Batteries for test platform

[robaxman]

I am building a test platform for experimenting with control systems for autonomous robots. I would like people's opinions on batteries that may or may not be appropriate, as I am very new at building platforms that weren't complete kits when I bought them.

I am currently planning on using a Zagros Robotics Max 96 mobile platform (I have two from a previous project).

http://www.zagrosrobotics.com/

The platform is 16x16, with one, two, or three levels, depending on what I decide to do with it at any particular time. I will also look at the new Trossen Robotics platforms when they come out later this year for a version 2. The drive system is currently 2 12V motors which draw 1.3amps each. I may eventually do 2-4 motors, maybe drawing up to 2 amps each. So I'm thinking drive systems that may be from about 3 amps up to 8 amps for the motors.

This is not supposed to be a battlebot, it won't need to move very fast, certainly not for long periods of time. I may want it to move up a medium steep hill by where I live, but otherwise, the drive system is not meant to handle really high loads.

Want I want to be able to do is play with different sensors and homebrew circuits on larger breadboards that are available on most hobby robot kits. I may sometimes use a laptop on board to provide the brains of the robot, though I also plan to experiment with GumStix, a nano-ITX, etc, at various times.

Version 1 of the platform will probably use a Scorpion XL motor controller.

What kind of batteries are appropriate for fairly long run times between battery charges, like 4 hours, given the loads the drive system is likely to be under? I have no estimates on weight, maybe 20-30 pounds, depending onif I am using a laptop, what other electronics are there, etc.

What I would like to use is Lithium Polymer batteries. They are very light, seem like good power densities, and are better for the environment when it inevitably comes time to dispose of them. Next in line would be NIMH batteries, little heavier, but still reasonable power density and better for the environment. I'd rather not use Nicads, but they strike me as better than Lead Acid. Sealed Lead Acid seem like they would be good for sustained high current situations, but I don't think I'd have those conditions often, they are heavy, and I'd like to avoid using lead.

What are the advantages and/or disadvantages of my favorites, and what should I consider that might drive me to choosing my least favorites? I have spent the day looking on the web, but most of what I found seemed more geared towards battlebots.

Thanks!

[Kevin Berry]

the key variable is run time. You spec'd everything else out well. Assuming one hour of run, you want 3 to 8 amp hours of capacity.

That puts you in "interesting" territory. If weight was a key constraint, go with LiPoly. But cost and some hazard in charging will be an issue.

NiMH are my favorite for this application, but you are looking to still spend a bit of money. Probably $60 or 70 for 3.6 amp hours.

Cheapest and maybe best for your app would be NiCads. I actually use the packs from Harbor Freight drills for testing my bots, then go to higher performance packs for combat.

Actually if this was my bot I'd buy an 8 AH SLA, which is rugged, cheap, and would run you very well.

For the worlds best battery advice I'd contact Steve Hill at www.battlepack.com and chat it over with him, he's a true expert and very helpful.

[wrighthobbies]

You pretty much have it down. Li-Poly/Li-Ion provide the best power to weight ratio, but highest cost. NiMH provides a good balance between power/weight and cost, but can't put out massive amounts of current like some Li-Ions and NiCads.

For your application, the 2000 to 2500 mAH AA batteries would work ok. They aren't too expensive and easy to charge. The other option would be the high capacity Li-Ion/Li-Poly's. These are better in many ways but are more expensive and need a specific charger.
Check out tenergy.com or batteryspace.com. I've bought batteries from both...

[robaxman]

Cool, thanks for the comments so far.

To make sure I have this straight, LiPoly will give me higher instantaneous power than NIMH. This isn't so important because my platform isn't really meant to pull high current values since it isn't supposed to be moving too quickly at any given point. So if I am not concerned with the weight of the batteries, then the NIMH will be better because of the cost difference. From what I've read, NIMH can also have more charge cycles than the LiPoly, so they will be even cheaper over the full lifetime of the batteries (the full amount of time I get to use the same batteries without throwing them away, not the amount of time I get to use the batteries on a single charge) than the LiPoly.

It looks like Ni-Cads would get even more charge cycles than the NIMH, my main concern with the difference there is the environmental one when it finally comes time to dispose of the batteries.

Probably what I will eventually do is buy both NIMH and LiPoly and just keep charging records and use records and see which works best. But I will probably start with the NIMH to get moving.

[HarryBotter]

Probably what I will eventually do is buy both NIMH and LiPoly and just keep charging records and use records and see which works best. But I will probably start with the NIMH to get moving.

