Cost. Those batteries would be more expensive, and FIRST includes batteries in the KoP for every team.
- Safety. We've all heard stories about laptops or cell phones with Lithium-ion batteries catching fire or exploding, and that's the last thing we want in a robot! This is most often caused by abuse and physical stresses far less than our robots go through. It can happen during charging (while many people are next to it in the pits) or due to damage, such as being accidentally punctured by a robotic arm. While our current batteries can suffer some of the same issues, it's much more rare and generally speaking has a safer failure mode.

Re: Lithion-Ion Batteries
 

Besides cost and safety already mentioned, the engineering reason behind Li-Ion batteries not being suitable for FRC are the high current spikes we see.

All batteries are rated with a "C" rating that is a multiple of their rated current capacity. The "C" rating is what determines what is the highest amount of current that can be used to either charge or discharge the cell. For example, a 800 mAh 3.7v Li-Ion cell rated at max charge 1C and max discharge 2C can be charged at a rate no faster than 800 mA and discharged at no more than 1600 mA.

In general, Li-Ion batteries are never rated for high discharge capacities. Lithium Polymer batteries are better, and can have ratings in the double-digit C range, but these are not cheap. For FRC, a single Li-Po battery capable of meeting our needs would likely be at least $150.

Lithium Iron Phosphate chemistry shows potential, but is still too new and costly. LiFePO4 has lower capacities per kilogram than Li-Po, but is inherently a much safer technology. It will not explode or catch fire if mishandled or abused.

Re: Lithion-Ion Batteries
 

If one read the safety literature on LiPo batteries and then observed the types of practices put into use at competitions from the bottom 5% of least-safe teams, it would be easy to make a substantial argument against LiPo batteries for competition use. Simply put, it's very hard to trust all of our neighbors when a small mistake will be very costly (or painful).

Plus the GDC would have to amp up the requirements on battery placement/protection on the robot itself, and we all know the last thing we want are more design constraints.

Re: Lithion-Ion Batteries
 

We got a new Lithium battery powered cordless drill in 2008, and it worked ok for a couple years, then quit charging. Last week I figured I'd give it a try...and it showed that it was charging. Huh. Having a mysterious battery system that sometimes works, and sometimes doesn't work, is probably not the best thing for our robots.

Lead acid batteries (like we use) are pretty forgiving, very powerful, relatively inexpensive, etc. They're not high tech and not modern, but they are the best solution for the problem of powering our robots.

Re: Lithion-Ion Batteries
 

Speaking from the stand point of someone with a little bit of experience with LiPo and LiFePO4 batteries...

I agree with Art that LiFePO4 has a lot of potential, and a lot of cost. But there's another issue with those. Speaking from experience, to ship them anywhere, a) they have to go by ground and b) the originator has to have a particular certificate. They are lighter than an SLA, true, and provide pretty decent power, and can handle gentle to moderate motion forces... but I haven't seen anything more than that.

LiPo, properly handled (i.e., charged in a fire-resistant container and kept out of heat while charging, and kept from puncturing), is actually pretty safe. But, you do have to stop and take those precautions, which include monitoring the charger to take the battery off when it's done charging. And the odds of everyone actually doing so... Not good.


With regards to the second question, running at 100% power all the time: Could you do it, probably. But here's the problems:

• Battery Life--you think you go through batteries fast now...
• Variable speeds are useful, just ask your drivers.
• How are you going to get the power when you want it and not get it when you don't? Clutch design can be a bit tricky.

Re: Lithion-Ion Batteries
 

So with "Lithion-Ion" batteries the OP mentioned I thought I would try to clear some things up.
The three types of Lithion batteries that are commonish are:

Lithium-ion
Lithium-ion polymer
Lithium iron phosphate

The first two are often used mixed up, LiPo [Lithium-ion polymer] are an evolved version of Lit-ion [Lithium-ion], and LiFePO4 [Lithium iron phosphate] are an even more evolved version.

As stated above Lit-ion batteries would not be able to provide the amp draw that is required on an FRC robot, also they are pretty dangerous [remember exploding laptops anyone] and expensive. And they are out dated compared to the new LiPo/LiFePO4 in both safety, price and power capacity.

Now I run a set of LiPo packs to power my quadcopter, these are small ones at 2.2ap/hr rated for up to 40C draw current and they costed about 17$ each, and can be charged at 8C [in 7.5mins]. Personally I love them.

However for FRC usage, LiPo packs big enough [17ap/hr] would cost easily $150+ and chargers would cost like $120 each [ones that can change them fast...] as well as the PSU to power the chargers. Also most importantly LiPos are dangerous when treated incorrectly, I have heard of people burning down houses due to charging issues/mishandling. Also they are also not nearly as tough as the lead acid packs and require more thought on mounting and protection. LiPos do however have the highest power density of most commercial batteries which is why they are popular in the RC world but with the safety risks alone they are unsuitable for FRC usage [sorry but I don't trust rookies with high explosive batteries]. However a pack that big could easily provide the power to run an FRC robot while being lighter then the lead acid battery, but the life span would also be about the same [500 cycles] making them even more price ineffective.

