Author Topic: Batteries for 50$ robot (Read 4885 times)

SciOlyStudent · « **on:** November 23, 2007, 10:50:49 AM »

I'm trying to save some $$ while building the 50$ robot. Batteries are a huge expense and I was wondering if it is okay to use digital camera batteries. Just a precaution, so I don't go and buy them without making sure they'll work, thanks

.

airman00 · « **Reply #1 on:** November 23, 2007, 10:53:35 AM »

which digital camera batteries?

those tiny 12V ones?

Don't get those , they'll run out very quickly

stick with the instructions

($50 is not that much)

SciOlyStudent · « **Reply #2 on:** November 23, 2007, 02:24:08 PM »

Well, the robot costs a little more than 50$ (so far I'm almost at 70$), but now I have another question. I bought 4 1.2V 2000mAh batteries and my pop has an "ahem" ancient charger for all sizes of batteries. It has a warning label that says "WARNING: CHARGE ONLY NICKEL CADMIUM BATTERIES..." and my batteries are NiMH...
I'm under the impression that I can use this charger because it charges at 1.45V at 200mA (which I believe I read somewhere that this is okay). Will it work or will it explode my batteries? Also, is it possible to run the entire robot off of 4 AAs, instead of 4 AAs and a 9v? Thanks

. And to airman00, yes it is a lot of money seeing as I have absolutely no means of income.

HDL_CinC_Dragon · « **Reply #3 on:** November 23, 2007, 05:35:23 PM »

If im not mistaken, you cant use that charger. Since NiMH and NiCd batteries have different chemical compositions they cannot be charged the same way...

And why didnt you just buy the 6volt battery pack?

The robot does in fact cost more than $50. I spent just over $100 on mine... not including the SharpIR sensor that I upgraded to.

Oh, and no, you cant run the whole thing off of just 4AA batteries. The circuitry will run off the AA batteries but the servos need more thus the 9 volt.

SciOlyStudent · « **Reply #4 on:** November 23, 2007, 06:49:22 PM »

Is it possible to run both servos off of another set of 4AAs? I'm going to modify this robot to use in a competition and it has limits on the amount off voltage a single battery can have on your robot (no more than 1.5V for each single cell or 4.8V in a single battery pack). This is why I didn't just get the battery pack, I would be breaking the rules...
Any suggetions

.

SomeSaba · « **Reply #5 on:** November 23, 2007, 07:59:36 PM »

hi, im doing this event too!

bottom line: yes it will work

You can run your servos straight off the battery because servos are rated from 4.8-6volts, and fully charged ur 4.8pack should be seeing around 6volts anyway, which is okay for a 5volt regulator that prob has around a 1volt drop. It just means your batteries have to be topped off, which isnt cool

Admin · « **Reply #6 on:** November 23, 2007, 08:07:55 PM »

About the battery charger question, check the datasheets. NiCad batteries can typically be charged at higher rates than NiMH, so a NiMH on a NiCad charger would probably fry. However, battery tech changes fast so this might not be true for your particular NiMH batteries. Check the datasheet for the maximum charging rate on your NiMH, and see if the charger charges at less than that rate.

Quote

Oh, and no, you cant run the whole thing off of just 4AA batteries. The circuitry will run off the AA batteries but the servos need more thus the 9 volt.

You got that backwards. What you meant to say was:
"Oh, and no, you cant run the whole thing off of just 4AA batteries. The servos will run off the AA batteries but the circuitry needs more thus the 9 volt."

SciOlyStudent · « **Reply #7 on:** November 23, 2007, 08:11:23 PM »

Ummm.... I'm not sure if I follow... your saying that because of the 5V regulator the pack has to be at full charge in order to supply enough power to the servos? Is there any way to change this with a minimal amount of buying more batteries or parts? Geez, what a headache

!

Admin: What data sheet? Are you referring to something on this site? I checked the battery case and all it said was "Charge with chargers recommended for NiMH batteries"...

Admin · « **Reply #8 on:** November 23, 2007, 08:32:27 PM »

Quote

Admin: What data sheet? Are you referring to something on this site? I checked the battery case and all it said was "Charge with chargers recommended for NiMH batteries"...

Hmmmm there should be a part number or some type of label on the battery. Just google that label and look for specs on the battery. If you can't find any info on it, my guess is as good as yours.

SciOlyStudent · « **Reply #9 on:** November 23, 2007, 10:26:22 PM »

Ok, found the data sheet (Radio Shack seems to like to hide it)... It says that it charges at 1.5V 180mA, and my charger says 1.45VDC 200mA. Will the difference of 20 cause a catastrophic explosion?, Will our intrepid hero ever solve his battery problems? Tune in next post for the answers (hopefully

).

SomeSaba · « **Reply #10 on:** November 23, 2007, 11:16:42 PM »

Its because the voltage regulator for the the mega168 needs to have an input voltage above 5volts, and since your battery is 4.8volts total it wont make it.

But under the rug....the batteries fully charged are hopefully around 6volts which should be enough to give you an output of around 5 volts for the IC.

But im worried about this...

i havent read the rules over too carefully, it would be better if u have 4 cells just for the regulated circuitry (maybe some regular AA's from the store) and use ur rechargables for just the servos to avoid any problems.

Ro-Bot-X · « **Reply #11 on:** November 24, 2007, 01:54:20 AM »

The Low Drop Out voltage regulator lets the voltage go unregulated if is lower that 5.5V. But you will find that the electronics circuitry is not stable for low voltages. Fully charged, the NiMh batteries will work well, but the voltage will drop soon and your robot may not work as espected. So a pack of 4 NiMh batteries (4.8V) will power your robot for a smaller amount of time than a pack of 4 Alkaline batteries (6V). But a pack of 5 NiMh batteries (6V) will work perfectly.

