Rules Change I Would Like to See - Batteries

[frcguy]

Originally Posted by ASD20

It is already possible to power a Raspberry Pi off of a robot. You just need to wire the power cable to the 5V/2A port on the VRM. My team used it this year for our vision system and it worked just fine.

+1

[asid61]

Allowing 12v to 5v regulators would be a lot more useful in my opinion. There's not need to have a separate battery when you can just step down the PDP voltage.
Sometimes the VRM doesn't have enough power to give. Even the 5v 2a slot isn't enough for some applications, and I dislike the extra loose wires that it requires. Ultimately though, there's not enough need for more 5v power to make it worthwhile imo.

[Ty Tremblay]

Originally Posted by asid61

Allowing 12v to 5v regulators would be a lot more useful in my opinion. There's not need to have a separate battery when you can just step down the PDP voltage.
Sometimes the VRM doesn't have enough power to give. Even the 5v 2a slot isn't enough for some applications, and I dislike the extra loose wires that it requires. Ultimately though, there's not enough need for more 5v power to make it worthwhile imo.

DC-DC converters are legal.

[GeeTwo]

We have also used automotive USB power converters to power USB and other 5V devices on both our competition and non-competition robots (e.g. t-shirt cannon); you can get these at almost any local convenience store. (Example). It is usually a simple matter to remove the power port connectors and expose the wires to provide the 12V input. There are also units with wire pigtails or spade connectors for inputs, designed for installing in a dash board; a bit more effort to locate, but neater-looking.

[Michael Hill]

Originally Posted by GeeTwo

We have also used automotive USB power converters to power USB and other 5V devices on both our competition and non-competition robots (e.g. t-shirt cannon); you can get these at almost any local convenience store. (Example). It is usually a simple matter to remove the power port connectors and expose the wires to provide the 12V input. There are also units with wire pigtails or spade connectors for inputs, designed for installing in a dash board; a bit more effort to locate, but neater-looking.

I would suggest against a USB converter because you're really only guaranteed 500 mA. Odds are it can actually do more than that, but something to watch out for, especially if you're doing anything computationally intensive on the Pi. I'd also watch out for some of the cheaper automotive USB converters. The power is often really ugly (lot of switching noise), which is generally fine for charging your phone, but for a Pi, it may be a little more sensitive to switching noise.

[David Lame]

Originally Posted by Michael Hill

I would suggest against a USB converter because you're really only guaranteed 500 mA. Odds are it can actually do more than that, but something to watch out for, especially if you're doing anything computationally intensive on the Pi. I'd also watch out for some of the cheaper automotive USB converters. The power is often really ugly (lot of switching noise), which is generally fine for charging your phone, but for a Pi, it may be a little more sensitive to switching noise.

Thanks for illustrating the issue very well.

Yes, there are ways to do it, and lots of teams do them. However, there are issues with them. Gotchas. Things to look out for.

If the students were just allowed to use devices that were actually designed specifically for providing power to a device that was specifically designed to use that power, those gotchas wouldn't exist.

Again, some people might look at that as a good thing. Providing an easy solution is not necessarily the best thing for a FIRST team. The question that the rule makers have to ask themselves is whether they want to encourage people to make use of the fancier processing available through the use of coprocessor boards. If so, do they want to make a little bit of electrical engineering a prerequisite, or do they want to let them cut straight to the processing part, assuming they are willing to pay a small weight penalty. (I would assume that, unlike the main battery, any batteries used to power auxiliary computers or sensors would count against the robot weight allowance.)

I don't think there's a "right" answer to the question. I have an opinion on the subject, obviously, but I won't say that there is an obvious answer.

So far, though, the people providing information haven't really discussed advantages and disadvantages, just that the rule change isn't necessary because there are engineering solutions available for teams under the current rules. I suppose the disadvantage is that it introduces an unnecessary change to solve a problem that, in many people's opinion, already has an adequate solution.

[asid61]

What would you define as a dedicated USB power source? The powerbanks for phones are one example, but those have a non-negligible power storage compared to the robot battery itself. One can simply use a larger DC-DC regulator to get bigger 5v power.

[David Lame]

Originally Posted by asid61

What would you define as a dedicated USB power source? The powerbanks for phones are one example, but those have a non-negligible power storage compared to the robot battery itself. One can simply use a larger DC-DC regulator to get bigger 5v power.

What I have in mind is the powerbanks for phones. The exact wording is something I would leave for the rule makers.

Sure. You could use a DC-DC regulator. It's not that hard, but it requires either a student or mentor who understands the requirements, and a little bit or rewiring and cable cutting to hook the output of that to whatever the coprocessor board requires.

It just means that a programmer who wants to do some cool programming has to team up with someone who understands how to get an adequate amount of 5 volt current out of the available power sources. A student whose focus is programming, and who knows nothing about electricity and power supplies now depends on having someone else on his team that can take him past the "easy" step of finding the appropriate regulator.