I don't necessary agree with this, LiFEPO4 cells are price effective, very solid/safe, and rated for over 1000 cycles [Apple uses them]. But they are hard to get, not common place and have a lower power density compared to LiPo but still higher then Lead Acid. The cheapest method to get a A123 [well known brand of LiPoFE4] pack is to actually to take a part certain models of the Dewalt drill battery packs and savage the LiFePO4 cells from them and solder them up to make your own pack Click. However these are still expensive compared to lead acid, about $150 for 10ah/hr click and require an more complex charger to charge them [more $$$]. Price is the the main reason I see FRC not using LiPoFE4 for awhile.

I am not sure what this means, however even with LiPO/LiFePO4 batteries there is voltage drop when you draw large currents, and the voltages do flux as you use them. So you would still have to use PID/etc to account for different voltages when running things like a shooter wheel. And I doubt anyone in FRC would run there motors 100% all the time.

Also not all drill batteries are the same, some are great and last forever and some are crap and work for 5 secs [HF..] and not all Lit-ion cells are the same.

Re: Lithion-Ion Batteries
 

i've seen LiFePO4 (A123 type cells) batteries sold as SLA replacements sold by chinese companies and comparable SLA batteries are more than 5x less.

you can also buy PCM boards that make LiFePO4 batteries act like SLA batteries

Re: Lithion-Ion Batteries
 

Hijacking your thread: If FIRST were to take any technology from the RC world, I'd kill to be allowed to use brushless motors and ESCs in our robots. We could keep the expensive Jags and Victors to drive the CIMs for driving, if we had to. But, we would get tons better performance at a fraction of the cost if we could use brushless motors and ESCs. There is a good reason why nearly the entire RC world has made the transition to brushless.

Re: Lithion-Ion Batteries
 

This is the first time I've seen brushless motors suggested as a cost saving measure. Do you have a rough BOM of what you'd put in the kit spec'd out with pricing?

-John

Re: Lithion-Ion Batteries
 

Yeah... The same project that I worked on that used LiFePO4 batteries (a pair of 12V ones) debated brushed versus brushless, and quickly decided that the brushless ones were budget-busters (and we'd have to take even more anti-dust precautions than we did with brushed, which was a factor in that project).

Re: Lithion-Ion Batteries
 

Keep in mind that the RC world deals with vehicles that are a few pounds or less, thus the motors do not draw as much current overall. This alone leads to a less expensive motor controller.

Re: Lithion-Ion Batteries
 

They also go a heck of a lot faster, and energy required goes with velocity squared.

Just compare this Hobbyking brushless ESC to the IFI Victor. I am not a ground vehicle guy, so I'm not sure how the throttle linearity matches up to the Victor. Hobbyking tends to sell pretty quality stuff these days, and the independent reviews look great, so I would be inclined to say that the HK ESC delivers.

Re: Lithion-Ion Batteries
 

yup, it sure looks like the IFI spec sheet has more realistic current numbers.

Re: Lithion-Ion Batteries
 

you have to derate chinese esc's by like 40% to get a good idea of what kind of amps they will actually flow before they blow.

victors are overpriced anyways

http://holmeshobbies.com/product.php...t=0&featured=Y
http://www.botbitz.com/index.php?rou...&product_id=59

Re: Lithion-Ion Batteries
 

I'll take our shooter from last year as an example. We used a pair of RS-550 motors ($7.25 ea) driven by a pair of Jaguar drives ($119 ea), for a total of $252.50 system price.

That motor is 36mm in diameter, has a Kv of 1608 rpm/V, max current draw of 85A and max power of 254 Watts.

For an apples to apples comparison, Hobby King has a 36mm diameter brushless inrunner (S3674-1660) for $39.20 each. This motor has a Kv of 1660 rpm/V, a max current draw of 60A, and max power of 1600 Watts.

To drive it, we would need a 60A ESC. The HobbyKing Red Brick 60A ESC is $13.20 each. This ESC is a fraction of the size and weight of a jaguar, though it is controllable via PWM only.

So, using the motors and power drivers mandated by last years rules, we had a total of 508 Watts of power available at our shooter wheel for $252.50 total cost. If we were allowed to use brushless motor technology, we could have had 3200 Watts of power at our wheel for $104.80 total.

More power, less weight, less than half the cost. Note that the real driver of the cost difference is the drastically lower cost of the drive electronics. They can get that cost so low by removing all the smarts from the controller and making a bazillion of them. I wouldn't want to eliminate Jags and CIMS altogether, just allow these better technologies as an option for use where appropriate.

Re: Lithion-Ion Batteries
 

Lets take a look at that S3674-1660 motor a bit more...

power = current x voltage. Running at 12V and 60A, the maximum power input into the motor is 720W. Where's the other 880W coming from? It's a perpetual motion machine!

Realistically, that 1600W comes from running it at higher current/voltages. That motor is supposedly rated to 22.2V, according to the website. But even at that voltage, 60A only provides 1332W of input power!

So, all of these numbers need to be taken with a huge grain of salt. Without actually testing the motor with our system (in other words, take your proposed set up and hook it up to an FRC robot) and measuring the output, the comparison can't really be Apples to Apples.

Your numbers significantly overestimate the power this motor/controller combination would provide you.

Re: Lithion-Ion Batteries
 

Your comparison is completely unfair.

You are comparing US made versus Chinese made, you are also comparing an esc optimally sized for operation versus one far oversized for operation.

I love RC cars, and spend way too much money on hobbyking and can say with certainty I have used more motors and ESCs from them than anyone on chief. I love them for personal use, and a lot have surprised me with their performance and durability, but I would not put them on an FRC robot.

Re: Lithion-Ion Batteries
 

Very true, and good catch. I just took their numbers without checking their math first. My bad.

