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Asimovian
11-27-2008, 11:49 PM
Hi everyone,

First off I just wanted to say that there is so much useful info on this forum! Just from reading posts over the last couple of days I can see there are some really intelligent people on here and some great indepth discussion.

My question is regarding the choice of batteries to use in a pc based robot. I am using the following major components: VIA pico ITX, SSC32 servo controller, sabretooth 2X5 motor controller.

For most of the PC based bots on here I've seen a majority of people use sealed lead acid batteries but I am more interested in lithium polymer batteries for the smaller footprint and lighter weight. I've previously had a bit of experience with RC cars and have always used a small voltage regulator for the receiver. Am I going to need any of these for this type of application? I know the sabretooth already has protection onboard but I can't find any definitive answer about the ssc32 and what effect it would have on the pico board.

Sorry if this question is a bit obvious or has been asked before, I'm just getting into the whole robotics scene and have so much information to absorb.

Can anyone offer any advice or experience with using lipo batteries?

Thanks,
Kirk

wireframewolf
11-28-2008, 12:12 AM
I can't help you with LiPo cause I've never used them, but...

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=2139

That's what I use to run my pico-ITX/servos/motors (also using the sabretooth). Just be careful with the pico's power supply. One power supply takes a range of voltage, while the other takes exactly 12v regulated. Even though it's a 12v battery, it's closer to 15v fully charged. So your choices are to get the proper power supply, or regulate the battery going in. I chose poorly and blew my first power supply : /

Nammo
11-28-2008, 12:34 AM
I built a small Mini-ITX based robot that used a LiPo. (Pic here: http://www.camppeavy.com/sitebuilder/images/nathan-378x275.jpg )

I used a 70 watt-hour Tenergy 3S-6350-T to power the mainboard. You can find it for around $80 most places. I got mine direct from Tenergy:
http://www.all-battery.com/111volt-6350mahheavydutyli-polypackwithpcb.aspx

One advantage of this type of battery pack is that it has an integrated PCB that prevents over and undercharging. Also, if you try to draw more than 75 watts it will trip, to prevent you from accidentally shorting the battery and causing an explosion.

A full charge takes about 3 hours with the Graupner GR6437 charger, listed first on this page: http://www.hobby-lobby.com/chargers_lipoly.htm

There are faster chargers out there but they cost more.

To power the 5V parts of my robot, I use an inexpensive Battery Elimination Circuit connected to my LiPo:
http://www.castlecreations.com/products/cc_bec.html

These are nice because you can get 5-7A of extremely clean 5V output. I eventually replaced my ITX motherboard with the more power-friendly BeagleBoard, and the same BEC powers the BB too!

I know some Pico ITX boards come with their own power boards. If you've got one of those, you can probably connect it direct to your LiPo. If not, there are some other options.

Here's what I used to interface the battery to my Mini-ITX board:
http://www.mini-box.com/picoPSU-90

I also found this forum very friendly and helpful:
http://www.mp3car.com/vbulletin/power-supplies/

They deal with interfacing ITX motherboards into cars, but a lot of what they have to say applies to robots too.

Some of these DC-DC power supplies, including the PicoPSU-90, wire the input voltage direct to the 12V rail. With a LiPo, that means your motherboard will see voltages from 12.6V-10.8V on its 12V rail.

This is actually okay for most motherboards, but if you have concerns you can use a pricier converter like the M2-ATX-HV. This guarantees that the 12V rail gets 12V no matter what your input voltage. One disadvantage is that you waste power and heat in the conversion.

- Nathan

4mem8
11-28-2008, 01:05 AM
Cool sites Nammo, I use these a lot, And a good choice for Asimovian to puruse at.

Adrenalynn
11-28-2008, 01:43 AM
Firstly - welcome to the forum!

I didn't see your SSC32 question answered directly, so I thought I'd chime in - if this is an echo - well - I didn't go through all the great info (+rep for both!)

The SSC32 has an onboard voltage regulator for logic, and can carry a couple SMALL servos on that regulator (250mA total including logic and devices). The Castle Creations power supply is a good choice for servos - 4mem and I use it too. Get the programmer if you can budget it so you can bump your voltage up to 6v for most hobby servos, or 7.4v for higher-end robotics servos.

You can power the logic of the SSC32 off of its internal regulator, and the servos from external power. Alas, it's a pretty narrow regulator on the input side - the docs call for input from 6v-9v. I've run it from 9.6v NiMH without any warming up.

You might want to wait for the RoboticsConnection ServoWizard if you haven't already purchased the SSC32. You can hook it up to a Serializer and get a multitude of control options and sensor inputs, all driven over the same control line.

No0bert
11-28-2008, 06:52 AM
There is an excellent battery calculator here:

http://www.societyofrobots.com/battery_calculator.shtml