That's probably not worth doing, remember that you need different chargers for both. Energy density is higher in the LiPOs than the NiMHs, the only downside to the LiPOs is cost and temperament. You just have to be more careful with them, although I've had NiMHs burn up too. Work is ongoing to develop safer Lithium chemistries, see the threads at:

http://www.botmag.com/forum/showthread.php?t=272
http://www.botmag.com/forum/showthread.php?t=243

[Kevin Berry]

And as far as environmental issues, remember we're talking about rechargable nicads, not disposable. So whichever kind you buy, there is an environmental end game to be played. If thats a key constraint to you (and I admire your thoughfullness) you might work backwards with some research on "battery recycling" and see what's friendliest. Let us know, thats an interesting topic.

[robaxman]

And as far as environmental issues, remember we're talking about rechargable nicads, not disposable.

Yes, I am aware that the nicads are rechargeable. But, unfortunately, they can only be recharged so many times then something is done with them.

So whichever kind you buy, there is an environmental end game to be played. If thats a key constraint to you (and I admire your thoughfullness)

It is important to me, yes. And that is why I ask. There is an endgame to be played. Unfortunately, I can't be entirely green and play with robots, electronics have to be manufactured, I need power to recharge batteries, etc, but I at least want to minimize what I can.

you might work backwards with some research on "battery recycling" and see what's friendliest. Let us know, thats an interesting topic.

From what I have read, NIMH is better than nicad as cadmium is nasty stuff. Lead is known to be nasty as well. NIMH still uses some heavy metals, as do Li-ion batteries.

Apparently, though, lead recycling from batteries is one of the recycling success stories...

http://www.batterycouncil.org/recycling.html

Though all rechargeable batteries are recyclable...

http://www.rbrc.org/call2recycle/consumer/consumer_faq.html

Of course, I am sure there are waste products from the recycling process, but delving into all of that would probably take more time than I have to spend on it. I want to build my bot, not just think about it.

What looks interesting to me is the links given earlier...

http://www.botmag.com/forum/showthread.php?t=272

The M1 “nano phosphate” lithium ion cells sound interesting. They don't seem to need the caution of regular LiPoly. As for their environmental impact

http://www.a123systems.com/html/tech/safety.html

has some interesting info, though admittedly it is in an ad. Seems like the fewer heavy metals used, the better. Of course, these batteries are pricey, but they can supply a lot of power, much more than I need. But maybe that just means I don't need to recharge as often. I am leaning towards these right now. Hopefully my motors won't care too much about 13.2V instead of 12V. Doesn't seem like an unreasonable amount over the rated voltage of the motors.

I never knew just picking batteries would be an adventure.

I appreciate all the comments. Thanks folks. Keep 'em coming if there are other points to be made.

[robaxman]

And as far as environmental issues, remember we're talking about rechargable nicads, not disposable.

Yes, I am aware that the nicads are rechargeable. But, unfortunately, they can only be recharged so many times then something is done with them.

So whichever kind you buy, there is an environmental end game to be played. If thats a key constraint to you (and I admire your thoughfullness)

It is important to me, yes. And that is why I ask. There is an endgame to be played. Unfortunately, I can't be entirely green and play with robots, electronics have to be manufactured, I need power to recharge batteries, etc, but I at least want to minimize what I can.

you might work backwards with some research on "battery recycling" and see what's friendliest. Let us know, thats an interesting topic.

From what I have read, NIMH is better than nicad as cadmium is nasty stuff. Lead is known to be nasty as well. NIMH still uses some heavy metals, as do Li-ion batteries.

Apparently, though, lead recycling from batteries is one of the recycling success stories...

http://www.batterycouncil.org/recycling.html

Though all rechargeable batteries are recyclable...

http://www.rbrc.org/call2recycle/consumer/consumer_faq.html

Of course, I am sure there are waste products from the recycling process, but delving into all of that would probably take more time than I have to spend on it. I want to build my bot, not just think about it.

What looks interesting to me is the links given earlier...

http://www.botmag.com/forum/showthread.php?t=272

The M1 “nano phosphate” lithium ion cells sound interesting. They don't seem to need the caution of regular LiPoly. As for their environmental impact

http://www.a123systems.com/html/tech/safety.html

has some interesting info, though admittedly it is in an ad. Seems like the fewer heavy metals used, the better. Of course, these batteries are pricey, but they can supply a lot of power, much more than I need. But maybe that just means I don't need to recharge as often. I am leaning towards these right now. Hopefully my motors won't care too much about 13.2V instead of 12V. Doesn't seem like an unreasonable amount over the rated voltage of the motors. And I get the weight advantage over the SLA batteries.

I never knew just picking batteries would be an adventure.

I appreciate all the comments. Thanks folks. Keep 'em coming if there are other points to be made.

[HarryBotter]

Hopefully my motors won't care too much about 13.2V instead of 12V.

Your motors won't notice the difference, they'll just run a touch faster.