Let's take a look another similar motor listed: XK3674-1650KV Brushless Inrunner.

Specs.
# of poles: 2
Max Amps: 66A
Max Volt: 14.8V
Max Watts: 975W
Rpm/V: 1650kv

Running the math, the quoted max power actually equals the max current x max voltage. Derating to the 12 V on a FIRST robot (nominally) gives 792 Watts.

This one costs $31.86, so we get 1,584 Watts of power for $90.12 total.

Re: Lithion-Ion Batteries
 

I couldn't even begin to price that kind of thing, but it occurred to me I couldn't really price out the motors currently in the kit either. I know many moons ago nearly everything in the kit, motors included, were donated.

These days the number of kits has obviously grown and motor selection is a little more elaborate. Does anyone know how much of the in-kit motors are donated, purchased or ___? What about motors made available for purchase by teams? Are those discounted somehow?

Now that I think about it, I miss some of the old motors. The Globe motor was awesome.

Re: Lithion-Ion Batteries
 

Also reduce it to the maximum currents allowed on an FRC robot (it has to sit behind a 20, 30 or 40A breaker, remember!), and you're down to 480W.

I find it impossible to believe that this motor operates at 100% efficiency. There's no power loss at all due to friction in the bearings, or in generated heat in the motor?

The motors we deal with in FRC have been tested to death by teams, and the posted numbers are typically peer reviewed and confirmed to represent the output power available from the motor. The math we've done here can easily be applied to any of our motors to find the input power available to the motor, with identical results.

The key here is to look at the efficiency of the motor - that's where you'll be able to see actual gains in output power to your mechanisms. A supplier like BaneBots provides their motor efficiency right on the website. I ran a quick search, and I can't find any posted efficiency numbers for either of the motors you mentioned.

Granted, brushless motors are typically more efficient than brushed, but unless we know exactly how much more efficient, we can't really do a comparison. Is going from 70% efficiency to 80% efficiency (for example) worth ditching our current suppliers and sponsors? Is it worth ditching the known performance and longevity of our motors for new motors we have no experience with? Remember the debacle with the RS-775 case short a couple of years ago? I wouldn't want to see us make a drastic switch in our motors only to encounter something like that again... or worse!

Re: Lithion-Ion Batteries
 

Keep in mind you can't run at max power, nor even close.

These are non-sensored brushless motors, they aren't meant for torque or control loops, they will stutter (known as cogging) and fail to start.

They might work for conveyors, some might work for flywheels if they are way overpowered, but in most applications these low cost non-sensored brushless motors are not suitable for FRC.

Re: Lithion-Ion Batteries
 

I get what you're saying, but we can't be afraid to try new things just because they are new and untested in a FRC robot.

We have all been bitten by that bug in the past but we can't be afraid to move on. Who can't forget the debacle of the BaneBot gearboxes in 2007? Those were fun times.

Re: Lithion-Ion Batteries
 

I find the cost concern here difficult to reconcile. Every year there are many teams with a double digit number of batteries housed in large rolling cabinets. They have them labeled as practice, competition, good, ok, bad etc.

It seems to me that teams have a large volume of batteries to counteract a few apparent problems:
1) the batteries maintain inconsistent charge levels
2) these batteries degrade quickly over time needing consistent replacement and
3) the batteries cannot cope with a large C ratings while charging or discharging which causes the electrode/cathode degradation and results in 1) and 2).

Personally, I would rather have 1 or 2 batteries that work reliably even if they cost more rather than 5-10 batteries I have to babysit. At the very minimum it would be nice to have an option, any option, because right now there is no alternative.

Re: Lithion-Ion Batteries
 

792 is the electrical power input to the motor, not the mechanical power output.

For reference, the brushed motors used in FRC all have less than 50% efficiency at max power. Brushless motors share many of the same losses that brushed motors have, like windage, bearing friction, eddy currents, winding resistance, etc etc. I doubt that brushless motors are anywhere near 100%.

Sensorless brushless motors cannot operate at high torque at low speeds because of commutation issues.

Re: Lithion-Ion Batteries
 

I have no problem trying new things, I didn't mean for my posts to come off that way. I'm really trying to say here that we just need more information and testing done before these motors should be seriously considered for use by all teams. We'd need to understand their properties and be able to compare their specs directly to the "tried and true" motors we're familiar with, something no one has been able to provide yet.

I'd love to see a team adopt a couple of these motors and run them through their paces through a couple of off-season competitions. Find out how well they hold up, figure out how efficient the motors are. We're supposed to be engineers here... do we field prototypes as production equipment? Should we include a new motor we know little about and have no experience with in a Kit of Parts for thousands of teams, when we aren't even sure what the benefit (or drawback) of such a motor is?

I'm not saying we shouldn't look at these... I'm saying we need to make sure we understand the true benefits and costs before we start arguing for adopting them.

Re: Lithion-Ion Batteries
 

I'm a fairly new mentor, so some of my thoughts may not be as seasoned as the veteran folks out there. I'm seeing some assumptions in some of the responses that I don't understand.

There seems to be an assumption that for something to be legal for use on a FIRST robot, 1) its performance needs to be completely characterized, 2) it needs to be supplied to all teams in the kit of parts, and 3) it replaces whatever components were previously legal.

