MOAR POW3RZ!!!

Obviously a roving robot is going to be somewhat constrained if it has to be tethered to its power source. So I began looking at some options for battery power.

The Robie chassis has a battery door which accepts 4 D-cells. So that's an obvious first choice. And indeed that's a valid choice. Although the Pi and most of the peripherals run on 5v and 4x 1.5v D cells = 6v, it's possible to use a buck converter to get 5v. But that means running out and buying pricey D cells every time I'm out of juice. And from what I hear Pi's can go through batteries quite quickly.

So my other option was to use some sort of rechargeable source. There are many types of rechargeable batteries. And indeed I could have used D-cell ni-cads if I wanted to. But nothing beats LiPo / LiOn for bang-for-the-buck. That's what's in your power hungry cell phone and your laptop.

LiPo cells can have tricky charging requirements. Charge them too much or let them drain too much and you can damage the cells - or worse - set fire to your house :( I thought I'd do away with these concerns by buying something prepackaged that already had a proper charging circuit embedded.

So this is what I ended up with. It's a USB power bank. It's intended for charging up your cell phone or your ipad on the go. But lucky me the Raspberry Pi also runs off of the exact same 5v USB source. This one is especially nice because it supplies 2 amps on one port and 1 amp on the other. So if I find myself starved for power I can split off the drain across the 2 ports. The stated capacity is 50000 Mah. That rating is pretty laughable. It's probably closer to 10000 Mah. But even at that it should provide plenty of roving juice.

Of course the power bank wouldn't fit inside the chassis without a few modifications (which is why you see the 18650 cells and the charging board separated from the case in that photo). Additionally I ran in to an issue where the board cuts power to the USB ports. So the "on" button needs to be accessible.

My solution was to put the charging board in the battery compartment so that one simply needs to open the door and plug the micro USB cable in to charge her up. If the USB power cuts out, just open the door and press the button. Simple. Elegant.

Unfortunately somewhere in the process I seem to have nuked the charging board. Sigh. So I've gone ahead and ordered a new one on Ebay. For anyone facing a similar problem, the thing to search for is called a "LiPo Boost Plate".

The life of a hacker is never dull...