I purchased some of the Arduino hat boards from SimpleFOC and now im trying to figure out how I will power my project.
Background: I’m building a robot that will have a Jetson Nano brain. It will be rather lightweight (like 1-2 lbs maybe lighter), and it will only run on carpet and tile indoors. The SimpleFOC board is definitely overkill for me but I really want to achieve a high level of control for my little robot.
I would like the charger and batteries to be integrated into my robot so I was looking at boards like this and this
the later looks smarter but the former looks like its made to charge and regulate some power.
I was also wondering if I could just use a usb battery bank if it has PD out? There are break out boards with pd triggers on them available for cheap.
Does anyone have some suggested readings I should look at on batteries? My questions are all over the place because I totally don’t know anything about using batteries like this.
Powering and managing power for the robot is always a big topic!
I suggest you look in your local RC-store at different drone components. This is a solved problem for the drones, and there are various power distribution boards.
A basic question is how big your robot is. If you can fit a regular off-the-shelf charger into it, then you will be finished with this topic in a flash, and it will be safe and reliable.
If you need to roll your own, because you can’t fit a finished product, then the type of thing you linked will work. You’ll need the right charger to handle the battery pack you choose i.e. a 2S charge module for 2S battery pack. It should have undervoltage protection and automatic charge regulation, and balancing of the cells if possible. And you should choose an Amperage that will charge your battery back in a sensible amount of time.
If you give a bit more details about the size of the robot, motors, expected voltage and current, then I (or someone else here) can be more specific in terms of advice…
I’ve got an imax b6 battery charger (probably a clone). Here is an random ebay listing:
There are a few variant - inbuild power supply, external power supply, no powersupply - I went for the latter as I have a bench PSU that I use to power it.
The above charger can be used with a lot of battery types. I’ve got a couple of 24V batteries that are similar to these:
24V might be overkill. I often find 12V easier/safer - depends on what you motors need really. The battery linked has low capacity (1300mAh) but I reckon it’ll keep you project running for 30mins. Don’t let voltage drop too much or you’ll damage battery.
Can you use PD power bank? Perhaps. As you said - you’ll need one of those switchers in order to trick it into delivering higher voltages. The yellow batteries linked above will deliver 30A whereas I imagine PD power bank might deliver 5A which I suspect is plenty.
Yes, that’s important unless you like paying for new batteries. What this basically means for me is that I measure and monitor the battery voltage (a simple voltage divider made with 2 resistors will do) and shut down the motors before it goes too low.
A USB powerbank is a great choice, I think, if it fits your power budget in terms of amps. You can step the voltage up using a readily available boost converter, although again, you need to watch the amp ratings to make sure it can handle the load. But the USB power bank is a finished module with all the protections and charger already built in, in a small form factor. All you need is a USB power adapter to charge it. You don’t even need to worry about monitoring the voltage since it will have under-voltage protection built in, and just shut itself off.
USB C PD won’t (necessarily) need a step up as it can deliver 5, 9, 15 or 20 volts. The device you plug in negotiates what voltage it wants but you can by a dongle to select voltage. Never tried it myself
a 1-2lb robot for indoor use will be quite small. So I’m just going to guess you don’t need super-big motors.
A USB Power-Bank could be one solution, but probably you’ll want to run the motors closer to 10V than to 5V… so then USB-PD or a boost module could work for you.
If you’re buying RC-batteries, then 2S or 3S is probably about right. The ‘S’ means how many cells are connected in series. Each cell is 3.7V (or 4.2 for some battery types), so 2S is 7.4-8.4V and 3S is 11.1-12.6V. That’s probably about right for a small robot.
RC Batteries are rated in terms of Ah (or mAh) for their capacity, and “C” in terms of their performance.
A 1000mAh battery can deliver 1A for 1h. The “C” rating determines how fast you can discharge and charge it. It means how much faster than 1x can the charge be taken out/put in, and you relate it to the capacity. So a 1000mAh 25C/4C battery can be discharged at 25x1000mAh, or 25A (for about 2.4 minutes), and charged at up to 4x1000mAh, or 4A, which will fill it in 15 minutes.
For your robot size, maybe 2A max current is reasonable, per motor?
So motors would need at most 4A. How much power does the Jetson Nano want? Yikes - looks like up to 6 Amps!
Anyway, you would not be running either the Jetson nor the motors at full power the whole time, so its reasonable to assume some lower average consumption values, and size the battery accordingly. But you have to size the power-components to handle the maximum current.