Where I can see how this MIGHT apply to control system components running software, I don't see why it should apply to things like actuators. I don't see a downside in allowing brushless motors and drivers to be included in the list of options we consider. Maybe they aren't right for certain applications, but for others, they might be. Why not allow teams who want to use them to save money to do so?

AdamHeard rightly pointed out that the Jaguars (and Victors) are far oversized for the shooter wheels. So why do the rules limit us to using those and only those motor drivers? Why not allow teams to use other options?

Reading between the lines, it seems that at some point in the past, cheap motor drivers were not available, so in order to ensure a supply of reasonably priced drives, FIRST worked with suppliers to come up with custom motor controllers. To ensure that the market was large enough to keep prices down, they made rules that limited teams from using anything else. I would argue that the commercial marketplace for inexpensive motors, drives, and controllers has caught up and bypassed the needs of FIRST. Inexpensive, rugged motors and drives, both brushed and brushless, are commonly available in the RC marketplace. For the $285 cost of the cRIO FRC II Controller, you can buy EIGHT Raspberry Pi computers (I have an order of three arriving today.)

During build season, I'm all about doing the best you can with the limited set of components allowed. But, with cheaper, possibly better, components available in the commercial marketplace, why not expand the rules to allow us to use them?

Again, I apologize for hijacking the OP's thread. If anyone knows how to split this topic off into a new thread, please do so...

Re: Lithion-Ion Batteries
 

Todd, I think I can address some of those. We'll let the third assumption slide as that's not necessarily true--the ARA donation and the BaneBots motors are good examples.

The second assumption is VITAL. If you're going to make a new technology legal, ALL TEAMS must be able to obtain it, preferably with minimal research. The easiest way to do that--and cheapest--is for FIRST to buy about 2000 sets of the item and distribute it via the KOP. Otherwise, you get the vouchers which may or may not be of any practical use. If it isn't in the KOP, it should be available from AndyMark/IFI/BaneBots/local retailers.

As far as the first assumption, YES! You do have to have characterizations! (We'll assume fairly complete, but not completely complete.) Why, you ask? How else are you going to size motors properly for the applications? Not all teams have the equipment to test the motors, or the budget to replace ones that fry during testing. Not having even an incomplete characterization can result in teams frying motors left and right--and even with an incomplete one... See Tetrix motors on minibots in 2011.


The paragraph on the reason for the rules, however, missed even the hay bales behind the target. That's not the reasoning at all. The original reason for the restrictions on the control system were so that FIRST technical staff (who are still comparatively few in number) didn't have to troubleshoot 40 different systems at a single event--and that is still a huge reason. Once IFI came along, it made life easier, as it was fairly easy to get teams a new control system every year--and teams with experience still managed to make dumb mistakes every year. The cRIO system was more powerful--and had a lot more issues the first couple years. See "limited technical staff not having to troubleshoot 40 different systems at each event"--and read the Einstein report again for how some teams, who've been using the system for years, made mistakes.

Having the control system the same is important, not because cheaper systems aren't powerful enough or tough enough, but because if you open the rules to more than one system, you introduce nightmares. FIRST recently put out documents indicating that they are looking for a new system--look at those, and see if you can come up with anything within their guidelines.


The motor system is the same way, except that it's limiting the maximum available power from motors instead of making the technical group's life easier. Same available motor pool = same available maximum power = no advantage unless you can put more motors from the pool on the robot and control them. It's been opening up a bit lately, but I think the main reason for brushless motors not being allowed is that the legal speed controllers can't handle them. But when you open up the pool of legal speed controllers, you have to make adjustments to the control system, somehow, or force the controllers to work with the system.

That's why, until the new control system comes out, I don't see brushless motors being legal, unless it's on a very limited basis (as in, the 2 motors must be Brand X, Motor Y, and each running on one ESC with BEC Model Z).

I'm not opposed to brushless, under the following conditions (legality is assumed):
--They have to work with the existing control system.
--There has to be a specific type or limited pool to draw from. (This would be opened up as teams gained more experience.)
--They have to come in either in the KOP or with an easy-to-use system to obtain them for a steep discount. Teams don't necessarily have the budget to go all-in quickly.

Re: Lithion-Ion Batteries
 

The current system has four types of regulated outputs:
-Servo PWM
-two digital lines (relays)
-CAN
-moderate current high-side drivers (solenoids/lights)

Almost any motor controller that exists in the hobby world will accept Servo PWM. The current code even allows tuning the pwm max pulse width - A Victor is narrower than a Jaguar, which is narrower than a servo.

There's nothing the control system really cares about, as long as a removal of the PWM signal guarantees the motor shuts off.

Also, as teams are regulated by the PD board (limited 40a breaker spots, and 40a max breaker size), the 120a main breaker, and the 50a battery connector, teams are already power limited electrically, without limiting motors.

As long as a motor is a COTS part that can be bought by anyone, I see no reason to make it illegal. You are limited by the main breaker and PD board, which effectively limit the power of individual motors and all motors on the robot as a whole.

Re: Lithion-Ion Batteries
 

Can you expound on this Adam? I don't know much of anything about their ground vehicle stuff, but I have spent in the 4 digit range on HorizonHobby (USA) and Hobbyking (Chinese) products. For starters, I think it's pretty unfair to say US made vs. Chinese made, as to my knowledge essentially all of their airplane products are manufactured in Asia. Are cars different?

