Batteries

Power requirements for this robot are going to be slightly more than a few AA's in a battery holder. The chassis can carry unto 2 sub C packs with are often found in RC cars. The Arduino requires an input between 7v and 12v as it has its own voltage regulation to 5v and 3.3v and the motors in the chassis required around 6v - 7v, so I decided on a 7.2v pack. The VNH5019 can power the Arduino however it features no regulation so the voltage input to it must be suitable for both the motors and Arduino, which 7.2v is.

I naively plunged straight in and ordered some Lipo (Lithium Polymer) batteries as most robot websites seemed to stock them in their various forms. I picked out a 7.2v Sub C sized pack, and Lipo charger. However after placing the order I decided to look into the types of batteries a little more and found to my horror Lipo maybe wasn't the best choice. It seems they require a lot of care and attention with regards charging and discharging. Batteries had to be kept balanced and couldn't be fully discharged.

After looking at various forums it became clear this was something that really should be used outside the home in a garage or workshop rather than a spare bedroom due to "abused batteries" potentially catching fire. Lots of sites recommended charging in flameproof bags or buckets of sand. Now a lot of this info was written when Lipo's first came out and I know things have probably moved on since then, but I really didn't want to risk it.

NiMh an older battery technology again used frequently in the RC arena looked like the better option. The major differences between NiMh and Lipo appeared to be capacity and weight. Lipo is lighter and the density is greater giving a larger Mah (milliamp hour) for the equivalent weight, however NiMh is a little more forgiving with the charging and discharging, and while caution should still be taken while charging (never left unattended) a bucket of sand wasn't a recommendation :).

Battery capacity wise I wasn't sure where to start and what I would need. The motors I was using had a no load current of 420mA X 4 ( approx 1700mA ) and approximating normal running with the chassis maybe double that. The Arduino and a few sensors I didn't think would be mush more than 3-400mA.

• Motors approx 3000mA - 3500mA
• Arduino approx 400mA
• Total around 4000mA.

I therefore chose a 4300mAH battery to hopefully give me an hour or so between charges.

Now to fire it all up and see how it runs :)