Not that that's a huge deal, but on smaller teams that might be the thing that prevents the budding programmer from making it happen during competition season.

One thing that I have seen, both in my professional career and in FIRST robotics is programs stalled because the person assigned to the task knew how to do the "hard part", but not the "easy part". Just last week at the office, I had to coach an expert Java programmer through the arduous task of reading a voltage from a device. We have been working on automotive diagnostics via Canbus. She knew everything possible about networks, communications protocols, and data structures, but we had a new task to mix in voltage data read from a data acquisition device. She knew everything about how to write the program, but she was utterly perplexed about where to connect the wires, or even what to connect them to.

I've seen it happen in FIRST as well. The electrical people can't do anything because they can't write a two line program. The software people can't do anything because they can read the sensor, but they can't connect it to a power supply. This proposal just makes it easy to get over that hurdle.

Whether or not that is a good thing is a matter of opinion.

[ASD20]

Originally Posted by David Lame

What I have in mind is the powerbanks for phones. The exact wording is something I would leave for the rule makers.

I would guess that $5 noname chinese usb battery packs off of Amazon are exactly the type of thing the GDC has created so many electrical rules to ban. Unless they only approved a few specific models, regulating something like this would be a nightmare. Not to mention the 5V/2A isn't even enough for many computers. Odroids (5V/4A) and Jetsons (12 or 19V ??) come to mind.

[Peter Johnson]

Originally Posted by ASD20

I would guess that $5 noname chinese usb battery packs off of Amazon are exactly the type of thing the GDC has created so many electrical rules to ban. Unless they only approved a few specific models, regulating something like this would be a nightmare. Not to mention the 5V/2A isn't even enough for many computers. Odroids (5V/4A) and Jetsons (12 or 19V ??) come to mind.

Exactly. There are safety concerns as well given the prevalence of lithium ion chemistry batteries. You do NOT want a large one of those punctured or shorted. Cell phones and Kangaroos have pretty small batteries, and laptops are typically above the $400 cost limit (or considered too heavy). Punctures in even small LiPo batteries can be quite destructive, and a large lithium ion battery on a FRC robot sounds like a really bad idea when DC to DC converters (or doing vision processing on the driver station) are perfectly viable alternatives.

[Jaci]

While we're at it, I think it's worth a mention that you are allowed up to 3 Additional VRM units on your robot according to R48 of the 2016 Manual. If you do have a processing unit on your robot that requires more than 2A (but less than 20 due to the fuse on the PDP), that is a possible option. As many others have mentioned, DC/DC converters may also be of interest.

Honestly, if you have a processing unit on your robot that is constantly drawing more than 2A, it might be a good idea to ask yourself "is this worth the trouble?". Something to keep in mind that electrical engineering, especially on a mobile robot, usually has the challenge of working with the power you're given. FRC Robots have a pretty big supply of power going to them as is, do we really need more?

[GeeTwo]

Originally Posted by Michael Hill

I would suggest against a USB converter because you're really only guaranteed 500 mA. ... The power is often really ugly ...

Many of the 12V converters feature a 2.1A port and a 1.0A port, which is enough for a pi. You can always add a couple of capacitors (it's a custom circuit) to clean it of if necessary. Our preferred method is still the VRM or other robust, regulated DC-to-DC converter. Jaci's bottom line is right on the money:

Originally Posted by Jaci

FRC Robots have a pretty big supply of power going to them as is, do we really need more?

Remember, in addition to the battery, we can (in most recent years, anyway) have pre-charged pneumatics tanks, pre-wound springs, and gravitational potential energy. (R35 A, C, and B respectively in 2016.)

Finally, If you really want that separate USB battery-power, charge up an old laptop, and power your pi off its USB port. There's no rule that says you have to turn the laptop on, much less do any processing on it. If you can use a classmate from a KoP, you won't even have to list any dollar cost in the BoM.

[FrankJ]

As I see it. The problem the second battery solves is not losing your sensors and CPU from brown outs. The old (pre 2009) control system had a battery for this purpose because a brown out would cause a loss of control without disabling the robot. A second control power battery Powering the Rio and radio along with other custom circuits would solve a lot of issues. It would also add cost and complexity to the robot.

Would another possibility for the auxiliary processing be the android system used in FTC? The come with batteries and meet the COTs definition.

[GreyingJay]

A cool idea, but I think the VRM (or a second or third VRM as needed) would do the trick.

We powered a Pi and an IP camera (and its LED ring light) off the VRM on our competition robot. On our practice bot, where we were a little less, uh, picky, we plugged the Pi into the USB port on the RoboRio.

[Joe Ross]

Originally Posted by Jaci

While we're at it, I think it's worth a mention that you are allowed up to 3 Additional VRM units on your robot according to R48 of the 2016 Manual.

That's not what that rule means. It gives you permission to break the one wago one load rule with up to 3 VRMs. It doesn't limit you to 3 additional VRMs, you could have as many as you want limited by the number of 20amp breaker slots there are * 3 VRMs.