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How to power Mini-PC on robot?
Hi,
We have a mini-pc that we would like to use for some advanced image processing that can only be done on a full-fledged mini-pc. We wrote the code and tested it and it works great. Now the problem is powering it on the robot. On the AC-DC converter, it states that it outputs 19.5V @4.62 Amps. We found a 19V 5A adapter, but unfortunately, when we plug it in, the mini-pc beeps and gives a red light indicating that the power supply isn't good enough, likely due to the lower voltage. Has anyone ever done anything like this, or does anyone have an idea on how to properly feed 19.5V to the mini-PC? Also, what are the rules regarding use a DC-DC converter? Thanks a bunch in advance! |
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R07, in the blue box letter I, forbids custom circuits from producing voltages in excess of 24 volts, making 19.5 presumably legal. If you can't find a 12V to 19V converter, I would recommend trying to find a 12V to 24V converter, then regulating it down to 19.5.
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I'm told R49 is now in place because someone had a 12V to 120VAC inverter on their robot as their solution to a problem like yours. Kudos to you for not trying to electrocute your inspector! What brand and model of mini PC are we talking about here? I just googled 19.5V car charger and came up with come likely candidates. I know for a fact that many laptops have an extra pin that transmits data about the charger so the laptop can be certain the charger is "safe"*. This may be a similar issue. On this I'd be concerned about is how your mini PC is going to deal with riding on a robot. The advantage of raspberry pis, kangaroo pcs, etc. is that they're solid state and generally very compact. There's not much inside to get jarred loose and bounce around. Are you sure your miniPC is going to put up with a headon collision with a defender? EDIT: Here's an adjustable DC boost converter that should work. Though it suggests you'll need a fan on it to pull 5A. While you're at it, have someone print you a case for it, or it's unlikely to pass inspection. |
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We are really conveniently in the durability of our mini-PC. It will be mounted using the VESA mount on the back and maybe a couple of zip-ties just to be sure. It has an SSD so there are no moving parts inside the computer. |
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Something like this should work nicely and is perfectly legal on the robot: http://a.co/7VNpilJ
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Meant to put an asterisk on that "safe". "Safe" in this case means both that it puts out enough amps, and that it's the correct brand, etc. Third party chargers don't work on Lenovos, for instance.
But I digress. What does the plug on the end of your AC adapter look like? Is it just the sleeve and barrel, or is there a pin in the center of it as well? Post a picture of it, if that didn't make sense. EDIT: The rear view image of that PC on the web doesn't bode well. It looks like the power port wants a center pin, which carries that ID information, which, while spoofable, is pretty difficult to spoof. EDITx2: Since it looks like you need that ID pin, you're back to first or third party laptop chargers. this might work if the OD of that connector is right. I'm afraid this is going to be a little hit or miss to get this working, though. Can you post the model number of the stock AC-DC adapter? If it can be matched up to a corresponding laptop, then you just have to find a car charger that's compatible with that laptop. |
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I will post a picture tomorrow of the official charger brick. Hopefully, we can figure something out. Thanks for the help thus far! EDIT: Now that I think of it, I believe there was a third white wire when we stripped of the connector to test with our DC-DC adapter. Maybe we just have to apply a certain voltage on that wire and it will work? |
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IMHO, you should really be thinking laptop with a built in battery.
