Ideas? How to maximize robot play time?

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Ideas? How to maximize robot play time - NiMH Batteries

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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

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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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The big problem with any kind of Lithium battery, (or any other type of battery for that matter), is actually reading and following the spec and reference circuit for the device.

How to cause a fire or explosion using any battery chemistry :

  1. Over charge them or charge using excessive voltage/current.

  2. Overload them for extended periods of time.

  3. Don’t provide proper ventilation so the battery can dissipate heat generated while charging or in use.

  4. Place them in an environment where they get too hot. (i.e. Near a heat source or hot room/car.)

These cautions are valid for any battery type. So long as you read and follow the battery’s specs, you’ll be fine.

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