Servo - May 2009

MicroNightmare about to deliver a Really Bad Daydream to an unidentified victim. Photo by Seth Carr.

Fighting in the well travelled SozBots arena, Jamison Go took first with Lil Ron, with owner

Winner Jamison with his prize — a Spektrum 2.4 GHz system — presented by Jim Smentowski. Photo by Seth Carr.

Jim in second with Shazbot. A crowd favorite was his antweight version of BattleBots behemoth

Sozbots arena, after wandering 3,000 miles east, has found a new home in Florida.

Nightmare, although losing both motors and wheels limited its motion a bit. SV

CHEAP P WER

● by John Frizell

Power packs can be expensive, but if you build your robot from cordless drills you have two battery packs complete with chargers left over. Use them to power your bot.

Free batteries with chargers are not to be sniffed at. The nicads that come in cordless drill power packs (Photo 1) are not of the highest quality, but they will get you going and power your robot for a year or two of battles. You will want to replace them at some point because the high discharge rates of robot combat will weaken them and their power density (amount of power you get from a given weight) is poor compared to batteries designed for this purpose. The less

weight you use for batteries, the more you can put into armor, drive, or weapons.

The usual chargers that come with low cost cordless drills are slow — they will take five hours to recharge a battery. Still, your two batteries should get you through a day of fights with one in the machine and one on charge.

PHOTO 1. The batteries inside a cordless drill battery pack.

Another approach — provided that your speed controllers can handle the voltage — is to put the two in series. Most cordless drill motors will easily handle double voltage for a three to five minute fight. They will run twice as fast and — because power goes up as the square of the voltage ratio — your bot will hammer four times harder than it would with a single battery. It will also run down your batteries four times as fast. To recharge them, just take them out of your machine and plug them into their chargers.