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However, it is up to all of the LRIs with how they interpret the ambiguously worded rule about COTS device batteries. I know how I'm interpreting it until I'm told otherwise at an event by an LRI. And based on Al's comments in a prior thread, as long as the COTS computing device's batteries don't interface with the control or drive systems for the robot, you should be following the intent of the rule in his eyes. EDIT: Or don't test the rules and just use one of these after adjusting the output voltage: http://a.co/gd9yFkM |
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R37 says: "batteries integral to and part of a COTS computing device". There have been many discussions about batteries and the Raspberry Pi. Until someone sells a Pi COTS with battery, the Pi cannot have its own battery. Team 4480's computer is no different. Hence a laptop (notebook, chromebook, pad, etc.) with a built in battery is the preferred solution. Just because you have an Operating System on your COTS computing device that does not like a random shutdown is not an excuse. If you had a more fault tolerant OS (and a fast booting one), you would not "need" the second battery. |
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Q&A was asked a direct question about allowing replacement batteries for COTS devices and they chose to answer by explaining that integral means "essential to completeness". You are picking and choosing what that means (Just like I am... see the problem YET?!?!)... and if you're an LRI then you are entitled but no one else is. |
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If they are going to allow batteries for laptops then I truly do not understand why they think laptop batteries are integral. They are not required for a laptop to function. They are not essential to completeness yet that is how they defined it so I'm left to think that a battery must be required for a laptop because if it loses power then it will potentially corrupt the OS or files. Any 1st year EE undergrad can tell you that a power source is a power source yet FIRST doesn't seem to think that. Maybe a cell phone has a battery that is literally required for completeness but that's not strictly true either. All of these devices can be run from an alternative power source like the robot battery. Now they've said that USB power packs shouldn't be considered integral. Well, ok... what about this: https://www.sparkfun.com/products/13896 IT USES A USB BATTERY PACK!!! Not to mention the custom circuit rules which allows for other things like this: Ebay link for a supercap based system that should be able to charge from the robot battery USB batteries aren't legal but yet this thing seems perfectly legal provided it charges from the robot battery and doesn't power anything on the robot's control system or motors. IT MAKES NO SENSE! It's not a battery after all, it's just a bunch of capacitors in a custom circuit. Bonus, it has a built-in USB port. I'm committed to kicking and screaming about this for as long as it is ambiguous and believe me, we'll push boundaries on trying stuff. I really implore FIRST to stop and think about what this rule is trying to accomplish and then explain the intent. At this point they are just being silly. |
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Marshall, I think you're reading too much into the Q&A ruling. It specifically says that "laptops are designed to have a battery" - even if the battery is swapable, that doesn't mean you're constrained to the one that originally shipped with the laptop, so long as you use a battery intended for use with that laptop by the manufacturer.
But I can't see a way to interpret that ruling to allowing batteries to be added to a computing device that is designed to be run off wall power. Before you try that route, ask a direct question on the Q&A, otherwise you're likely to be disappointed at competition. |
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I'm already disappointed... nowhere to go but up from here. |
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Q138 was intentionally worded to be extremely broad, don't deny it. Any attempt to give a detailed response by the GDC would have likely opened up loopholes for teams to exploit. Instead, they gave a simple response that most people can conceptually understand.
Q284, on the other hand, was an extremely straightforward and narrow question, and as such got a straightforward and direct response. Be more like Q284. |
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I'd like to see one of two things: A) Say that teams can use batteries for computing devices provided it is done safely and doesn't interface with the control or motors for the robot. This can be demonstrated by having the team turn off the robot and see what is still running. or B) Make the only legal source of power on the robot to be the ROBOT battery. |
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I understand what you want, but the rule is not written that way. That certainly could change in the future, but there's a whole world of safety related stuff that has to be taken into consideration.
If a team is improvising a battery and power system for a computer, do there need to be rules around wire gauge and breakers for that system? Do we need to check the system for grounding to the frame? Do wires have to be properly color coded? It's a whole can of worms you would be opening up here. Allowing integral batteries solves that problem. GO PRO cameras can use their integral batteries without worry about burning up wiring or shorting out. Laptops can use their integral batteries while avoiding those worries as well. So, FIRST really has a choice... have a rule written like it is in order to ensure batteries for COTS devices are implemented safely, or add another section to the rule book and another dozen rules to regulate what teams can and can't do. Personally, as an inspector, I prefer being able to rule on this simply without having to dig through a bunch of different rules for a situation that doesn't really come up all that often at events. |
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Also, S03 already covers unsafe robots. |
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You would NEED rules just as complicated as our current power distribution rules for custom circuits if you allowed improvised powering of custom circuits from random batteries. For the sake of safety there just isn't any way around that. |
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I think it's vaguely clear that by "integral", they mean, like, the battery isn't an external device that plugs into the power supply port in lieu of a regular power supply. A laptop not only has a cutout for a battery, but a port purpose built for its use, and hardware integral to the laptop to regulate its charge. I think it's not THAT hard to understand the Q&A on this.
