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Pi Robot
09-12-2010, 10:23 AM
I may have some funds to upgrade the base on my robot with the hopes of having it roam for several hours at a time while collecting vision data. I am toying with the idea of a Videre Era Mobi base but I think all I really need are bigger motors and battery for the base I already have.

I am currently using a 3A version of one of these:

http://www.batterygeek.net/200Wh-Portable-Power-Station-SPPS200-3V-28V-p/spps200_batterygeek.htm

for logic power (including an onboard Zotac motherboard), and two 8.4V NiMH 4000mA battery packs for drive power.

I'd like to use just a single Lithium ion battery but with at least 6-10A peak current and at least 10000mA run time. I would get two of them and keep one recharging while the other was in use. The model above comes close but I don't really need all the voltage selections--just something like 24V max and then a distribution bus with other voltages for the various components.

Which brings me to my second question: what would you recommend as a distribution bus, with say 5 V, 12V and 19V terminals? (I'm hoping for something pre-made for this purpose rather than having to build one from scratch.).

Thanks!
patrick

lnxfergy
09-12-2010, 11:39 AM
I don't have any answers -- but I look forward to what might come out of this thread. My large PC-bot REX was using a 12V 17Ah SLA battery (at a whopping 12lbs). I'm currently using this battery in the next revision of the bot, but starting to get close to 25lbs overall and so shaving some weight off the battery would be nice.

I have noticed in the PR2 manual, that they use an array of this battery: http://www.oceanserver-store.com/18.html



The battery system has four battery bays. Each bay is comprised of four
Ocean Server BA95HC-FL 14.4V Li-ion batteries, a V-INFINITY VF-S320-
18A-CF 18V AC-DC Power Supply, and a Ocean Server XP-04SRW four-
channel high current battery controller. This provides the PR2 with approx-
imately two hours of countinous operation after a full recharge. For more
information, see the ocean server package at ros.org.
-Fergs

Pi Robot
09-12-2010, 07:02 PM
Thanks Fergs--this is the kind of thing I was looking for. Just a flat battery with good capacity, light weight and not a lot of bells and whistles I wouldn't use (but probably add to the price).

--patrick

Pi Robot
09-18-2010, 08:09 AM
In researching battery packs, I was looking at the voltage requirements of various components. In the AX-12+ manual, the specs call for 7-10V (recommended 9.6V). In the ArbotiX manual, the recommended voltage for the dynamixel bus is listed as 11.1V. And the output on the CM-5 AC adapter is 12V but I don't know if it is down regulated inside the CM-5. In any event, does anyone know the true upper voltage that is safe to use with the AX-12s? For example, the Ocean Server battery pointed to above is 14.4 V but they also sell DC-DC converters that will bring this down to 12V. There is also a newer battery type called LiFEPO4 that is apparently much safer than "regular" Lithium-ion batteries and a typical high capacity pack is rated at 12.8V. See for example:

http://www.batteryspace.com/Polymer-LiFePO4-Battery-Pack-12.8V-10Ah-128Wh-30A-rate-with-PCB.aspx

In all these cases, the battery voltage will be highest immediately after a recharge. For example, the pack above has a max voltage of 14.6V. So I am guessing that a DC-DC converter is essential, but the question is, is 12V too high for the dynamixels?

Any thoughts?

--patrick

Pi Robot
09-19-2010, 09:47 AM
I'm almost ready to buy the following battery:

http://www.all-battery.com/tenergy9-6v16ahlifepo4batterypack.aspx

together with the following DC-DC converter:

http://www.batteryspace.com/dc-dcregulatormoduleinput6-24voutput3-5-12v160wwithconnectorscable.aspx

I'm assuming I can run the dynamixels at 12V off the converter or directly off the 9.6V battery.

Can anyone see a problem with this setup?