Multiple times I have received defective components from Horizon, but I have yet to receive a defective product from HK. In my experience there is something like a 20% derate from advertised Chinese specs, but I've never had so much as a servo fail without reason. (And these are servos that you can buy for $4, so they cost significantly less to make) I realize I have a small sample size, but the fact that I've had 3 Horizon orders where components have failed within an hour of first flight just doesn't sit well with me.

Re: Lithion-Ion Batteries
 

In order for there to be more options, FIRST needs to understand and support the characteristics of those options. Otherwise, you could run into some dangerous situations. Some examples:
- What if a team figures their mechanism only needs a couple of amps, so they use a cheap 5A speed controller? Who puts out the fire when something goes wrong and it draws 20A during a match?
- How do you handle the situation where a team picks a motor that has a grounded chassis? having any sort of short to the frame can cause some major issues, both for your robot and for safety on the field interacting with other robots.

Further, how do you ensure sufficient quantity for all the teams that want a particular part? It's great to say that teams can use any motor, but what happens when the veteran teams buy up the limited stock of the most powerful motors, leaving the rookie teams to suffer? Companies like Banebots, IFI, Vex, and AndyMark are very invested in the FRC program, they know the typical demand every year, and can help to ensure that all teams have access (even if there are occasionally shipping delays for a week or two) to the parts we need. If we go with "common" parts from suppliers that aren't invested in the program, you run the risk we've encountered with game pieces (like Orbit Balls!) in the past - the company stops producing them, causing problems for teams during the build season!

Also, please remember that one of FIRST's primary characteristics is Coopertition. How can teams help each other if their systems are all different? How can you borrow a speed controller from someone if they use something completely different, with a different footprint and different characteristics? How can FIRST possibly manage a FMS (field management system) that ensures equality and safety for everyone if everyone uses a different robot controller?


Some advanced individuals or teams may certainly have the knowledge, experience, and ability to test, develop, and utilize alternative controls. Most rookies don't. Even some older teams don't. FIRST does its best to provide a consistent platform for every team, so everyone competes on an equal footing.

Re: Lithion-Ion Batteries
 

Eric and Jon,
Thanks for the educational replys. You are speaking from a background in FIRST I just don't have yet. I appreciate the discussion.

I agree that it should be commercially available, but don't see how it's necessary that it be in the KOP or available from those particular vendors. There are plenty of things that are legal that don't fall into those categories. Colson wheels, for example, or any gearbox you can dig up or cannibalize from a commercial product. And why should our collective entry fees go for parts we don't want or need? FIRST has recognized this issue and said that next year, teams may elect not to even get a standard KOP, electing to accept a voucher instead.

It seems to me that FIRST has already departed from this premise. See last year's [R48], part I: "up to 2 window lift, seat, windshield wiper or door motors obtained through either the FIRST-Automotive Recyclers Association partnership or from a prior years’ KOP." Since we were already allowed to use junkyard motors, with no info on their performance characteristics, why not brushless, too?

I think Palardy was right when he said pointed out that as long as PWD is used for signaling, the control system doesn't care if the motor driver is brushed or brushless. He also pointed out that using more powerful motors gives no advantage when all teams are electrically limited by the fuses on the power distribution board to a maximum of 480 Watts per motor (40 amps x 12 volts).

This is a very good point. I wasn't able to think of a likely safety problem, and this is one. But, it could be simply solved with a rule specifying that any motor controller be required to handle a minimum of 40 continuous amps. Any more is unnecessary, because the fuse protection mentioned above.

You both brought up the issue of suppliers being able to carry adequate stocks of parts to supply all teams who might want an item. I'm glad you did. This is an issue that bothers me a lot, and has caused our team to redesign mechanisms when vendors run out of stock on popular items. The rules are very specific about how a vendor must perform in order to be "a legitimate business source for COTS items".

Specifically, last year's [23]:
C. "The Vendor must be able to ship any general (i.e., non-FIRST unique) product within five business days of receiving a valid purchase request. It is recognized that certain unusual circumstances (such as 1,000 FIRST teams all ordering the same part at once from the same Vendor) may cause atypical delays in shipping due to backorders for even the largest Vendors. Such delays due to higher-than-normal order rates are excused."
D. "The Vendor should maintain sufficient stock or production capability to fill teams’ orders within a reasonable period during the build season (less than 1 week)."

Notice that a small shipping delay is acceptable, but running out of stock is not. From my reading of Chief Delphi and the experience of our team, neither BaneBots nor AndyMark would remain legitimate COTS sources if these criteria were strictly applied. Does FIRST maintain a list of qualified vendors? Has anyone ever been removed from this list for non-compliance? Since FIRST seems to allow vendors to slide by with a "well, they tried their best" attitude, why should this standard be strictly applied to any other vendor? Our team has learned from experience to buy critical parts during the off season, so that when the build season starts, and AM and BB run out of their stock, we don't end up on the short end of the stick.

The low cost of brushless controllers and motors, and the wide range of available options (these days they are practically a commodity) makes the at-risk investment in a couple of sizes of motors pretty low. Pre-buying a half dozen $20 ESCs beats the heck out of stocking up on $120 Jaguars, like we do now.

I think you are both right about the dangers of fragmenting the control system. That would just be a terrible idea all around. But, when the time comes to reevaluate the standard hardware, I hope a more open, less expensive system like a Raspberry Pi/Arduino controller gets a fair shake. The drawback to something like that is it might come with very little vendor support. Having the NI support staff available to work out problems is a big plus for a big name vendor.

