Driver station power
 

I am designing an advanced driver station for our team, and I was wondering if a car battery would be allowed as a power source. I would use a shunt connected to the mcu to monitor the battery conditions and see if it would be safe. Are car batteries allowed at the competition if they are not on the robot? If anyone is interested in the project, the homepage is at: http://devstuff.no-ip.biz:890

Re: Driver station power
 

From previous Q&A:
http://forums.usfirst.org/showthread...-Extra-Battery

Re: Driver station power
 

I believe there are available power strips or individual sockets at each of the driver stations on all fields. I'm pretty sure they are available at all venues, if you need power.

Re: Driver station power
 

I was wanting the cart to be portable, and I wanted two BAG motors aboard to help reduce the weight of many batteries; otherwise, the 15 amp outlet would be the best solution

Re: Driver station power
 

I believe there are connectors for the KOP driver station computers, however teams not running that computer can not benefit from them.

We wound up connecting a 12v robot battery to a 120v inverter, and powered the laptop charger directly. This saved us on a number of occasions, going into matches only to find that the driver station battery was about to die as we were setting up.

Re: Driver station power
 

I am talking about a 2000 watt inverter connected to a car battery, breakered and fused. I am willing to place every safety feature possible, like current watch and temp watch. In my current schematic, I am having 250 amp MOSFETs powering everything so if too high of a current is detected, an automatic shutdown of that component for a set amount of time. It will also have a display and a usb-serial plug to the driver station and control EVERYTHING, even the power TO the motor drivers (victors)

EDIT: I am also thinking of placing the battery inside an ABS holder, because of it's resistance to acid spills. We would smell a spill before it becomes too late.

Re: Driver station power
 

Who is going to carry this monster?

Re: Driver station power
 

A robot battery and one of these should suffice.

Re: Driver station power
 

This is kind of overkill, but this is what I was looking at. However, the price tag isn't the prettiest. However, we could start out with a small inverter to just start off with and if we decide to do something like charging robot batteries on the fly, maybe upgrading to something similar to this would be feasible. However, the inverter that Gregor linked to was the first one that I looked at. BTW, has anyone visited the site that I posted and think something is impractical?

Re: Driver station power
 

Use solid state relays not MOSFETs.
Still not really sure why you have such high current requirements.

Also...

Propeller input + voltage divider = 5V tolerant input :)

Re: Driver station power
 

This response was for a time when power was not supplied in the driver's station and this became the FRC recommendation for that year.

We are very concerned about safety in all areas of the competition and moving a heavy, liquid acid battery and high voltage source pushes the envelope on that precept. Additionally, there is very little floor space in the driver's station to place your equipment. There is no substitute to having the laptop battery charged before you come to the field. And while nice, most teams find there is no substitute for charging batteries in the pit prior to coming to the field.

More likely to be invoked is this...
4.1.11.4
R93
The OPERATOR CONSOLE must not exceed 60 in. long by 12 in. deep (excluding any items that are held or worn bythe DRIVERS during the match). There is a 54 in. long by 2 in. wide strip of hook-and-loop tape (“loop” side) along the center of the PLAYER STATION support shelf that may be used to secure the OPERATOR CONSOLE to the shelf. See Section2.2.9 for details.

Re: Driver station power
 

In 2011 Team 11 was given an approval to use batteries in flashlights at the driver's station

However I agree this seems extreme and of course rules change. Those flashlights would not exceed the driver's station dimensions but we scraped it early on. It was for a camera tracking system we did not need.

Considering that a laptop charger is usually < 150W and < 30V.
I do not understand why anyone would need the sorts of current listed at the link.
If you must charge a laptop from a battery why not get a universal laptop car charger and put an Anderson Power connector on the end for a FIRST approved robot battery?
At least then you should have plenty of opportunities to charge that robot battery.
Plus handling the robot batteries is typical for this competition.
Plus a laptop charger meant to work in the car will not put out wall socket voltages.
So there's much less risk of some unusual accident.
Plus 150W max is no worse that 2 CIMs dragging on that battery.
Finally the custom electronics power supply on the robot would work at the driver's station (with less issues).

Course again it is entirely at FIRST's discretion if they allow this in future years.

I will also add that in past years while in various volunteer positions I've had the crazed experience of trying to help a team find a replacement laptop battery at a competition (laptop batteries are not cheap and the software just takes hours to install). Lucky for those that got one I have several friends with computer stores and piles of questionable laptops they can part for a used spare. Usually my friends have been good enough to just give them the battery which is generous considering it's a zero notice demand and sometimes they've even delivered it (hey that was not 30 minutes or less :)).

I myself have a universal car charger with an Anderson power connector and a few tails just in case something like this happens. I come prepared (I even lately bring a spare dual core laptop suitable as a driver's station with most of the software and updates installed) and the mess stops with me. However I would never offer this up as a solution without confirming with the field crew they understand what is going on (even if the rules might allow it in any given year).

Re: Driver station power
 

We have always plugged our laptop in the pits between matches. We have had close calls. Especially in the finals when you do not go back to the pits between matches. We are looking at putting power on our cart for this reason.

The FRC legal battery with a small inverter will keep your lap top charged. Since it is the same battery as the robot, you get a spare robot battery or you can use an older robot battery that doesn't have the umph for competition. A lot less likely to raise a flag with the safety people since there are 100s in the building already.

Re: Driver station power
 

you could also use a computer that has the same power requirements as the classmate.

Our Lenovo x61 laptop-tablet computer has a power adapter that uses the same connection just before the power brick.

