Lithium Polymer (LiPo) Battery Upgrade Questions

[BillB]

I am looking to upgrade my Bioloid to a Lithium Polymer battery. The internet is full of warnings about the dangers of charging and discharging and there is a lot of information about implementing these batteries on RC Planes & Helicopters. But unfortunately there is very little information on implementing a Lithium Poly battery on humanoids robots.

So I would like to start a new thread to try and answer some common questions:

Q1:Do the humanoid robots (Bioloid, RN1 etc.) need a current or voltage regulator? What happens if they don’t have a regulator? Which regulators do you recommended?
Q2:Is a dedicated low voltage cutoff cuircuit required (to prevent over discharge)? Or is the voltage sensing circuitry of the RN1 and Bioloid sufficient?
Q3:What is the Maximum current draw of the Bioloid, RN1 etc?
Q4:What is the recommended cell configuration for each humanoid Robot model (is it 3S or 3S2P for Bioloids?)
Q5:Has anyone found any LiPo batteries that are the same size as the current NiMH pack in the Bioloid & RN1?
Q6:How should the LiPo batteries be protected – are foam dampers required, is ventilation required?
Q7: Are there any off the shelf LiPo upgrade kits upgrades available for the Bioloid (or for any other model).

Answers to any of these questions very welcome.

[Robo1]

Hi Bill

Q1: Yes, if you don't your likely burn out a the servo motors or H-Bridges. I use a normal regulator the sort that you get from maplins 5A should do the trick. I'm at the moment looking at traco power DC-DC converter, look at RS or Farnell.

Q2: The only thing I use is the standard LED warning light that you can get from the same place that you get the battery e.g. the LED comes on then the power gets low. You voltage sensing circuitry in the RN and Bioloid should be alright to do the job but as I don't have one I haven't tried.

Q3: I would say 5A would be pushing it. more like 2-3A.

Q4: depends on that you want. If you bot wants 6V then a two cell will do, But have a look at the lowest discharge value of the servo and the regulator. For example I regulate my KHR-2 with a 12V Reg and a 3 cell battery so, When the battery gets to below 12V I lose lots about 1V more power because of the 12V reg. I should really use a 4 cell but I found a 1000mha 3 cell that fits nicely in the chest. I could have made a circuit that when the Voltage drops below 12V it by passes the regulator but this turned out to be quit a big circuit so I drop the idea.

Q5: a 1000mha should be around the same size. measure and have a look on the web, most lipos are roughly the same size for the cell count and capacity.

Q6: Not really sure my battery sits nicely in side the main body really well so I just left it like that.

Q7: It's such an easy job it's not really worth it one inline reg and 2 capacitors and that's it.

See you in a couple of weeks Bren

[BillB]

So sounds like all I need is:
-> 3 Lipo Battery packs soldered together in series.
-> 1 Voltage Regulator.
-> LED for a low voltage warning light.
-> Specialised LiPo battery charger

Is it really this simple?

[Robo1]

Yes.

But don't solder together the lipo packs just buy a 3 cell lipo in the first place. You can get all the stuff from a RC shop. Just check the voltage before you plug it into the bot.

Bren

[limor]

Check out the sizes of the lipos and regulator sold at http://robosavvy.com/store/index.php/cPath/31
the dimensions of the 2000mah is for example 0.23x2.1x2.1" (5.8x54x54mm)

[BillB]

Wow it really does appear to be that easy. I had better start ordering in the parts then.

Neither Maplin nor RoboSavvy seem to have a 5A 9V regulator. Mapin have a 2A 9V one though. Is it possible to run 2x2A regulators in parallel? Or am I asking for trouble doing this?

[JonHylands]

Why do you want a 9v regulator? You can run the Bioloid bus off anything up to 14 volts, so three cells will run 11.1 volts nominal, or 12.6 max (assuming fully charged 4.2 volts per cell).

- Jon

[JonHylands]

Sorry, guess I missed your question in the first post. You do not need a voltage regulator to run a Bioloid kit (AX-12 based) off a 3S LiPoly battery. You can just plug it in directly.

The Bioloid is kind of unique in that regard, being a much higher voltage system than is typical.

Note that you absolutely should not plug in the power brick if you're running the system off a LiPoly battery pack. You can either run it off battery, or remove the battery and run it with the power brick.

- Jon

[BillB]

Thank you Jon. That saves me a bit of soldering.
All that is left to do is order the battery pack and decide upon a low voltage indicator.

For low voltage indicators this looks interesting:
http://customidea.com/shop/product_info ... cts_id=102

and this looks like a neat & inexpensive hack:
http://www.iroquois.free-online.co.uk/lithled.htm

[JonHylands]

Yeah, they look good. Personally, I will (given what I plan to invest in LiPoly) invest in a commercial low-voltage indicator. They cost less than a single LiPoly battery pack, and if you save even one it will be worthwhile.

- Jon