All of that being said, I think the rule is stupid and pointless and has no business making this distinction. USB batteries for custom circuits should be allowed. I know they aren't, so I won't use them, but they should be. It's silly that they aren't allowed, and it arbitrarily makes some solutions (more expensive ones!) better than others (more accessible ones!). Rules for USB batteries don't have to be complicated. Allow a USB powered custom circuit to connect to it using standard ports and cables only. Make it like pneumatics where you can't modify the cables or the battery or use custom wiring or whatever. Maybe even regulate the size of the USB battery if you must. This is not prohibitively difficult. |
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Pre-Edit: Don't read any subtext into this. If you think it's an attack on someone, it's not. Seriously, I'm not that subtle. |
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I believe I understand the spirit of the goal with this rule - but I disagree that integral batteries insure proper engineering and external batteries are more risky. If it's down the bare legal issue of having someone to sue - consider that most companies DO NOT recommend mounting their systems on a mobile robot so in a Court of Law they'll pull that out as a defense. Unrelated to the quote above: I disagree that a small PC that is not a laptop will fair poorly on a robot. I know of several HP Pavilion models (550 for example) that are miniITX motherboards in unusually large cases and take 19VDC power in. With the addition of a cheap SSD these would be no more likely to fail than a laptop and that style board is often mounted in large full size motor vehicles. Granted a full size motor vehicle has a suspension. Years ago someone told me on Chief Delphi that a laptop on a robot would fail if it wasn't as robust as a Panasonic ToughBook so I put a Dell Mini 9 (SSD) and a Gateway netbook (with a HDD replaced with an SSD) on a robot in a box merely padded with foam and drove it over the 6" bumps in the field that year hundreds of times without a single failure of any sort. Could it fail - sure. Did it fail - no. I have watched people drop average HP and Dell laptops down stairs in a padded case in hibernation and they come out in one piece and still work. As far as how to produce reliable power for such a setup - I strongly recommend that someone boost their input voltage from the battery as high as they are legally allowed then buck it down to whatever voltages they require (use switching power supplies). If 24VDC is the maximum (likely because of the history of the cRIO) then go as high as that. If you don't do this you'll always have risk that the battery will absorb a heavy load and drop output voltage just enough to force a reboot. If would be better if your PC could run off 16V or less because at 19VDC you only have room for the input voltage to dive about 5-6VDC before the only safety you have to insure a correct output voltage will be the temporary charge of the internal switching power supply capacitors. Finally I am still game to produce a 3D printed or laser cut case with a Raspberry Pi and battery in it but the requirements for this are more about FIRST rules than some huge business opportunity. If someone wants to put the work in I am will to provide assistance if asked. I figure the goal should be to provide such platforms for a bunch of common FIRST coprocessors because frankly - many times the coprocessors in FIRST are each powerful enough to run a mobile robot outside of FIRST and there could be some opportunity there if that business later provides expanded I/O solutions for those platforms as well. If someone designs the case I have access to many 3D printers and the large format laser cutters at NextFAB in Philadelphia. I can also provide free web services and domain registration to reduce the operation costs. I can finally provide testing and prototyping for the electonic elements. As I have effectively made this offer for this 5 times now on Chief Delphi alone - please be aware that you'd be working on something for next year because this year is cutting it very darn close and if FIRST (understandably) asks for something to examine themselves you are leaving them far too little time to complete that evaluation. |
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I initially saw the rule (COTS device with Battery) as a power limiting concession, but can also appreciate how it is a safety issue (did the team design the power circuit correctly).
A COTS device that includes a battery is an easy bright line to enforce. If you allow teams to install any battery, then what are the rules on what can get a battery? If a fire starts because a custom battery circuit shorted out, how do you turn it off? I'm surprised that Samsung 7's weren't banned. |
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People aren't asking for "any battery" to be legal, just USB batteries of some shape or form. These are common devices, with a known output plug, voltage, and current. A restriction saying "COTS batteries that output 5V power over USB at 2 amps or less and 10,000mAh or less" for example would be reasonably narrow, wouldn't result in these strange nightmare slippery-slope kids-wired-a-battery-at-home-using-bare-copper scenarios people keep jumping to, and would fix this and many other problems. |
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Wow, 3 pages of replies to the poor guy that needed to source a weird power supply for his mini PC. He must be getting lots of help, I probably don't even need to... Oh.
So team-4480, have you gotten any more info on the stock power supply? I'd love to help you figure out an off the shelf solution for powering that. |
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I did some searching on bypassing the "smart power plug" and there are some people suggesting that it has been done just to wire in a 2K resistor to the positive side and a capacitor to the negative and feed that into the white wire. Apparently, that white wire wants something like 12-13V. |
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At any rate, this car charger will probably work. It's listed as compatible with the same laptops that your stock charger is compatible with. It has to be a boost charger of some sort, though there isn't a guarantee of how low an input voltage it'll work with. Still $20 for a potential off the shelf solution seems reasonable to me. |
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Also, the charger states it can go from 11.5V to 15V so it should work no problem as long as we have a full battery. Or maybe it may be worth to get booster to 14V just to be sure....we will see after actually testing it on the robot. Thanks! |
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The charger might be specifying 11.5V just because that's an expected auto electrical voltage. Maybe buy one of those giant 6V lantern batteries and hook it up to that and see if it still puts out 19.5V? If not you might need a separate DC-DC that can boost 6V up to 12-14V. Which is starting to sound complicated, but I'm not the one who chose a PC that needs a smart pin power supply... |
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