Re: Driver station power
 

Please don't plan on unplugging parts of the field at your whim.
The field provides a barrel connector for a Classmate. It doesn't provide any other plugs.

Re: Driver station power
 

I am changing my design a bit. We want our laptop to be able to come off the cart, so I thought of designing a docking station. Are supercapacitors allowed in the driver station? They could probably hold power for use in a little time, and they would charge in no time! Also, I am thinking of dropping the idea of to car battery. Something safer might be better. Also, the team doesn't want the two CIMs because of safety issues. That means that a 6.6 volt LiFePO4 battery at 5000 mAH should suffice. I am expecting the control panel to draw a maximum of 500 mAH, monitoring all batteries, highest PLL and display on highest brightness. BTW, if anyone has been on my website, http://devstuff.no-ip.info, please tell me any concerns or ideas for my 'advanced driver station'. Also, does anyone know how to model a hinge in inventor? I want the drive station to have a little of stashing space!

Re: Driver station power
 

Regardless of legality in FRC:

Per the other topic where I mentioned supercapacitors please be sure to consider internal resistance when you consider this.

The better capacitors from DigiKey are much lower ESR.

Also along with that 'charging in no time' consider what your in-rush currents will actually be for whatever large capacitance you are considering.

I'm still not quite sure what you are powering with all this.
Netbooks and laptops generally have internal batteries.

Re: Driver station power
 

LiFePO4 at 5 AH? If you're only doing the monitoring, you can probably get away with that. (Barring safety, which I'll get to.) But if you're charging batteries, I'd use something with a lot more charge capacity, say the car battery or maybe a deep-cycle battery.

LiFePO4 batteries are known to need care. Shipping: You can drive 'em, but if you're going to ship 'em you need someone certified to do so at both ends; if you're going to fly 'em, you really mean you're going to drive 'em. No joke. They are a bit less flammable than LiPO... but that's not saying much. Gotta take care of 'em. Oh, and they're not cheap.

Concerns:
--Display panel is OK, but why does it need to integrate with the driver's station? Make it separate--use an ancient laptop or something similar. The DS doesn't need to know that stuff
--You're asking for trouble with the magnets, particularly. Do it just right, you're OK--MAYBE. Do it wrong and the least you can expect is a pinched finger or ten depending on how many are caught between the driver station and the cart. Maybe a bit of a shock, delivered to a person. Maybe some electromagnetic interference. You get the picture.
--No power switch to cut ALL power is listed; that's probably a good idea in case something goes down.

If I were you, I'd stick with a car battery, and use PowerPole connections for all power to the driver's station laptop charger--no magnets whatsoever--and have another means of lockdown. Or, seeing as you're thinking of having an outlet on the cart, just use that.

The REAL question is, Why are you NOT using your laptop's INTERNAL battery, and just charging that?

Re: Driver station power
 

Thank you for the feedback. I think I may have forgotten to put on my site that the current draw will be monitored. If the current draw ever goes too high in some part, an automatic shutdown of that part will happen. Also, the battery cart, as my team is saying, if typically going to be plugged in. About the display, the Propeller chip, what I am currently wanting to work with should be very easy to interface. I want the battery cart to think for itself...Monitoring battery charge levels, and selecting the perfect battery for the next match. (our team likes to switch out batteries almost every match). Also, we are using the laptop internal battery. However, incidents where it doesn't charge are often so this is to limit that. The small battery will be just to power the control panel. Also, I did chose LiFePO4 because we do not have very high space constraints currently. They are also a lot safer than LiPolys, especially because I probably will 3D print a perfectly fitting mount for the battery. Because of the want for simplicity, I would like everything to dock together, and the magnets won't be way too strong to hurt someone. We probably have more dangers around the power tools than we would have with these magnets. Just to make it clear to me, the team and anyone else wondering, The magnets will conduct, not induct. If that won't work, I will put metal sheets and brushes for the contacts.

Re: Driver station power
 

Theory is a nice place... I suggest having one point with a big, easy-to-hit button or switch to shut down the whole thing. If that current draw happens to be in the monitoring circuit... This is just for extra safety, mind you. Also to keep the safety folks happy. It's easier to put it in now, during design, than to add it later.

Bear in mind that if the cart comes out to the competition floor, power drops may or may not be available. Most regionals, probably not; Championships typically does have something.

I think there might be something funny with the laptop charging system. If that's the case, maybe putting a new charge system to get to the laptop isn't going to help. That, or you still have to remember to charge it (AKA plug it in/put the station on the cart).

True--but remember to take care of them. The 12V LiFePO4s I've had experience with would take up the exact same space as the 12V SLAs used on an FRC robot. Matter of fact, the LiFePO4 vs SLA debate hinged on weight and voltage drop pattern. (LiFePO4 won both categories, despite losing cost.) A perfectly-fitting mount does virtually nothing for battery safety, BTW--I've seen the effects of overcharging a LiPo when a good mount would have done nothing. I've seen SLAs spark while charging on a normal charger--I think there was something funny about the setup, but what escapes me. Can't say I've seen anything with LiFePO4s, but I've heard about the hazards. Note the transit comments earlier--LiPos, IIRC, have similar constraints unless they're in a special container, and maybe even then.

Again, just take care with the strength. I know I've had a project designed for rare-earth magnets where I had to make it clear that nobody but nobody was to put their hand between the magnet carrier and anything metal. Admittedly, 20+ magnets in a small steel disc can easily be way different than 4-5 spread out over an operator console--but will those 4-5 actually hold the console on the cart when it goes over a bump?