Re: Lithion-Ion Batteries
 

The time has already come - we'll have a new control system in 2 years. This should help give you an idea of how detailed oriented FIRST is being in determining the right system for us to use when they go about changing it!

http://www.chiefdelphi.com/forums/sh...d.php?t=108083

Re: Lithion-Ion Batteries
 

I'd be interested in hearing this too, Adam.

My wild guess is that RC cars have very little load, and the RC car parts just won't be able to handle the mechanical loads we subject our robot motors to.

How did we get here from Lithium batteries? huh

Re: Lithion-Ion Batteries
 

I don't think it's been mentioned yet, but the derating for Lead-Acid batteries is a big factor. They're rated for 17Ah at 1 Amp but in FIRST use, drawing triple digit amps, their capacity is going to be closer to 6 or 7 Ah.

Re: Lithion-Ion Batteries
 

OK,
I think it is time to enter a few real world numbers to the discussion both on motors and batteries since a lot of data has been quoted from various sources.

As to the motor controllers now in use, while rated at 40 amps, these devices regularly survive 130 amp peaks when driving CIM motors at or near stall. The Victors are a little better at this than the Jags due to the intelligent monitoring in the Jag for faults. The Jag monitor tries to limit over current by faulting.
While everyone likes to look at the limits of the electrical system via breaker size, all FRC breakers withstand 600% overload for a short periods of time (seconds) without trip and easily handle 200% for several seconds.
First has always attempted to keep some simulated real world limits in the rules to force creative thinking using a defined set of parts. It is for this reason that many "legal parts" choices are made. If a team were to gain an advantage over other teams by simply finding an esoteric part, that while stocked was not generally known or available, that team would have gained a real advantage over other competitors. While this can be viewed as "holding back" some teams, it allows everyone to compete using the same components for producing mechanical power on the robot.
As to the battery choice, the AGM SLA batteries now in use are 1/4 the price of other battery technologies while providing more than twice the peak output current at a fraction of the series resistance of these other technologies. One item that many teams ignore or forget is that our batteries have a defined life (charge/discharge) of 400 cycles. This life is shortened by severe use resulting from high current demands. Robots designed with inefficient mechanical systems will regularly exhaust a battery in one match. While I have no real data, it would seem that these teams shorten that 400 cycle life by 1/3-1/2. While the lithium technologies have some interesting specifications, please look at the series resistance or impedance. Then calculate the internal voltage drop for say a 400 amp spike and the 12 volt battery Li suddenly is making 0 volts at full charge instead of the 8 volts that will be available from the SLA battery now in use.
As to the use of brushless motors, it would be nice to make some types legal in the future, I agree. However they have serious limitations in general use as several people have already discussed. The teams need to be informed on their best use and implementation.

Re: Lithion-Ion Batteries
 

I don't remember exactly on the PWM front, but I remember hearing something about the Jaguars/Victors using a slightly different PWM than say a servo/ESC. I think it's PWM vs PMM, but can't for the life of me remember exactly which is which.

Palardy, there's a minor difference between the max power being regulated electrically and in the motors. The electrical max power is driven by the current limits (and subject to the breakers actually tripping when they're supposed to, and as we all know they can handle short overcurrents)--the motor max available power is driven by the motor characteristics. If I can use 20 BaneBots without tripping a breaker, and you can only use 4 CIMs and 2 FPs, but you need 5 BaneBots on top of that that you can't use without the breaker tripping, I have a higher max available power and somehow worked in a way to use more of the electrical max power. Unless, of course, I used very weak BB motors...

A couple of notes on speed controllers: I would like to see some USB-capable ones available, and I recall that FIRST is looking to add those. However, I would actually raise the minimum from 40 to 60 (and if you meant maximum, so did I). Some of those controllers have ridiculously low safety shutoff settings, which don't account for the startup current that a motor can draw. (That current is why a breaker is used on the compressor spike instead of a fuse.) Trust me, I've seen a controller that was rated for at least the current my team was putting through it shut itself off 5 seconds into a 10-minute run--and the fuse protecting the circuit, rated for the same or less than the controller, didn't blow or show signs of blowing. A lower-rated controller, with the safeties shut off, went about 7 minutes in the same position before releasing smoke--it could have gone longer but wound up with an unusual load when the terrain shifted. And that controller was rated well below the expected current...

Oh, right: How it's necessary that a part be in the KOP. Teams were supposed to go buy a Kinect last year? That was also a new and readily-available technology. ;) In all seriousness, it's not, but I'm willing to bet that the economics of scale are better for 2000 than for 20. Motor technology is one of those things where it's better to introduce it in the KOP--then teams will have a better collective knowledge on how to handle it, and where to buy it.

I wouldn't quite say that the ARA allowance last year was quite without performance characteristics. For one thing, van door and seat motors have been in the KOP before, and the van door motors were available from AM (which does provide the spec sheets); for another, if you need to look up the characteristics and you have a motor part number, that's pretty trivial with an internet connection.


I'm thinking that squirrel is right on not putting R/C components on FIRST robots due to the loadings. If you're stalling a R/C motor, you're doing something very wrong. At least, that's the aviation side of the theory--I don't know about the ground vehicle side. How often do FRC motors stall or come close, especially in a pushing match or a robot autonomously running into the wall?

