NiCAD are often 800mah where as NiMH are much higher current capacity 2600mah is not uncommon.

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Hmm, well I don't know if you know this store, it is called Giant Tiger. Just some cheap stuff here, and most of the times it is not all that bad. The batteries that I saw had "For Solar Powered Lamps" thing on them.

Since I am not going to be a using a voltage regulator and expecting the stuff to run on the 4.8-5V batteries, do you think I will be spending more time recharging then actually testing the robot? Because if it drains too quickly, the batteries might go into the unusable output voltage range and so I'd have to discharge and recharge.

So right now, is this my best solution... running the things off four NiCd batteries?

 

I think that four cheap NiCds is probably your best solution. The NiCds will stay near 4.8V until they are almost depleted.

As for spending time recharging, I suggest two sets.

You mention discharging as if it were a part of recharging.... I maintain that discharging is a colossal waste of time and effort. A "memory effect" is really uncommon in normal use. I have a lot of NiCds in use, for a long time, and have never experienced it.

 

In 'normal' use yes memory is rare. I think Nasa had a big problem with it because the charge cycle occured at exactly the same point in a batteries discharge state and it eventually developed a voltage dip at that point. NiMH's and Nicads alike will have a similiar problem with a generic charging circuit in things like cheap cordless phones. Because a lot of the time they're only used for a very brief period of time and then thrown on a charger again, these chargers are seldome fit to know the cell was only depleted only a fraction of a percent of it's charge and they tend to constantly trickle charge the batteries, which is just as bad.

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Souper man

O GOD!

Cadmium is seriously bad for environment, although its already pretty messed up.

Good example is lake erie in the 1970s lol!

 

Well I don't like NiCAD, I use NiMH when I can find them.

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The best deal I've seen for NiCad batteries is from Maplin
A real NiCd D cell 5500mAh for just £2.98!
http://www.maplin.co.uk/module.aspx?...=32624&doy=7m5

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Nicads aren't as energy dense or light as NiMh's but they're much more robust. Some RC fanatics still use them because they source current better. That's a very good price, especially for a D cell, I'd snap some of them up. Great for high current portable supplies.

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If you can afford the size and weight of NiCd, then consider gel-cell (Sealed Lead Acid). 20% larger, 30% heavier, less than half the price.

D-sized 5500 mAH, £2.99 x 5 = £15, 4.8 oz x 5 = 1.5 lbs.
6V 4.5 AH Gel cell, £5.99, 0.9 kg.

 

Wow I'm supprised no one has mentioned Li-Poly batteries yet, why is that? Are they not as good for robots? (Well besides the fire hazards and stuff) Because I use these for micro airplanes and such and they seem like they would be ideal for small lighter weight robots.

 

Li-Po's cost too much for hobbyist robotic enthusiasts (mostly). Also they need constant monitoring of the cells so that it wont blow up destroying the whole robot. Robots tend to be a lot more expensive than RC equipment (depending on the robot of course). And the miniature weight of the cells is normally not needed. If they are, then the robot is poorly designed and the mechanics should be redesigned.

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Check out FMA Direct. They are a bit expensive, compared to regular NiMh's or NiCads, but weight aside the physical size is an advantage. They also sell discharge controllers which sense cell voltage and activate cut off circuitry before the pack can be damaged. The packs and the chargers are designed to work together and the seperate charge cable from the discharge cable feeds into temperature/voltage sensative voltage elements which automatically ballance the packs.

www.fmadirect.com

If you need, or want the highest possible amount of energy storage in the smallest amount of space and weight lipoly's are the way to go. As bloody-orc stated though they're pretty pointless for your run of the mill line follower or bounce off the walls and wander around robot.

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