Just for safety's sake, please please make it darn near impossible for anything that ISN'T the driver's station to contact both magnets--or whatever the contacts are--at once. Maybe have a cap over one or more when the station is off--on both the station and the cart. (I'd say impossible... but then someone would find a way to connect both through him/herself. It's a law of nature.)

Re: Driver station power
 

Dev,
Your last post is kind of confusing. Can you describe exactly what your plan is? Your link above doesn't work for me so I was not able to review your design.

Re: Driver station power
 

Lenovo G and Z series (maybe more) have the same power adapter as the classmate so we just always plug into the field with the provided power.

Re: Driver station power
 

Why all the fuzz about spending lots of money buying batteries and inverters? Why not just buy a spare battery for the laptop? So you always have one charging in the pit. Better yet, in addition to a team laptop, one of our students has his private laptop installed with everything including Wind River, driver station, dashboard, and all updates. We have peer-to-peer source control. Whenever we make changes, we push the code to a USB flash drive, so it can be pulled by the other laptop. It actually saved us one time when the team laptop's network was malfunctioning. We just transferred the code to the other laptop and ran with it for the rest of the competition.

Re: Driver station power
 

Yes. Great idea. Why did I not think of that? A solid state relay could support a higher current throughput, getting less toastier. Also, I have already figured out the voltage level conversion for the chips. A backwards zener diode, rated at 3.3 volts will regulate the voltage, bringing it down to roughly 3.3 volts.

Re: Driver station power
 

?????

Re: Driver station power
 

After making the changes that I am working on, It seems that it won't be way too heavy. Maybe 100 pounds max without the batteries. There will also be castors for it to move on. During transportation, the driver station and the car battery will be removed. Also, no battery will be present at that time. The carry weight should then be pretty low.

Re: Driver station power
 

We used a deep cycle boat battery attached to an inverter last year. We also used it to charge frc batteries while moving. A deep cycle will last much longer than a car battery as they are built to be discharge fully and recharged unlike a car battery which is being topped up by an alternator.

It was approved but we were told that we had to make an enclosure for the battery to help prevent shorts and spills. We encased it in a vented MDF enclosure (not the safest thing but it did the job). We lugged it around in on our cart during queue and then it was carried by our driver to the station. It was super heavy but we only charged it once or twice a season.

This year we're using a 11.1v 60AH lithium battery I made myself from recycled makita packs which is muuuch lighter and 1/2 the size but about 1/2 the capacity and a bit more expensive. It can be brought on a plane if you tape the contacts and you seal it in a bag.

Re: Driver station power
 

Marcus et al,
I have to say that I am concerned about having inverters on carts where no safety ground exists. A simple inverter for a laptop power supply on the surface should not be a problem if all devices are functioning normally and are fully insulated. However, with the lack of safety ground, the potential for contact with exposed metal parts on the robot cart does exist. I must warn everyone that 110 volt wiring can be lethal and should only be considered when under certified electrical supervision.

Re: Driver station power
 

While it is a risk we have some precautions in place in case of that. Are entire cart a driver station board is wood and the inverter is fused in case of a short. One of our mentors is also EE and a certified electrician.

Re: Driver station power
 

Wood can make a suitable conductor. Even paint can contain additives that conduct. Fusing only protects the wiring.

Re: Driver station power
 

Do you have the same concerns about automotive voltage laptop chargers and a battery charger based on a DC/DC converter topology? In that setup there is no 110VAC.

I am not making light of this concern. Even a car battery can give you a nasty burn. In fact in my experience -48VDC DC power sources tend to make some of the worst burns if they can find a path of conduction.

Re: Driver station power
 

If we use a car battery or a deep cycle battery, we will enclose it with a thin layer of ABS. I believe it is quite acid resistant and we should smell the sulphur before anything bad happens. Also, I am trying to eliminate most of the wiring by placing it on PCB.

Re: Driver station power
 

Dev,
Acid spills are almost the least of your worries. Hydrogen gas buildup, is a big issue in addition to a litany of other things.

Re: Driver station power
 

I agree with that. Do you by chance know how to get rid of this H?

Re: Driver station power
 

By the way, why use a deep cycle battery? Typical inverters cut off at 9.6 volts and my electronics will probably cut off at something like 5.5 volts. By that time, the control panel would have warned us to plug in the battery charger. Also, what if the cart will be plugged in while we are at our pit and run off battery otherwise?

Re: Driver station power
 

Car batteries are designed to quickly discharge at over 200 amps to start the car and then be recharged by the alternator. They are typically only designed to be discharged at most 10% of there total capacity. Discharging the battery fully will shorten a car batteries life exponentially.

A deep cycle is designed to be discharged fully and recharged over and over but cannot supply as much amps as a car battery. Deep cycles are fully discharged when they reach around 11 volts (not 0v).

Re: Driver station power
 

So how do you get rid of the H buildup? Can I just place vents. Also, I was going to monitor the battery thermally to make sure it doesn't get too hot. Could that be good enough for preventing too much H buildup?

Re: Driver station power
 

Thanks. That gets rid of some of my confusions. So what should I have the low voltage cutoff voltage to be?

Re: Driver station power
 

Isn't that dangerous? Could I mix it with oxygen and make water instead?

Re: Driver station power
 

It's not dangerous, since the quantities of hydrogen involved are very small.

That's what you're doing with a candle, using the oxygen in the air.

Re: Driver station power
 

Unless your enclosure is hermetically sealed you should be fine.