Making the battery swappable and getting 2 means you don’t have as much waiting time when it runs out, although I fully understand the attraction of having an integrated charger - you can always make 2 robots to solve that problem
I reached out to the maker of the LiPow earlier today and they answered some of my questions. It seems that I can charge the battery while getting power to the devices. so thats great. I actually already ordered one so I will let you all know how that works.
I also already ordered this battery I didn’t really want to go any larger but that could change.
This is going to be a long term project so its ok if I only get to do some testing before I have to wait to recharge… but the main reason I wanted the charger on the bot is because it will eventually need to charge itself.
it looks like the LiPow should protect from some voltage drop… ill have to read into that and make sure.
@runger I don’t know how much power I will be pulling from the motors yet, I ordered the small one listed on the main site.. The robot will be a sort of mop so I imagine ill be moving quite slow. I don’t even know what type of gearing I will be doing yet but I am going to do what I can to keep it very low power. Im hoping to use less than 2A per motor but idk what’s possible yet.
Oh one more question! I could only find 11.1v batteries but I didn’t want to go below the 12-24v that the docs mentioned for the simpleFoc boards… Is 11.1v acceptable for the drivers?
Your early link was to a 4s battery which is nearer 16v. A 3s will be ~12.6V fully charged and I’d recharge it at about 10.5V to avoid damage. From memory, I believe SimpleFOC board can work down to about 6V but it’s probably happier with 8+V. So 3s batteries are fine.
Hard to tell from the ebay link… they don’t tell you the motor’s resistance. I’ve got small motors similar to that one with high ohm and low ohm windings, so you’ll just have to measure when you get it.
Be sure to set the current_limit on the motor if the resistance is low-ohm!
Either way it will mean you’ll have to size things for the case when the motors are stalled - i.e. consuming maximum current, since this is very likely to happen to a mopping robot as it encounters some obstacles. But in free movement, the current will be much lower than when stalled.
Oh so the number on the battery doesn’t mean what I thought it did lol! I will need to do some more reading on lipos before I plug anything in. My complete lack of knowledge on them is concerning me.
The project will be completely open source so if it goes well you can totally have one.
Im a computer vision engineer and I want to use my experience to make something that makes peoples lives easier. The end goal is to have something that can get its own water via a bypass on the water line to a toilet and then spit the dirty water out into the toilet bowl when its dirty water bin is full. I want the mop to eventually be as small and cheep as possible, if it takes a week to clean a whole house thats fine… kinda like how the painting crew on the Golden Gate Bridge start all over again as soon as they finish!
For now im just focusing on making a toy like rover so that I can get some experience with the motors and batteries.
I’m also working on toy-like rovers, though I don’t have such a cool useful goal in mind… I’d be super-happy to exchange information if you’d like. Its a hobby for me, so I’m afraid my development speed is very slow, as I balance work on it with the real job and the family.
I currently use LiPo battery packs much like the one you got, but a lot smaller - my robots designs, such as they are, are quite small so far. The technology is the same though.
As I mainly experiment with the motors right now, a lot of the work is actually powered by a bench top power supply. On the robots I use the LiPos, and I currently unplug/plug them to charge them. There’s a certain safety to doing it that way, LiPos have never caused me any trouble, but in theory they can explode and cause fires if used incorrectly.
The plan is definitely to integrate everything on the robot, including charging and power management. I’ve spent a little time reviewing available modules, and there are quite a few things you can use in terms of BMS (battery management systems), buck/boost converters, etc… But wiring them all up in a satisfactory way, current capacity for BLDCs and things like back-powering USB-ports are issues.
My plan is to eventually develop a small power distribution board which integrates charging and data via USB-C, and safely connects the other components in way that lets you program the MCUs, use the motors and charge the batteries all at the same time.
But since that is really a second-order concern compared to the actual robot, its software and how it moves, I’ve put it on the back-burner. Instead for now I use plugs (JST or XT30) and just plug and unplug. It also means I can charge one battery while using another, and easily share batteries between prototypes during development.
Toys are both cool and useful in my opinion! I definitely would like to exchange info on the projects. I’ll be making blog posts and/or some YouTube videos at some point. Im doing my best to document my questions and the answers I find as I go because they might be useful for other people new to driving motors.
I agree about the batteries being a second-order concern but for me it would have been a non-starter if there was no way to eventually handle charging onboard. I didn’t want to start on the project if I could never finish it as a completely autonomous solution.
