Page 378 - Hacking Roomba

Chapter 15 — RoombaCam: Adding Eyes to Roomba 359

So the first thing is to test how much power just the WRTSL54GS draws, since it likely
sucks the most power. Figure 15-18 shows the power consumption of the SL after it is booted
and a file is being transferred to it. At 358 mA it draws less power than the WL-HDD, which
has a CPU almost twice as slow. The SL is a newer design and doesn’t have an IDE interface,
which perhaps accounts for the difference. In any case, it’s a pleasant surprise. At 400 mA
current draw (being conservative) of just the SL, the 2700 mAh battery pack should last about
six hours.

FIGURE 15-18: Measuring current draw of just WRTSL54GS

Figure 15-19 shows the current draw with the peripheral pack added. The webcam is taking
pictures once per second and saving them to the flash drive. Doing that adds only about
another 100 mA to the power consumption. This is great. This means that with the battery
pack, the entire assembly can go for about five hours.
Alternatively, if you ran off the robot’s 3000 mAh battery pack and don’t run the vacuum
motors, Roomba will draw about 500 mA, the SL and peripherals will draw another 500 mA,
and you’ll get a couple of hours of run time.