Re: Driver station power
 

Time to end the speculation. Part of the battery chemistry is sulpheric acid which is a combination of sulpher and water (H2O). When current is passed through water the eletrical bond between H and O become overcome and the molecule breaks into H2 and O. In normal cases, what molecule break naturally occurs during charge and discharge recombines as water without ever leaving the battery. However, there is always the possibility that hydrogen is vented to the atmosphere in and around the battery along with oxygen. That combination is explosive if left to buildup and is exposed to any ignition source like a spark or hot soldering iron. Remember the Hindenburg?
Deep cycle batteries are nearly identical in design to normal batteries except for a few design differences. The deep cycle has different plate design to withstand high current demands for longer periods of time and there is a deeper reservoir beneath the plates. During normal charge and discharge cycles in lead/acid batteries, some particulate forms in the solution and much of it drops to the bottom of the battery. Over the life of the battery, this particulate builds up and eventually shorts out the bottom of the plate area. This not only shorts the charge stored in the cell it also shunts charge current preventing the chemical reaction to be reversed.
As to capacity, there is no blanket statement to be made here. The amp hour specification of our robot batteries are specified to about 1.7 volts/cell or about 10 volts, depending on discharge current. However, during normal use, the voltage drop across the internal resistance of the battery can actually appear to be much lower on a fully charged battery.
We have all become complacent in handling robot batteries since they can be used and charged in any orientation. (I still do not recommend charging upside down.) Car batteries and deep cycle batteries, in general, should only be used in one orientation and never allowed to tip or turn over to prevent spills.
Now to the other dangers. Robot batteries are capable of 600 amps when fully charged. That is capable of welding metals when used improperly or not fully insulated. Car batteries are capable of at least three times that current and deep cycle batteries even beyond that. The batteries you are talking about are also much heavier than robot batteries. One of my coworkers dropped a small car battery on his foot and broke his toe.
So as you can see there are a number of issues that need to be addressed before your ideas and design is safe for all participants.

Re: Driver station power
 

Thanks, Al. That reduces quite a bit of confusion. However, when looking at car batteries, the maximum discharge I could find was 700
Amps. Also, I thought robot batteries support a maximum of 250 Amps.

Re: Driver station power
 

You have to read the spec sheet. A typical replacement battery for my car is capable of over 900 cranking amps and is rated for 44 Amp/Hr. with a reserve capacity of 100 minutes at 25 amps. Pulse currents of 50% higher is not uncommon with short circuit currents nearly triple the cranking current. So max current is nearly 3000 amps compared with our 600 amps max draw. For both batteries, this current will produce a voltage drop across the internal resistance which prevents the battery from supplying 12 volts at that load. Delivering short circuit current to four feet of #10 wire should a fault occur, will produce nearly 36000 watts. The result is burning wire, and very hot, dripping, melted insulation. To use a battery of this type requires some good circuit protection in the form of fuses and high current switching. I have seen high currents fuse the contacts of a switch preventing it from opening the current flow.

Re: Driver station power
 

Cool. I didn't know that 3000 amps could be drawn from a typical battery. I would think that the battery would melt, the terminals might evaporate and there would be a big explosion because of all the hydrogen gas buildup. I also think that the insulation must have evaporated by then

Re: Driver station power
 

OK, brain-teaser for high school and college students:

The chemical reaction described above is

2H₂ + O₂ => 2H₂O

Notice there are three molecules on the left, and only two molecules on the right. So why is it an explosion? Why not an implosion?

Re: Driver station power
 

What about a simple small brushless fan to vent the hydrogen outside and allow the outside air inside? Probably no spark will exist in regular open space, unless the building is struck by lightning. So, after a while, the hydrogen would have diffused and possibly even turned into water. Also, how much H is even produced by a battery running at full capacity?

Re: Driver station power
 

What you didn't mention is that the process involves a significant amount of energy transfer.

In order to go from Hydrogen and Oxygen to H20, quite a bit of thermal energy is produced. Hydrogen and Oxygen, mixed with an ignition source like Al mentioned, would create a combustive reaction. An exothermic reaction, like this one, would be considered an explosion. :)

Do I get Ether points?:D

Re: Driver station power
 

Not quite yet...

A sealed steel tank contains a pure stoichiometric mixture of Hydrogen and Oxygen at ambient pressure and temperature. The tank is capable of sustaining very high pressure without damage or deformation. There is a spark plug protruding into the tank, as well as a high-pressure-fast-response pressure sensor.

The spark plug is ignited at t=0, and the pressure vs time is recorded. Assuming the steel tank does not burst or deform, and the pressure sensor accurately records the pressure, describe qualitatively what the pressure data looks like from t=0 to t=10 seconds.

Re: Driver station power
 

I remember this from 8th grade. Basically, there woll be a decent amount of potential energy that will be converted to heat. Basically, there is a sharp peak ad then the energy reduces down to zero. I believe that the deformation and pressure would be similar, as water as a liquid would probably have a lower pressure. Am I right?? :P

Re: Driver station power
 

My favorite answer to the question actually involves E=mc^2...

Re: Driver station power
 

There are only 2/3 as many molecules after the combustion as before, but they are *much* hotter. This increased temperature of the combustion product causes a large initial pressure spike¹, despite the reduced number of molecules.

However, even though the gas in the tank is momentarily very hot, its thermal mass is far smaller than the steel tank. The gas cools almost immediately, and since the number is molecules is less than it was before the combustion, the pressure drops below its initial value.