Admin · « **Reply #12 on:** November 24, 2007, 09:09:06 AM »

Quote

Ok, found the data sheet (Radio Shack seems to like to hide it)... It says that it charges at 1.5V 180mA, and my charger says 1.45VDC 200mA. Will the difference of 20 cause a catastrophic explosion?, Will our intrepid hero ever solve his battery problems? Tune in next post for the answers (hopefully ).

lol
hmmmm it will work, but not sure if it will damage your battery at all. the damage occurs from overheating during the charge. when you charge your battery, keep it in a cool/cold area and it should be fine.

SciOlyStudent · « **Reply #13 on:** November 24, 2007, 09:59:25 AM »

Ok, thanks for all the help. Is there any cheap way to supply enough power to the circuitry? I can't use more than 8 batteries total because of the competition. I do have a pair of old cordless phones that are NiMH and have 3.6V, but only 650mAh... could I use these two batteries for the whole robot or will it run out of power to fast? Also, is there any such thing as a NiMH 1.5V battery? If I could find 4 of those, it would be enough to power the bot right? I'm only allowed to use 4 batteries (<,=1.5V each) or one battery pack (<,=4.8V) at a time. Any help

?

Admin · « **Reply #14 on:** November 24, 2007, 10:09:34 AM »

Quote

could I use these two batteries for the whole robot or will it run out of power to fast?

try entering in your robot info and calculate it:
http://www.societyofrobots.com/battery_calculator.shtml

It appears the rules ban you from using more than 4.8V, right? . . . this is really odd to me since its the bare minimum most robots need to work. (but Im confused since you said 8 batteries, then you say 4 later)

But don't worry - microcontrollers can work as low as ~3V (check the datasheet). Design all your electronics to work at 4.8V and everything will be fine. You just need to change out one component - the voltage regulator - to output somewhere around 4V.

Ro-Bot-X · « **Reply #15 on:** November 24, 2007, 10:19:29 AM »

Quote from: SciOlyStudent on November 24, 2007, 09:59:25 AM

I'm only allowed to use 4 batteries (<,=1.5V each) or one battery pack (<,=4.8V) at a time. Any help ?

If you only are allowed to use one pack of batteries for both electronics and motors, then use 4 Duracell batteries! What's the problem? You are building the robot for the contest, no? So you need 4 Duracells for testing and other 4 Duracells to have fresh batteries at the contest. NiMh batteries are for extended robot use, like if you build it for fun to play at home, then it will be a waste of money to use Duracells.

If you are allowed to use different battery packs for motors and electronics, the 4 batteries pack for the electronics can be Duracells and you don't need to change them at the contest. In this case, you can use a 4 NiMh cell pack for the motors, and charge it before the contest. That means 8 batteries total, you say you are allowed that.

SciOlyStudent · « **Reply #16 on:** November 24, 2007, 10:27:19 AM »

So I could use 4 alkalaine batteries to power the whole thing? I am going to make robots as a hobby at home, but that sounds like it would work fine for the competition! Oh, and the thing about the 8 batteries, 4 batteries thing, I read over the rules and it says I may IMPOUND 8 cells with my vehicle, but may only use 4 at a time... sorry about that. Is there any problem with just using akalaine? Thanks again for all the help

!

P.S. you guys are really quick to respond thanks

!!

Ro-Bot-X · « **Reply #17 on:** November 24, 2007, 10:50:30 AM »

I used to play with Lego Mindstorms. The RCX was powered by 6 AA batteries and even that I could use NiMh I prefered not to, because of voltage difference. The motors otput was limited to 500mA, so the fact that NiMhs would give me more amps it didn't matter. At the same aperage, the motors work faster/stronger at a higer voltage.

In the $50 robot, the servos will spin faster if you are using 6V to power them. Almost the same like in the Mindstorms case. So, to increase speed on your robot, use Alkaline batteries to power both the motors and electronics. Do this only for the contest. If you plan to use the robot at home many times, it is better to use NiMhs, because you can charge them as often as you use them. Think about this: the price for the NiMhs and charger will even out the price for about 6-8 sets of alkalines. For $19.99 you can find a charger and 4 NiMhs at Walmart...

ed1380 · « **Reply #18 on:** November 24, 2007, 11:47:39 AM »

Quote from: HDL_CinC_Dragon on November 23, 2007, 05:35:23 PM

Oh, and no, you cant run the whole thing off of just 4AA batteries. The circuitry will run off the AA batteries but the servos need more thus the 9 volt.

I say thats wrong. I did run my whole robot off 4 AA batteries.

also the servo's can't get more that 6v or they will likely fry. the board on the other hand has a voltage converter so you can use 9v.

what about energizer e2 lithium AA?

according to this it gets over 3000mah

Ro-Bot-X · « **Reply #19 on:** November 24, 2007, 12:50:55 PM »

A while ago I was working on a robot kit for beginners to introduce to people in Romania. The first version of the kit was using servos and a Nemesis microcontroller, but it was too expensive to be marketable. So the second version used a ATMega8 and DC motors, but I did not finalize it because of lack of a cheap motor source in Romania. (The electronics price was the same as the price for one servo!) Well, this is not important. What I wanted to say is that the robot worked perfectly with 4 NiMh batteries, but for less time as with 4 Alkaline batteries. To make the robot go faster, I used larger wheels. Here are some pictures of the first generation kit:

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Author Topic: Batteries for 50$ robot (Read 4885 times)