# How can I design a light-weight, on-board battery & charging system for a self-charging robot?

My project involves the robot navigating to its charging station, docking, charging, then resuming whatever it was doing. The robot is a hexapod with 18 leg motors, 2 camera motors, and will be operating on an NVidia Jetson Nano (which shouldn't use more than 5W according to the website).

Since there are so many motors, I'm planning on a 5-6S li-po or li-ion. I expect the system to use around 10-30W while operating. I want to keep it compact, but at the same time I don't want to have to manually plug the robot into a balance charger. The charging station design I have in my head consists of 2 metal contacts on either side, which connects to some charging circuit. The charging circuit needs to be able to charge the batteries without powering off the robot.

I've done quite a bit of research to the best of my ability into products that might solve this problem, but I'm afraid I either haven't found anything or haven't been able to understand anything...

I don't want to have to design / fabricate the circuit if I have to, since the bot catching on fire would be many \$, but I am capable and willing.

Do such charging modules exist? How do engineers in the autonomous robotics industry solve this issue?

• engineers build their own charging station and circuits. that is how they solve the issue. I have never seen such generic modules for sale. But there are charging ICs Apr 11, 2020 at 19:36
• If your robot catches fire unattended you have bigger problems than a lost robot. consider LiFe. a bit safer Apr 11, 2020 at 19:42

## 1 Answer

My father used to repair the Swisslog Transcar system at a local hospital, and I've helped him a couple of times. They solved the problem exactly how you described. The robot parked itself over a charging station, the central control computer sent a signal to the charger to elevate the 2 metal contacts under the car, and the charger was turned on. When the charging was done, it turned off, and the robot went on to do its job. They used two car batteries (maybe truck, I don't remember), so 2x12V or 2x24V lead acid types (it's an older system). I think the charger circuit checked the current and battery voltage.

I don't know any finished module for this application (only for 1 cell Li-ion), but Li-ion batteries aren't very difficult to charge either. Use constant current source for your series of cells, and use a shunt per cell that doesn't allow your cell to go over a certain voltage. (My father built something like that from a handful of old parts, like LM317 and TL431 and resistors, not exactly rocket science, but you can build a more sophisticated one) For safety you could use a thermometer to detect any anomaly early and shut it down. Also to protect the battery and prevent your robot to get stuck somewhere, check the voltage regularly from software (dropping under a certain charge hurts it)!