The gas will cool to ambient temperature very quickly. When it does, and assuming no condensation, the pressure in the tank would be 2/3 of what it was before the combustion.

However, because the gas is pure water vapor, the final pressure in the tank will not exceed the vapor pressure of water (at the temperature of the gas).

At ambient temperature (say 25C) the vapor pressure of water is only 0.48 PSI. This is much less than 2/3 of the initial pressure, so the pressure will cause some of the water vapor to quickly condense into liquid water until the remaining water vapor is just sufficient to create a pressure of 0.48 PSI.

¹which is why the gas would initially explode if not confined inside the sealed tank

Re: Driver station power
 

Isn't this equation just an approximation, not the exact calculation to less than a joule? Anyways, 1 kg of H fused together would probably cause ~9.0e16 J of work. However, as we know, most of this goes to heat, and that's why nuclear plants explode like atom bombs when you shut down their cooling system.

Re: Driver station power
 

No. The equation is an exact description of the equivalence of mass and energy.

Nuclear plants do not "explode like atom bombs". They melt down, which may or may not cause an explosion, but it is not a nuclear explosion. It could be a steam explosion, or combustion.

Re: Driver station power
 

If we have any need for batteries whatsoever outside of the robot itself, we always turn to the robot batteries themselves.

-We have our trailer rigged so we can power the internal lamps when we unload in the dark with no vehicle.

-Some charter buses don't have power, so we use the AndyMark inverter and 2 power strips on extention cords in the overhead bins to give everyone precious power during our rides to competition. Even at maximum inverter capacity, one battery lasts >6 hours.

-if we have to charge our driver station away from the plug, the robot battery/inverter combo is light enough (though inconveniently heavy) to tote around.

you already have the infrastructure to cycle through a battery every match and keep multiple on the charger. why not set one aside for other uses.
What advantage does a car battery have over the motorcycle battery you have plenty of?

Re: Driver station power
 

I agree, I was a bit sarcastic!

Re: Driver station power
 

There's much to appreciate in E = mc^2! Here's a link to a Wikipedia article that goes into more depth -- worth reading.

Re: Driver station power
 

I, myself, love e=mc^2, mostly because it defies physics and newton. Mass can be destroyed and energy can be fabricated. That leaves me to think, there are still some neutrons, protons,electrons, etc. Couldn't we use them to fabricate mass like gold?

Re: Driver station power
 

If you want to charge batteries on the go, I believe that a large lead acid would be much more beneficial. I do not think it would be wise to charge robot batteries with robot batteries

Re: Driver station power
 

Also, how did you get >6 hours of runtime on full load? The inverter is 200 watts continuous so 200/12=16 2/3 amps on full draw. At 17 amp capacity, you have roughly an hour of runtime. Also, that is under ideal efficiency. The inverter that I have at home requires 1 amp when powering nothing (except thin air).

Re: Driver station power
 

The post about charging the driver station (laptop) with a robot battery is a common practice and is very beneficial while at competition. It has definitely saved our bacon many times. Don't use a large lead acid. They are heavy and spillable.

I hope no one would charge a robot battery with a robot battery. This doesn't seem like a very practical approach...

The battery provides a voltage source, the devices plugged in draw a current. The current draw is dependent on the load of the device(s). For instance, a laptop at idle will consume less power than at 100% CPU utilization. Since most tasks are near-idle for the average laptop, a laptop plugged into a robot battery should last a good portion of a day.

Re: Driver station power
 

This brings up another interesting matter, so to speak -- how and where are elements like gold fabricated from lighter elements and energy? The answer is really quite something...

Re: Driver station power
 

Alchemy is reborn!!!

Re: Driver station power
 

In particle accelerators and nuclear reactors.

And, in some cosmological theories, in stars.

Re: Driver station power
 

As I work at a battery store, I can tell you this battery should suffice for one day at a time, provided you plug it into a charger each night after a full day of use at a competition.

If a less heavy battery is needed (i'm guessing you don't want to carry around a car battery all day. Trust me, it gets heavier than you would think), you can look into Shorai lithium motorcycle batteries, they weigh about 2 pounds so it would be almost nothing in a driver station, but they run ~$200 in-store, ~$100 online, depending on which one you get. Still 12V, and last longer than a lead-acid battery

Re: Driver station power
 

Just buy two 11.1 6000mah lipos and place them parallel. You will then have a 12A battery bank, lipo for under $50. You would get one of those lipos then, dirt cheap.

Re: Driver station power
 

Worth a read: Stellar nucleosynthesis. Not directly helpful for powering a driver station though!

Re: Driver station power
 

At that point why not use a competition legal battery? About the same price more amp hours.

Re: Driver station power
 

Even better: get two of the non-legal MK-ES18 "replacement" batteries off batterysharks.com or another site for the price of one legal battery. Use them for your robot in the pits, training, demonstrations, and powering inverters for charging your driver station or stands laptops.

FYI: We've tested the non-legal batteries using the industry standard tests. They are at least as good, and in some cases, better.

Re: Driver station power
 

I don't think the issue is the legal ones being better or worse. It is to ensure the robots at competition have the same energy available. The advantage of buying legal ones is you can use them at competition & don't have to worry about segregating the non legal ones. Worth the price difference to me. Although we have come across some non-legal batteries at garage sales too cheap to pass up. YMMV

BTW we are having some custom Li ion batteries built. About the same size & wt as the legal battery. Double the amp hrs. Too bad we cannot use them at competition. :)

Re: Driver station power
 

If you assemble a lipo yourself, it can be chaeper than buying it. Just buy some 5000mah cells together and you have a lipo that will charge/discharge rapidly and hold twice the power.

