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sniperscope
05-13-2009, 03:16 PM
Hello Everyone:
I'm in the process of adding additional servos to my Bioloid. 2 additional for the arms. 1 for the waist and maybe 1 or 2 to get have tilt/pan for the head. 23 total. My main concern is weight. Could I sub the batteries for the lighter Lithium rechargeable ones? If not, are there any alternative power sources I could use? At the moment a nuclear reactor is a little too big lol.
Thanks

Sigma X
05-14-2009, 04:34 PM
that seems ok to do and actually projects are already done using LiPo batteries
but to be safe check out http://robosavvy.com/site/index.php?option=com_openwiki&Itemid=&id=robotis_bioloid this should have the info you need if not i'll gather the info for you

lnxfergy
05-14-2009, 05:37 PM
The stock bioloid humanoid has something like a 500g payload capacity (determined via empirical testing by one of the members on this board). AX-12s are ~ 55g each, so three is only 150g. I don't think you'll have any issues with carrying the 3 extra servos and related brackets -- but you will have shorter battery life. The primary reason to upgrade the batteries is to get longer battery life....

-Fergs

Sigma X
05-14-2009, 06:54 PM
and there you have it info from an expert rather than some junk collector

tom_chang79
05-27-2009, 09:35 AM
LiPo is probably the best way to go to shave off some pounds. It's not just for longevity. If you compare just capacity (mAH) between LiPo and NiMH, the same capacity LiPo weighs half as much as a NiMH technology (which is what the Bioloid defaultly uses).

One quirk of LiPo is, don't forget to get the appropriate LiPo cut-off circuit with the LiPo pack, as well as a balancer (you will use multi-cell LiPo to achieve the 9.6V required for Bioloid). LiPo has a quirk in which if you discharge it below a certain amount, it puffs up. Also, if you damage it, it will swell up again and sometimes cause small fires.

From a safety standpoint, you're better off with the NiMH technology or A123 (LiFe technology) chemistry. If you do want to get LiPo, make sure to get hard-cased ones...

One thing I never figured out: Each cell (S) of a LiPo is roughly 3.7V. A 2S pack will get you 7.4V, a 3S pack will get you 11.1V. Not sure if you want to do a 3S with a big regulator on-board. What do you guys out there with LiPo-powered Bioloids use?

Adrenalynn
05-27-2009, 09:45 AM
The AX-12's will run just fine at 11.1v. I've no idea bout the CM5, don't have one, but for sure the AX-12's like 11.1v.

tom_chang79
05-27-2009, 09:50 AM
Thanks for such a quick response! Servos always love more power! It's always been a matter of not going over the breakdown voltage of the FETs and not going over the junction temperature of the device...

I remember when I first go into this hobby about 4 years ago, I powered up my HS-645MGs with my 6-cell NiMH matched Sub-C packs I use in RC racing. The servos heated up in no time, but when it was powered, it was like crack for the servos!

:P

Adrenalynn
05-27-2009, 10:34 AM
In this case, it's more about not burning-up the windings, but [shrug]

As I noted - the servos will handle the 11.1v with no more heating than at 7.4v. Typically less since you observe lower current draw at the same load, and the servos typically will be running at less than their max torque.

Some of the most robotis-savvy here run them at 12v, in fact...

ScuD
05-27-2009, 11:45 AM
Typically less since you observe lower current draw at the same load, and the servos typically will be running at less than their max torque.



This is why I got confused the other day with undervolting motors and their current draw.

Anyhow, I just remembered having an 11.1v lipo pack laying around from a helicopter I bought a year ago.

Might give that a try..