Tree Climbing Robot

Step 4 Power

The robot's power is supplied by two different sources.  The Arduino and the motor controller logic circuitry are powered by a 9V battery, while the motors are powered by an approximately 12V Li-Ion battery pack.  

I wanted to avoid having to buy an expensive LiPo/Li-Ion battery pack and charger, so I searched through my piles of electronic junk for a device with an appropriate battery.  I settled on the battery from a 12" iBook laptop.  The battery was 10.8V and 50Wh, but it was a little large and heavy for my needs.  To fix this, I tore it open and had a look at the internals.  I found that the battery was comprised of six 3.7 volt cells.  These cells were organized in pairs of two wired in paralleled.  The three pairs were then wired in a series, making a total 11.1V.  To shrink the pack but keep the voltage, I simply removed one cell from each pair.  The final battery pack had only half the capacity and half the discharge rate of the original (now only 2C), but the full voltage.  I then wrapped the cells together with electrical tape so they would hold their shape, and soldered a quick-disconnect connector to the battery leads.