Re: Driver station power
 

I've always believed the case is that the MK and Enersys brands are stable (and thus have the same specs). The replacement batteries are probably made in the same factory, but the brand names and case color change by the month.

Re: Driver station power
 

Be careful when you are looking at battery specs. I looked up a few lithium ion batteries for this response. A stated motorcycle replacement 20 AH battery, can only deliver 200 amps max compared with our 600+ amps. While it has a longer life and can charge at over 10 amps, it also has a smart circuit that shuts off the battery when it falls below 8 volts. Most LI replacement batteries have some internal circuitry to limit currents or prevent unusual charge conditions. It cost $280 by the way. While our current batteries have an acidic electrolyte, the internal chemicals will not set themselves on fire when exposed to the atmosphere and do not maintain an above normal internal pressure as Li types do.

Re: Driver station power
 

As Al says this is something that needs to be well thought out. One of our sponsors packages batteries for military / industrial applications. They are doing the engineering for the battery I mentioned. As Boeing & others with more knowledge than me have found out, Li ion can be tricky.
We are using the standard 120amp breaker switch. It can flow more current than that for short periods, but it will trip.

Just recently a Telsa "hit something" and set its battery pack on fire. Much to the consternation to the FD that tried to put it out.

Re: Driver station power
 

I guess that is where a supercap is great. It will take over for the power surges

Re: Driver station power
 

What is the above comment referring to?

Re: Driver station power
 

Or a supercap can produce a surge, as in the story that was recently told here about getting zapped by capacitors in a speaker. Similar concerns with lipos -- there are hard and fast rules for good reasons, such as safety. The rules are abundantly clear and these rules have been in effect every season I've been involved: no external energy sources (there are a few very strict exceptions) and no extra parts in the power system (again, very specific exceptions such as small filtering capacitors for motors).

There are good ways to solve problems such as these within the rules, but within the rules is where to stay. Even though the rules do not apply to things like carts and driver station power, the safety concerns remain valid.

Re: Driver station power
 

The topic has digressed a bit, but it has never been about what is legal on a competition robot. That has & will continue to be controlled by rule.

Our motivation for a Li ion battery is for our tee shirt cannon which is going through about 3 comp batteries in a typical football game. We were originally going to use a deep cycle lead acid battery. One of our sponsors offered to build the Li ion battery which he says is better technology for the application. I expect cost & safety will prevent this technology from being adopted by FRC for competition in the foreseeable future.

Re: Driver station power
 

Ah, fond memories...

Back in the 60's I got knocked out by an electrolytic cap in the power supply of a Hi Fi audio power amp I was designing and building with 6L6GC vacuum tubes in push-pull configuration.

I unplugged the amp to re-solder some wires going to the 5Y3GT full-wave rectifier and forgot to discharge the caps.

That thing was a beast when connected to the triaxial 12" speaker in my home-built speaker cabinet. The cabinet was 12 cubic feet and weighed over a hundred pounds. 1.5" thick plywood internally reinforced with two-by-fours.

Re: Driver station power
 

If you guys are scared of lipos, try lithium ferrophosphate (life bateries). They don't hold as much, (by barely), but are mucho safer than lipos which explode and catch on fire veery easily::ouch:: ::ouch:: ::ouch:: ::ouch::

Re: Driver station power
 

I have to hear this one, please...

Re: Driver station power
 

That reminds me of the 5000F supercap bank that I want to fit in my room. Power inverter for AC power, and solar panels to charge up the caps. Use it to power electrical tools that require craploads of energy to function. BTW, how do you guys thing of the safety of a 12000 watt inverter?

Re: Driver station power
 

Just worked on an RCA BA6 leveling amp ca 1948. Our local AV guys found this on the shelf and had used it as a movie prop recently. They were thinking of dumping it until they looked one up on the boards and found they are going for $6K. I went over to their shop and plugged it in. I noticed that the OO3/VR150 wasn't lighting up very much and as I looked further I noticed that the the filaments on the 5R4 weren't very bright. (thinking that the transformer had shorted the filament winding) When I touched the envelope (lightly) the filaments went out. I told them they needed to get a 5R4 and call me if they couldn't get any audio through it. The 5R4 is connected to a center tapped 640 volt winding on the power transformer. The caps have bleeders in this design though. I suggested that they put the unit on a variac and run the voltage up slowly over a few hours to form the caps. They reported that worked fine and it is now making some nice sounding audio. This unit uses a pair of 6SK7s feeding a pair of 6J7s feeding a pair of 6V6s on the output, each stage is balanced during the setup. I of course told them to touch the 6SK7s lightly after turning it on to see if they were warm. I once fixed the Clarion Bells at Bradley University when a 6SK7 turned up cold during an onsite check in the bell tower of Bradley Hall. But that was 40+ years ago.

Re: Driver station power
 

Here's the story I was thinking of: "SoC Power".

Incidentally, I wasn't saying there aren't ways to do things for a cart, off-season demo robot, etc. that are outside the rules for a robot but still reasonable and acceptable, but some things that get brought up here are probably not wise paths for students to take without an abundance of caution that isn't a universal trait, because there are many more ways to get this sort of thing wrong than right and learning by experience can sometimes come at a very high cost. Better safe than sorry!

FWIW, capacitor banks power railguns and some very powerful lasers.

Re: Driver station power
 

Let us not confuse voltage with current.