Thanks!
patrick

lnxfergy
09-19-2010, 10:05 AM
I've run AX-12s off the following:


7.2V NiMH. Servos are lethargic as possible. Realistically, 10-12V is a good operating range.
11.1V Lipo with no issues. Max voltage on a fresh charge is ~12.6V. (Note that the new Bioloid Premium actually ships with an 11.1V lipo).
12V SLA with no issues. Max voltage on a fresh charge is around 13.8V, but quickly drops to around 12.6v.
12V NiMH. The max voltage fresh off the charger is typically around, or slightly over 14V. The servos report "Voltage Error" for some time, until the voltage gets low enough, but continue working all along.

TYPICAL DISCLAIMER: I'm not making any recommendation off this, use voltages >12V at your own risk. This is my personal experience, YMMV

-Fergs

Pi Robot
09-19-2010, 10:26 AM
Thanks Fergs.

--patrick

billyzelsnack
09-19-2010, 03:36 PM
Unless you have a safety concern.. Lipos all the way..
http://hobbycity.com/hobbyking/store/lithium_polymer_battery_configuration.asp?cap=4&con=3&x=70&y=11
I'd much rather have multiple packs in parallel vs one giant pack anyway. If a cell goes bad in a huge pack, you're outta luck unless you're nuts and are willing to do lipo surgery.

(They have LiFePo4 too)
http://hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=10310

Another LiFePo4 option is to build your own from a DC9360 Dewalt pack.
http://shop.ebay.com/?_from=R40&_trksid=p3907.m570.l1313&_nkw=dc9360&_sacat=See-All-Categories

DresnerRobotics
09-19-2010, 05:59 PM
One thing that I will chime in on: not all lipo packs are made equal. When I first went to lipos I picked up the cheapest I could find for the cell/capacity I was looking for (tenergy brand). Within a couple of months of light-moderate use, I found they started to slip in capacity, finally to the point where 1 or 2 of the cells would rapidly lose charge within a few minutes of use, rendering the entire pack unusable. 9 months after I bought these batteries, I had $200 in paperweights.

I have since switched over to ThunderPowet brand, which is pretty much some of the best in the industry, and have been going over a year with hiber use, without even the slightest sign that they're losing capacity.

I'm speaking from personal experience here, not trying to be a salesman, but there is a reason our store only carries thunderpower, and it's a result of my own experience with lipos. They're kinda like servos, you get what you pay for.

billyzelsnack
09-19-2010, 07:07 PM
I always get in this lipo argument with ya Tybs. I totally disagree, just like the last 4 times! haha.

The RC community is pretty happy with cheap lipos ( you just need to do a little research ) and RC abuses them 10 times worse than robotics currently does. http://www.rcgroups.com/forums/poll.php?do=showresults&pollid=4050

I guess I should also point out.. My opinion is probably biased by the fact that it does not really matter what battery brand you have when your RC helicopter crashes into the ground at 50mph. At that point you'll be wishing you opted for the cheaper pack. Especially if you don't have a lot of flights on your new pack! This whole crashing problem really is not a problem with most robotics applications.

DresnerRobotics
09-19-2010, 08:48 PM
I guess I should clarify that Ive only dealt with two cheap brands previous to my thunderpower switch, but I've never been happier with the switch. I also like the option of using the milspec line, which is insanely light/compact. Definitely can't compare genetics there, but they're spendy.

I'm all for disagreement Billy! :p At least you cite your sources.

Pi Robot
09-19-2010, 10:00 PM
Thanks for the suggestions. Safety *is* one of my top priorities since every time I recharge my current lipos I wonder if this is the time I burn the house down...The LiFePO were new to me and it sounds like they are much safer than lipos. Also, in terms of capacity, I am looking for something at least 10000mAh in a single battery so I can run the robot for several hours on a charge and I only have to charge one battery, use one DC-DC converter, etc. Seems that Hobby City tops out at around 4500mA per battery. The ThunderPower site lists lipos up to 8000 mA but not LiFePO as far as I can see.

--patrick

billyzelsnack
09-20-2010, 01:06 PM
Well if weight is not a super concern, then A123 packs it is! With a Dewalt pack and two more cells you could make a 3S4P pack that is 9.9V nominal and 10400mAh for 840g in cells.

btw. You can parallel charge your lipo packs.
http://www.rcgroups.com/forums/showthread.php?t=932319