Hi folks,
I am in the final part of planning the first stage of a project. I want to make a goBilda Outlaw and have a solar panel that can provide power to it. I know I have to be careful about selecting the battery types and use something to allow it to be charging the battery as well as using the power. I am also aware that the motors can use a decent amount of power. The battery will also power a raspberry pi or 2 with associated sensors etc and a Pico for controlling the Outlaw. Unfortunately, I am good with a fair bit of this, but electronics is not my strong area. I know that the solar panel I have can produce 24V and I think the motors use 12V.
If anyone has any advice that they can assist with, it would be extremely appreciated. I am really looking forward to some retail therapy and then getting to play with it all 
Karen
You can charge and discharge a LiFePO4 battery at the same time, as long as the current from the solar panel isn’t higher than the battery’s charge rating. MPPT controllers regulate this.
Hey @Karen107000,
We should be able to help you out with this. Would you be able to give us a list of all the components that are going to be powered by this battery? If you can give product names or links, that would also be really helpful.
Some battery charging modules exist that allow for charging and discharging at the same time. My concern would be choosing a battery that can handle the load placed on the system of all those components.
Would you be able to tell us more about the components you have already decided on?
Hi,
Parts are…
Pi Pico
2 Raspberry Pi’s (4B’s not sure of RAM)
Probably a camera on one of the Pi’s, A GPS module or HAT
I think the big issue is the motors with having enough juice to keep them going properly.
Karen
Thanks for those links @Karen107000,
It looks like the Chassis Kit includes a few of the following motor so the motor controller should be suitable for the job.
Can you tell us more about the solar panel? If it is definitely a 24V output, do you know if this is regulated or if it’s 24V in ideal conditions, with a voltage drop in a shady environment?
Those motors will be really power hungry so depending on how long you want this to run for at full speed, you could need quite a large battery!
Hi,
I will check the solar panel tomorrow and put a reply. I believe it is just 24V in ideal conditions but will check it out.
The size of the motors is why I want to get this sorted out 
I had looked at a different chassis but it lacked the size I was after.
Karen
Hi Karen,
2 Pi SBC’s might be pushing the capability of any solar power solution we might be able to confidently recommend.
I would recommend starting by speccing your power system for batteries first then finding a solar solution.
I’d recommend 1/2 of the 12V 3000mAh batteries from goBILDA: NiMH Battery (12V, 3000mAh, XT30 Connector [MH-FC], 20A Fuse, 12-20) | Buy in Australia | GB-3100-0012-0020 | Core Electronics
And a USB-Battery bank for the Pi’s, Pico.
Depending on your setup the computers will be using a lot of the juice - how long do you intend to run this for? (As in motors spinning, heavy computation)
I would liken this feat of robotics to be getting into the custom zone, where you are purchasing and building your own accumulator to suit your project. I’d check out some of the setups used in the Robot X competition: https://robotx.org/
And RoboBoat: https://robonation.org/programs/roboboat/
PS: Depending on your panel (and your final battery chemistry options), I would recommend one of these:
Note it doesn’t work to recharge NiMH’s
Liam
hi,
Basically, it will roam around to gps locations, stop, take some sensor readings and or photo and move onto the next location after transmitting the data. The work the pi’s will be doing is fairly light weight. I have had it running on a battery pack that contains about 8 18650(or similar code) batteries in it for a couple of days.
Karen
Hi,
Just a follow up regarding the solar panel. It seems to get to a max of 25.5V in the sun. Walking through the house, it goes down to 17 so that is a bit weird but ok. This panel is a little weighty so if there are newer lighter options out there that can help, then I am open to suggestions.
Something I am also pondering is if it would be better to have the pico and motors, or just the motors running of one batteries and the other items running on a seperate battery. I wonder if this would help level out any power drain issues. And also mean that the Pi’s should be able to function if the motor battery goes flat (I should have thought about this sooner).
Those links look pretty cool.
Karen
Edit: Just another thought. The goBilda battery can’t be charged and discharged at the same time, but could you have 2 batteries that is can switch between? So one charges while the other is being used and then swap between as appropriate? Yes, I realise this could change the complexity a bit.
Hi Karen,
You might be able to simplify your robot by using a single Pi and Pico like Tim: Assemble a goBILDA Outlaw Chassis Kit - Plus Raspberry Pi and 8BitDo Control! - Tutorial Australia
Not weird at all! The voltage (and total power) changes depending on how much energy the panel receives,
Definitely a good idea, that’s done in a lot of robotics projects, the ‘tractive’ system will have a separate supply or contactor to cut power incase anything goes wrong.
It might be worth looking into some lithium based camping gear, charge controllers for those batteries often allow for solar and output to be running at the same time.
Keen to see what you come up with!
Liam
Hi,
Thanks for the info. With this idea…
When looking for a lithium battery, I am guessing 12V but what amp do I need as a minimum? Especially for the motors.
Karen
Hey @Karen107000,
You’re doing a great job planning ahead, battery sizing is definitely one of the more critical parts of your project.
For planning purposes it’s good to budget for worst-case usage:
- If your motors draw around 10 amps under load, and your Raspberry Pis and peripherals add another 2-3 amps, you’re looking at a total draw of about 12-14 amps while the system is running.
- Multiply that by the number of hours you want the system to run and you’ll get a rough idea of the battery capacity needed. For example:
- 2 hours of runtime → about 28Ah
- 4 hours of runtime → about 56Ah
It’s also important to consider that the rated capacity on a battery label isn’t always the usable capacity, especially with certain chemistries. For instance:
- Lead-acid batteries (including AGM or gel types) are typically only usable down to about 50% of their rated capacity if you want decent cycle life.
- LiFePO4 batteries generally allow more usable capacity (often 80–90%), so you get closer to what’s printed on the label.
Based on the estimates above, a battery in the 40–60Ah range should be a good fit for your project. Keep in mind that this is based on a worst-case scenario where all components are drawing their maximum current simultaneously. In practice, the actual current draw is likely to be lower, and with solar charging in the mix, you may see even longer runtimes.
Hi,
Thanks for that information, it is awesome.
One last question. I am looking at one battery that has for its output 12-16V 10A (Max) does that relate to the first bullet point so the 10A (Max) is the total draw that can come out of the battery?
This of for a battery pack, could two of them be joined in parallel (I think) to boost that to a max of 20A?
Karen
Hey @Karen107000,
No worries, really sounds like an interesting project!
Exactly right, that 10A (Max) rating refers to the maximum continuous current the battery’s output is designed to supply. If your motors and electronics try to draw more than that, the battery could shut down, overheat, or trigger a protection circuit depending on the pack design.
Yes, you can connect two identical battery packs in parallel (positive to positive, negative to negative) to effectively double both the available current (up to 20A max in your case) and the overall capacity (Ah). It’s important that the batteries are the same model, have the same voltage range, and are at a similar charge level before connecting them, this helps keep the system stable and safe.
Always check the manufacturer’s specifications and safety recommendations for the specific battery packs you’re using.