At the voltages involved with FIRST it is unlikely anyone will ionize the air significantly enough to move any meaningful current.
Regardless of what is storing or producing that potential.
Physically shorting either a battery or capacitor would be unpleasant.
The capacitor will be unlikely to literally explode however a battery might pop from boiling.

Also 'supercapacitors' generally have a low voltage rating.
They also tend to have more internal resistance than what most FIRST people would consider normal for a battery.
Finally 'supercapacitors' have a much greater leakage which means that they will self-discharge much faster than your average battery.

Comparing an audio amplifier say for PA application potentially with 70V outputs to a 13.8VDC charged 'supercap' is not a good comparison.
It would be like unplugging and opening a tube computer monitor and poking around in the 15,000V+ section.
People who frequently poke around in electronic repairs learn about these risks (some the hard way).

A high voltage and capacitance bank would be much larger physically.
'Supercapacitors' are not typically suitable for rail guns or generally powerful lasers.

The real lesson for anyone doing repairs from the referenced post is to carefully consider what might store power when things are allegedly powered off. All of those things present an elevated risk.

Re: Driver station power
 

I concede the point. However, even a 5V supercap has a fair amount of stored energy that can be released quite quickly under the right (wrong?) conditions, internal resistance notwithstanding. Same goes for some batteries. I wasn't trying to imply that these scenarios were the same in all respects, only that there is danger here and these components should be treated with respect.

If anyone accidentally succeeds in making a rail gun that fits in the space / weight restrictions of an FRC 'bot (or cart, or driver station, or t-shirt cannon robot, ...), I'm sure the DoD will beat a path to their door! But I'm much more concerned that someone might get hurt because they don't appreciate what they are dealing with. If this happens, it will have been a preventable tragedy and therefore will be doubly tragic. I was just trying to sound a note of caution and also bring up some interesting devices that illustrate how much energy can be stored in capacitors.

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The moto is lighter, almost 2 pounds, so it's easier to carry

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I agree caution is always warranted.

You should qualify what sort of performance you want from the railgun because I have built such an item and it would fit within the dimensions of FRC robots. Course the projectile only achieves a velocity comparable to a air rifle. So it's more amusement than useful for the DoD. ::safety::

The capacitor bank (these were not 'supercapacitors') on that unit was actually in a box that would fit on an FRC chassis and it did at any one time contain sufficient energy to be a very real threat to human safety. It was rigged with a bleed down load specifically so that when not in operation it eventually was safe to do repairs.

An interesting project but not safe for students. Do not attempt it. Way more than enough stored energy to melt metal.

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Don't you need a high voltage to ionize the air? Also, used properly, a supercapacitor can be a great invention. I am designing a mini car right now and I might use the fast energy storage of supercaps to allow regenerative braking. Their low internal resistance will allow the brakes to have a significant effect while not getting as hot or exploding if I were to simply feed back into the 200 amp lipo.

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By the way, do any of you know the regulations for large lipos? I want to buy 4 200AH Howell (Chinese) lipos to power my electric are that I want to build These weigh six kilos a piece. I want to make sure it is legal before I order them. I am expecting them to be expensive

BTW, sorry for the confusion, but they are actually Lithium Ferro Phosphate (LiFePO4 Batteries)

Here is Howell's page:
http://www.howellenergy.com/
http://www.howellenergy.com/index/view.php?aid=4 (HW-F200Ah)

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Microcontrollers are quite fun to work with. They allow me to do rapid prototyping without messing too much with the electrical components. I will probably have an MCU controlling this driver station. What do you guys think about the Parallax Propeller (P8X32A)?:D

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I think it's quite nifty.
Nifty enough I offered to build FIRST a control system based on it.

Just wait till you see the second generation.

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Yep. Just can't wait! The 2015 Control System seems great. What do you guys think? Also, if we were to use Propeller Chips, the supply of them would get overwhelmed! However, most teams would only need one because of how robust they are. Mine has gone through electrostatic discharge, I/O shorted out and lots of other bad things. Yet, the chip works like a charm. This would only give Parallax a reason to grow larger, thus reducing their product prices!
:D :ahh: :) :] :ahh:

Re: Driver station power
 

I meant the second generation Propeller.
Parallax has more than sufficient production for the first generation for everyone in FIRST to buy several.
I checked when I answered to RFQ.

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Yes. However, Parallax is still a small company and there are many product manufacturers who use their products.
If demand increases and the supply remains constant, there is a shortage and the price goes up.
If the demand decreases and the supply remains constant, there is an abundance and the price goes down
If the demand remains unchanged and the supply increases, the price goes down. Ceteris Paribus.

:] Some economics review for me. I think it is the supply-demand curve which would give us the price after heavy load. Also, after the kickoff, many teams won't need another for a while, creating an abundance and reducing the price.
We could expect to pay $11 per chip instead of 12!
::ouch:: :D ::ouch:: ::ouch::

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Parallax has ample production to handle this load.
The cost of the Propeller is so low compared to 8 PICs or 8 AVR plus the support circuitry I wouldn't worry about it.

The key trade off with the first generation Propeller is the lack of peripherals.
It is also in some ways a positive.
You don't get stuck with whatever the chip designer may have goofed.
However you don't get the benefit of cheap integrated peripherals when you buy the MCU.

In reality Parallax has been able to support putting production volume in Radio Shack, schools, some business ventures to the point of product starting to hit surplus stores and they have past experience with FIRST in the sense that the control system circa 1997 and 1998 was essentially 2 Parallax BASIC Stamp 2 on the robot side. One BASIC Stamp 2 was tasked with the field radio tasks and the other was open to the students to do as they pleased.