Re: Lithion-Ion Batteries
 

Well, depending on your point of view, I very rudely pirated Aaron's thread, or I nudged it to include discussion about a wider variety of technologies not currently allowed by today's set of rules. :)

Re: Lithion-Ion Batteries
 

1/10 of a second max for the 40 amp breaker @ 600% overload (700% of rated load) according to the snapaction spec sheet for the MX5:

http://www.snapaction.net/pdf/MX5%20Spec%20Sheet.pdf

... am I looking at the wrong doc?

Re: Lithion-Ion Batteries
 

I wanted to expand on these two paragraphs, real quick.

First, on ARA motors. I inspected at two regionals, and didn't see a single ARA motor. Even though it gives teams a wide variety of choice, is readily accessible, and was completely legal, a vast majority of teams decided to stick with what they knew. Using a motor in the KoP has two advantages: you know it's characteristics, and you can test it since you have one sitting right in front of you. With the ARA, you go to the junkyard, get a motor, then have to take it back and see if it'll do what you want. Those extra steps and unknowns make it not worthwhile for most teams during a time-constrained build season. It'll be interesting to see how many teams used their voucher to get motors in the off season, tested them and understood them, then decide to use them this upcoming year.

Next, on stalling. I don't think there's a single motor my team has ever used that hasn't been stalled. CIMs stall all the time in pushing matches. We've stalled (and burned out) FP and BaneBots motors. We destroyed quite a few Tetrix motors. We stalled the window motors during prototyping on our BreakAway robot, before we figured out our final design. We briefly stalled the AndyMark gear motor this last year almost every time we used it. With RC cars, you're more likely to suffer wheel slip than stalling - the cars are so light and the motors spin so fast, even driving it straight into a wall will just result in the wheels spinning while you go nowhere.

Finally, one more thing to consider: The more options you add, the harder inspection gets for everyone. If you add a speed controller that can only be used with 20A breakers, then inspectors need to check that. If you open it up completely and allow any speed controller that meets certain requirements for current, voltage, thermal shutdown, etc, then the team would need to bring documentation for that speed controller, and the inspector would need to be able to understand that documentation. This is something teams are notoriously bad at doing (I've encountered a lot of situations where a team uses a pneumatic part that we need to verify the operating characteristics of, and they don't have a spec sheet with them. With no internet at the venues, getting one can be difficult!). The last thing we need to do is introduce additional inspection headaches!

Re: Lithion-Ion Batteries
 

Getting back to Batteries, there are really good LiION technologies available that would be ideal for the FRC bots. I've been working with Enerdel the last couple years on various projects, we put some of their 17aHr LiION cells in our Combat Heavyweight (220lbs) which easily spikes 400amps at 24v and had no problems, it would run for ~hr when not in a fighting match during testing. LiION don't have the same safety concerns as LiPO, like any stored technologies, they can still be dangerous, but won't spontaneous combust like LiPO, we’ve accidently poked holes and shorted a couple of the cells and never had a fire like LiPO are prone to do and hence have caused airplane restrictions. As mentioned, Li batteries are typically rated by a “C” factor which is discharge amperage proportional to capacity, and the discharge capacity of Li technology is also related to the actual surface area of the Li anodes. So unlike the “hobby” batteries made for short high discharge burst, Li technology made for the automotive, military and commercial applications are large flat packs to have maximum anode area for sustained higher amperage discharge without cell damage, say a equivalent to the SLAs used currently in FIRST FRC in an automotive type LiON would be a ~6X7X1” flat pack and would weigh ~2lbs in packaging.

But as many of the senior mentors have noted in this thread, the issue is cost and logistics. The technologies that are key to making the competition "fair" for all teams are the batteries, motors and controls that everyone is allowed to use. Simply supplying some of these newer technologies to more than 2500 FRC teams is HUGE for a non-profit trying to do things “inexpensively”. If FIRST was a big company doing billions in business, the challenge wouldn’t be as great, but regardless of some gripping about cost, FIRST does a lot with the budgets that they have to work with and switching to a different battery tech right now is cost prohibitive, IMHO.

FIRST FRC isn't necessarily a "use the most cutting edge" technology challenge like some technology competitions, but more like a “here’s what you have to work with, make it happen” situation. Believe it or not, this is more real world realistic. Some deal better than others, but all have the same opportunity.

Re: Lithion-Ion Batteries
 

Ether,
You are looking at the correct document. The graphed trip times are the guaranteed "must hold" times. Typical is a little longer. As a reminder, as the temperature goes up, the trip times will go down.

Re: Lithion-Ion Batteries
 

You can just call it a Servo in code and be done.
The only thing that is different is the width of the PWM pulse. Servos use a pulse between 0.5 and 2.5ms, Victors use 1ms to 2ms, both have neutral or center at 1.5ms.
In LabVIEW (I assume C/Java are similar), the Motor cluster type includes a definition of each of the pulse positions for scaling, adding additional motor controllers that fit between a Victor and Servo are quite easy.

In any case, the mechanical power available is a factor of electrical power and motor efficiency. Any brushed motor significantly larger than a CIM used in a FRC drivetrain will likely trip the breaker - There are many teams who underpower their drivetrains and already trip the 40a breakers.

In addition, the 120a main breaker and battery limit the total available power of the machine. Drawing too much instantaneous current will lower the battery voltage due to battery resistance, and too much sustained current will trip the 120a main breaker. It's also possible to melt the 50a battery connector. I have personally driven a robot to do both in a competition match (although the battery connector was in the off-season).

Also, every motor, speed controller, gearing, and wire is weight. Weight (and often time) is the most precious thing on a FIRST robot.


