Ideas? How to maximize robot play time?

Esoteric Post -

Ideas? How to maximize robot play time - NiMH Batteries

I’ve got a couple of ideas:

  1. This might sound stupid but get a bigger battery. Most of the “soft” benefits can be exploited and yet they’ll only give you so much in return. By getting a bigger battery, you’re effectively multiplying the capacity by how much more you add.

  2. Use a Li-Po battery. Compared to NiMh, it has:

    • Higher energy density per mass. It has up to 30% more Wh/kg.

    • Smaller internal resistance - thus it loses less energy when it’s drained.

    • Double the number of cycles.

    • Lower discharge rate than the latter.

    • But it loses at the operating temperature: the NiMh can go under freezing temperatures, whereas the Li-Po can’t. It’s also a bit more painful charging up the battery, due to its quite complex procedures. You’d have to redesign your charging dock. And your best bet is in going with 3 cells because that gives you a nominal voltage of 11.1V.

  3. Using a Li-Po battery infused with graphene. They generally hold up their charge better than the regular Li-Pos and you can squeeze even more cycles out of it. They are a tad more expensive.

  4. Since the motors can’t be tuned, you’re only left with the Raspberry Pi. Maybe you try stopping all non-essential services from the Raspberry Pi and maybe even reduce the clock frequency or/and voltage of the CPU. I don’t expect to get much out of this, but it’s a lead. I think this one gives you the worst bang for the buck in terms of spent time.

Here’s a quick summary. Check out the table.
https://batteryuniversity.com/learn/archive/whats_the_best_battery

Thank you!

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Thanks @RobertLucian

Your response contained a real “gold nugget” for my bot that explains what I have been seeing and is immediately useful: (Battery University “What’s The Best Battery”)

High maintenance — battery requires regular full discharge to prevent crystalline formation.

And in the table it shows “Maintenance Requirement: 60-90 days”

I was thinking that full discharges should be avoided, but it turns out they are required periodically.

As to “We’re going to need a bigger boat”; My prior bot used 5000mAh NiMH C-cells, and I have contemplated trying to fit eight of them inside Carl which would double the playtime to a max of 10 hours.

As far as upgrading to Lithium technology, I am nearly paralyzed by my fear of a battery fire, as much as wanting to avoid the added complexity, and the difficulty of finding a compatible controller that supports “charge while running and allows disconnecting the charging source”.

I do have a desktop RPi that has a LiFePO4wered UPS which has enabled that RPi to run Boinc SETI continuously for two years, in spite of our local “Florida Flicker And Flash Power Company”. It is a great UPS for a desktop Pi, but too limited for GoPiGo3 configuration.

Thanks for taking the time to think about my question. Very valuable.

Alan

Hi @cyclicalobsessive,

As far as upgrading to Lithium technology, I am nearly paralyzed by my fear of a battery fire, as much as wanting to avoid the added complexity, and the difficulty of finding a compatible controller that supports “charge while running and allows disconnecting the charging source”.

Lithium technology is tricky, but I think as long as you are being cautious and follow all the safety procedures, you should be okay. I think the hard part is finding a charger that it’s suitable for your setup.

In the end, I think the best bet is in just getting a bigger battery. That’s going to give you the best bang for the buck.

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