In effect a single Parallax Propeller in an FRC style control system is 4 times the power and because of the way the I/O round robins it is vastly more flexible (at the small price of some enforced timing requirements that are...for this application...quite workable).

The answer to the FRC control system bid U.S. Cybernetical made would have allowed a cooperative system of one or more Parallax Propellers onto the robot. Literally to the point that you ran out of electricity. It would have been possible to literally assign cores (cogs) to functions even almost whole Propellers. Plus you could have used the Propellers on the driver's station.

When last I worked on this I had the ability to issue orders to whole subsystems in near plain English. Literally telling a prototype to: move left wheel forward at 20 RPM. Of course that was one concept.

I also have a graphical language I started creating to open source (effectively an alternative to LabView) that targets the FRC style system I laid out. However given the lack of interest from FIRST I am withholding that software until I feel it is in my interest to release it (my work, my choice).

In any event the big downsides from the Propeller are:

Lack of floating point math (has to be transparently emulated or done in a co-processor...both of which I did)
Lack of a hardware multiply (no longer an issue in the second generation Propeller)
Lack of hardware interrupts (depends on how deadset you are on hardware interrupts as they have upsides and downsides)
Lack of on-board integrated peripherals (they do have lookups for trig functions, PLL, etc)
Lack of a defacto real time operating system (in reality real time OS are often misunderstood and overhyped)
Lack of hardware drivers for say cameras (this is not as big a deal as it seems)

None of these would have prevented creating near supercomputing performance control system on an FRC robot.
The cameras could have integrated ARM processors, use a laptop, or stream to the driver's station.

One concern FIRST stated was that they felt it was too complicated for the students to understand.
Well...in truth...I find that doubtful considering the rules for FRC are pretty darn vast and complicated.

Oh and the control system with the radio was around the $300 mark when I last looked with a single Parallax Propeller at the stated retail price currently and a Turtle low frequency radio for the field communications sporting an additional Atmel AVR or Microchip PIC (locked out for FIRST's control). From there the additional ready to assemble Parallax Propeller modules were much less than $75. So really for the cost of the original cRIO you could have dozens of Parallax Propeller on a single robot. With multiple or single sidecars (the I/O to the side cards was flexible so you could redirect sidecar peripherals to one or several Parallax Propeller like a baseband network).

I didn't leave ARM out either. I made a camera module with an ARM CPU. However my design choice was that if real time OS was your ultimate demand put a laptop on the robot and plug the Parallax Propellers into that laptop. Use the highly cost effective laptop as your slave peripheral like people do now with things like the Beagleboard. The interrupt driven nature of the laptop on the robot could be easily over come into the real time domain using the Parallax Propeller to enforce timed operations where the laptop would otherwise have issues (such as monitoring an A/D converter, reading encoders...etc).

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Looking at the specifications of the propeller ii, it seems though the processor is oowerful enough for vision. Also, I believe they are adding a lot of ADCs and DACs. It will then be an entire computer

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Parallax has made several alternations to the Propeller II design the last few years. The Propeller I is already powerful enough to play an 80s classic video game and generate the 4MHz NTSC video signal with some cheap extra parts. It doesn't have a true ADC/DAC per se. It cheats using a trick similar to the BASIC Stamps.

The trick with using the Parallax Propeller (current or otherwise) for vision is to understand how to divide the tasks of the vision system into parallal operations to take advantage of the hub memory and extra cores (cogs). This is itself much more tricky then just getting OpenCV and slapping it on laptop. On Team 11 we've written vision software from the camera driver up but in 6 weeks that's a challenge. Also you start to get into calculus, linear algebra and several other mathematic fields that normally high school students are not yet all that familiar with.

Honestly the best way to overcome vision on the Propeller itself would be to get someone to 'own' the project and let them develop the extensive library of tools you really want to offer it as a 'plug and play' option.

It's possible even with the Propeller I but it's a lot of subtle work and people would be right to ask why do that work when there are other ways already cost effective to achieve the same result.

Other than the camera really the Parallax Propeller is an SVGA, keyboard and mouse capable computer already.
See DEFCON for a fine example:
http://dangerousprototypes.com/2012/...lax-propeller/

All you had to do was solder on the HD-DB15, a PS2 keyboard and PS2 mouse connector and you have a 'PC'.
As you walked around they even talked to each other (it was part of the fun...you needed the rest of the badges to solve the puzzle).

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I guess.
Anyways, here is the feature list. Pretty Impressive with the 1200 MIPS!
http://www.parallaxsemiconductor.com...ropeller2specs
:yikes: :yikes: :yikes: :yikes: :yikes:

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So, I have been tinkering with the CAD of this cart. What drivetrain would be best?

Manual:
Castor
Cart
Something Else (Please comment it)

Motorized:
Swerve
Cart
Mecanum
Other Holonimic (Omni, etc.)
Locking Mecanum
Legged (Seems quite impractical!)
Something else (please comment it)

Also, for control, what should I use?
Gaming joystick
xBox/vex type joystick
Arrow keys on computer
Buttons
Pressure sensors
Brainwave
Eye tracking
Mouse
Spring-loaded potentiometers
Pot Handlebars
Levers (Hand)
Levers (Foot)
Autonomous (Quite impractical)
Something Else (Please Comment it)

Also, what do you guys think of the idea that the driver station docks onto this battery cart? Do you guys like it, want me to trump it or want more info about it?