Let's Make Robots!

Voltage Regulator?

The 3 volts from 2 AAA's that I was using for my small project isn't enough to make it speed across carpet due to the voltage loss across the components.  The motors end up getting about 2 volts instead of the full 3 they need to even move (I've tested it).  So, I wanted to just throw in another AAA and bump the whole thing up to 4.5V (I did the math ... all the components, including the LED's, would be fine).  Only problem is ... the robot (Blinky) is so small that there's no room for another AAA battery.

So anyway, I was at Radio Shack today and I picked up a 5V voltage regulator.  I'm not totally sure how it works, though.  Is it meant to take 5V, and then stabilize the voltage to stay there?  Or, can I hook it up to a 9V or 12V battery and power my project with 5V through the regulator?  Also, if I do that, will it overheat?

Lastly, what's the difference between using a voltage regulator and just doing the same thing with resistors? 

Notice the forum category ... sorry I'm a noob.  :) 

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common regulators, like the 7805, will take an input voltage of up to around 12-15 volts depending on the IC. If the input voltage is above 5-6 volts, the regulator will output 5v. If the voltage is less than that, the power is just passed through the regulator. So, with something like 4.5 volts, the regulator will just spit that through, and not  do much. Most of the time, voltage regulators don't need heatsinks. My robot's regulator is a tiny SMD device, which outputs 5.05 volts at 1 amp from 5 AA batteries. I don't have a heatsink for it, but if I wanted to use that full 1 amp of power, I would need a heatsink for sure. This regulator will continue to give me 5 volts as the batteries wear down, unlike using resistors which not only waste heat, but don't keep the voltage steady. ie, as the batteries run down, your motors are going to slow down as well if you're using resistors or not.
Great!  You answered all of my questions.  Thanks for the help!

Expanding on this a little, the recommended voltage for the 7805 is at least 7 volts to have reliable and stable voltage(depending on the model, ymmv). 5 AA(7.5v) cells or 6 rechargable 1.2(7.2) volt cells(see rc car batteries) should do the trick.

9 volt battiers aren't recommended as they usually are a low current rating, though they are ideally small. Best bank for the buck and small size would be using rechargeable AAA cells.

There  are regulators known as LDO regs which are low drop out, which, for example allows you to run 3.3v from 4-5.5 volts without the voltage wavering too much from the input voltage, but these usally are also low current.

 Then you have the buck/boost regulator that can give you 5.0 volts at 60ma via 1.8-5.5v power source(71055)...but these are getting into low current where you have to make sure your circuit won't draw more than what is available.

Anyway, these are just some examples and other info...you may not ever need the second two, but it's good to know that they are available should you ever get into very complex robot building where you have a small power source and need to take advantage of every single bit of charge the battery has to give(Think NASA Mars rovers.. )   :)

TYVM for the details. I thought thats what a regulator did, but wasn't sure.

Both the question and the answers are greatly appreciated =)