Pololu 3pi Robot

You will only need a battery charger if you plan on powering your 3pi with rechargeable cells. You want a charger that can work with 4 NiMH cells in series (they are usually in battery packs, not in battery holders like on the 3pi) and can be powered by AC (a wall outlet). In general, having more flexibility (such as the ability to charge 1-8 cells) is nice for future projects. We regularly use the iMAX-B6AC balance charger/discharger for charging batteries here at Pololu.

Chargers like the iMAX-B6AC can be connected to the 3pi’s battery charge port, allowing you to charge the batteries while they are still in the robot.

Since the 3pi just uses ordinary AAA batteries, you can also use AAA chargers (into which you stick the individual cells) available at most general electronics stores. For example, a quick Google search yields:

4 AA & 4 AAA Ni-MH Battery Charger

(Note that we have no experience with this particular charger and are not specifically endorsing it.) The downside to a charger like this is that you have to remove the batteries from the 3pi to charge them.

Yes. The easiest way to augment your 3pi is through an expansion kit, which can comes either with cutouts that let you see the LCD below or without cutouts. The version without cutouts replaces the LCD, giving you access to more I/O lines and more prototyping space. An expansion kit is not required for addition of your own electronics, however.

The 3pi robot has a limited number of free I/O lines that can be used as inputs for additional sensors or to control additional electronics such as LEDs or servos. Please see section 10.c of the 3pi user’s guide for more information.

Because the 5 V goes through two power stages, the answer is not completely clear-cut. The 5 V regulator itself has a 900 mW power dissipation limit, so with a 4.3 V drop from the 9.3 V boost voltage to 5 V, we get just over 200 mA. The stock electronics on the 3pi typically use under 50 mA (however, this depends on what your program is doing, if you are making high-frequency noise with the buzzer, and so on), so you could figure an absolute max of 150 mA, with 100 mA being a more comfortable guideline.

However, the boost voltage has a limit of its own of around 1 A, which is dependent on your battery voltage. The motors and IR LEDs also use this supply, so using a lot for your 5 V will affect what is available for the motors. You can almost stall the motors and still have the full boost voltage on the motors in the stock configuration; if you’re also drawing an extra 200 mA for other electronics, the boost voltage will start dropping as the motors approach stall, though this is not necessarily a bad thing since it will limit the stress on the motors and lower the voltage drop on the linear regulator.