Challenge Of Powering Robot 24/7

For more than 20 years I have wanted my robots to become independent - managing their own charging to allow 24/7 operation.

This year, with my GoPiGo3 robot, I substantially achieved this goal, and have learned more about the challenges facing a 24/7 robot. Specifically, in my case, the capacity of NiMH AA cells begins to diminish quickly around 140 to 150 cycles, 1200 to 1500 hours, or 2 months of 24/7 operation.


Batteries: Powerowl 2800mAH NiMH AA-cells

Charger: Tenergy 1025 Smart Charger set at 1A max rate

Typical Docked, Charge Time: 3 hrs

Playtime: Start at transition to trickle charging, end at 8.1v reported
(8.1+0.6 protection diode drop = 8.7 / 8 cells = 1.0875v/cell )

Load: Measured initial battery load of 318 mA at 9.6v


  • Raspberry Pi 3B ave load 0.00 (uptime),
  • GoPiGo3,
  • TOF-DistanceSensor,
  • USB powered speaker

Data Span: First 2 months 7-1-2019 to 9-6-2019

Life Point: After 156 docking cycles 1272 hrs operation in Carl


  • Minor capacity decrease until 145th cycle (10% or 0.07% per cycle)
  • Steep reduction in capacity in next 10 cycles (10% or 1% per cycle)


  • For Comparison: (candlepowerforums 2014 Eneloop at 500mA rate)
    100 cycles: near flat capacity,
    150 cycles: down to 90% capacity
    175 cycles: “Knee to 0%” at 80% capacity

Several people have suggested Lithium Ion as a better power source, but the charging complexity of these cells is quite a hurdle to integrate into my two electrical contact docking system, and most of the Raspberry Pi oriented LiPO hats have GPIO header pin conflicts with the GoPiGo3.

I just noticed a possible non-conflicting hat called the [u]PiJuice[/u], which could work for powering the Pi (5v) but getting the 7.2v - 12v to drive the GoPiGo3 board, and the extra stack height, and isolation, and who knows what else, will remain challenging.

Designing real world solutions is so complicated…

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Basically you are up against the size and load carrying capacity of the GoPiGo3 chassis which I suspect was not meant to carry much in the way of extra hardware other than light weight sensors and servos.

I have looked at these robot chassis and plan to use the GoPiGo3 to develop the necessary software to run the bigger chassis which can carry bigger loads and batteries. Like the GoPiGo3 chassis the Max '97 uses gear drive motors and it might be possible to attach an encoder to the output shaft on the back of the drive motor.

I have attached several pictures of the Max '97 chassis.



Tom C

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