I don't think it's a requirement to put the part in the KOP if it's commonly available. If FIRST were to allow certain types of motors (e.g. all 5xx-sized brushed motors), there would be many places to get them from (e.g. many cordless tools use 550/540 sized motors, you can get them at home depot if you want). The only exception is the control system - Since the FRC control system must be used as is, the base control system should be included (ideally every year).

Re: Lithion-Ion Batteries
 

Which is why I asked about the Kinect. You can go into any store that sells video games and buy one if you think it'll be useful. So why bother putting it into the KOP, like FIRST did last year? You could just give every team a voucher good at the local Best Buy or similar store that says "Good for one free Kinect".

And, just to beg the question: If base control system components should be included every year, why isn't the cRIO in every kit the last couple of years?

The way I look at this sort of thing is: If there's a change to the control system, especially a major one, it needs to be in the KOP. If there's a change to the motors, start with one or two in the KOP--it helps to have something in your hands that you can monkey around with. If there's a change to the hardware, make it available in the KOP/FIRST Choice--but teams will change that anyway.

tl;dr: If an electrical or controls change needs to be made, as it would with a new battery chemistry or brushless motors, put it in the KOP for one year. After that, it goes in rookie KOPs only; everyone else gets to use vouchers or local sources.

Re: Lithion-Ion Batteries
 

I would only change that to read "put it in the KOP for at least one year" :)

There are some cases where it makes sense to keep things in the KOP year after year. For example, the robot chassis, with the included CIM motors, gear boxes, chains, wheels, and sprockets. I love how FIRST addressed removing it from the kit for those who opt-in, though... it makes sure that every team can get something driving.

I have mixed feelings about the control system, though. While I want everything (including the cRio) included in the kit every year so we don't have to dismantle old robots, that gets to be extremely expensive and wasteful. How many 20 year old teams do we have that have shelves of robots at their build space doing nothing but gathering dust? I would rather dismantle some old robots to get control system components back than have to sacrifice anything else in the KOP just to get a new cRio each year.

Re: Lithion-Ion Batteries
 

Andrew,
While I have seen some teams trip the main breaker, the majority of those were due to significant vibration imparted to the breaker assembly or in a very few cases, a manufacturing defect within the breaker. This year, with the additional motors allowed, main breaker trips occurred more often than anytime in the past but those were still few and far between. While I have inspected many melting failures of the Anderson Power connector on the battery, all were due to damaged connector parts or improper crimp of the terminals used. By far and away, scratching of the surface of the terminals is the most destructive. This is caused by teams who use the alligator clips supplied with the battery charger to clamp on the Anderson terminals to charge the battery. The clips cause significant scratching and gouging of the terminal face which results in high resistance and skyrocketing temperatures. In some cases, teams deformed the springs that support the terminals to allow easier mating/unmating of the connector. This again results in high resistance and localized heating of the terminal. For instance, imagine a damaged or poorly mated terminal that has a series resistance of only 0.1 ohms. At a 200 amp load current, the terminal resistance is trying to dissipate 200^2 amps * 0.1 ohms=4000 watts. Yes, that is the same as 40 100 watt light bulbs in the space of 0.0625 sq. in. And as you can imagine, that is capable of melting plastic.

Re: Lithion-Ion Batteries
 

When I was young (and immortal and reckless) I tried to change the starter motor on my 68 Camaro without disconnecting the battery.

My metal watch band shorted out, and the surge of current melted the metal and popped the watch right off my wrist.

Re: Lithion-Ion Batteries
 

Al,
I can personally vouch for Apalard on this one that it appeasred to be an over-current issue.
Our robot this year had a very high top gear which tended to draw a lot of current. The first trip occurred at Troy, when our bot was beat to the bridge and had 10 seconds of stalled acceleration in high gear. Shortly after the start of the match, the breaker tripped when another stall condition occurred.
This condition was repeated again in anotehr series of matches at Troy. After that weekend, we pulled up the spec, tracked voltages, and figured out currents. The current, and time at current matched the likelihood of tripping the breaker.

We then bought a handful of breakers and tested them with a power-supply versus the loads we were seeing on that powertrain, and the tripping of the breaker matched.

We had also been warned by our friends across the state that ran a similar drivetrain in 2010, that the layout is "power hungry" and a "battery hog".

I wish we would have documented the testing process on the breaker better to do a little white-paper on "what not to do" when doing a wide bot.

The combination of a longer wheelbase (even though it was wide), higher traction profile, taller gearing along with Apalard's aggressive drive style tended to cause high drivetrain loads. The inefficiency of our collector also tended to have the collector motor (a 550 or 775 depending on event) running at/near peak power.
************************************************** ************************
The pit crew re-geared the drivetrain at MSC and then again at Champs, and the tripping of the main breaker issues went away. With the re-geared drivetrain, it pulled significantly lower current in the drivetrain. There were a lot of hard crashes, and hard bumps may have tripped the breaker, but I believe the high current draws played a big part in it due to the specific times I saw the breaker trip.

Re: Lithion-Ion Batteries
 

Ether,
You were very lucky. I may ask you to describe in detail this story when we discuss battery safety during the build season.
Ike, if you have the battery connector that melted, I would really like to see it. Also might you have a picture of the robot side of the battery cable and main breaker? On occasion, the temperature rise from damage at the connector has been transmitted through the #6 wire to the main breaker causing early trip.