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.