battery / power question

By guibot
2008-08-19 11:43

hi!

my first post here!!

i´m glad to find letsmakerobots!!!!!

i´m an electronics newbie, i´ve made my 1st robot wich i´ll post photos as soon as i find out how to create a blog entry :)

now, i´ve started a new project, wich is an offroad car, and i want to add brains (arduino) and some sensors (ultrasonic and infrared).

the first problem is, i´m using 9v batteries, and the steering motor seems to need more power, a noise comes out and it only moves a little..

i´m looking for an advice in wich kind of batteries should i use!

I´m using one battery to power the arduino and other battery to power the motor shield (adafruit).. so i don´t know what to do ... :)

good power setups will also be welcome!! :)

thanks and best regards

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By anachrocomputer @ Tue, 2008-08-19 12:20

How about NiCads?

How about using the same type of Nickel-Cadmium batteries that are used with radio-controlled racing cars? They're usually rugged and powerful enough for this sort of thing. And you can get fast chargers from the same suppliers who deal with R/C model parts. Those little 9V rectangular batteries are really tiny in terms of power available. The six cells inside are smaller than AAA cells, which should give you some idea!

http://www.flickr.com/photos/anachrocomputer/1304805314/

http://www.flickr.com/photos/anachrocomputer/1303941393/

Try to get a NiCad or NiMh pack with C-size cells. But beware of accidentally shorting the battery -- fit a fuse of some sort, because bigger batteries can supply large currents in fault conditions.

By guibot @ Tue, 2008-08-19 12:41

hi!! thnx for replying

hi!! thnx for replying :)

those are a really tiny batteries inside of 9V case!!!

i´m looking into this one http://aliatron.com/loja/catalog/product_info.php?cPath=49&products_id=337

its a 9,6V, maybe too much power!! i´ll try to find a 7.2V...

if i use a fuse, should i put it between the VCC cable? can you tell me what kind of fuse should i use?

is it a good practice to use voltage regulators?

By anachrocomputer @ Tue, 2008-08-19 13:32

NiCads

Yes, those NiCads are OK, although at 2000mAh, they're AA size not C size. As for the voltage, that depends on what your motors and servos need in your robot. Do you know the voltage rating of the steering servo that you mentioned?

The fuse usually goes in series with the positive power wire from the battery, before any other parts. That way, there's the minimum length of unfused wire present to cause shorts if something goes wrong.

And voltage regulator are good, if your ciruit requires regulated power. Large motos probably don't need it, but electronics stuff like microcontrollers does. Best to have separate batteries for big motors. Use one battery pack for the electronics, and another (bigger) for the motors and servos. You'll need a few volts extra in the battery to feed the input of the regulator. Fit it with a heatsink, and fit the capacitors on input and output. Look for 7805 circuits for a 5V regulator, 7812 for 12V and so on. Don't build it like I did, though!

http://www.flickr.com/photos/anachrocomputer/293677470/

By guibot @ Tue, 2008-08-19 17:35

I see!! Must take a look

I see!!

Must take a look into those circuits.

The sterring motor i blelieve it is not a servo, at least it doesn´t look like a regular servo (black case) , it looks like a standard DC motor, if i push the 9V battery wires directly into the motor (little plugs) it steers fully. Its rotation seems to be locked by some plastic part, so it only rotates for 45º (+-) for each side.. i hope my english is clear enough..

more photos below

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By chopperdave @ Wed, 2008-08-20 07:27

I second anachrocomputer's

I second anachrocomputer's suggestion to use rechargeable batteries.

NiCd, NiMH are simple and relatively safe batteries, and can be found cheap! It is safe to charge these batteries at C/10 (for example, a 1000mAh battery at 100mA.) You don't even need a specialized charger. Just use a wall wart with an appropriate voltage and current rating, and keep an eye on things with an ammeter.

LiPo batteries store more energy for a given mass, but they can be dangerous.

Some rechargeable batteries can deliver a LOT of current, so be careful with that steering motor. Even though you used a 9V battery to make the steering go, a similar voltage rechargeable batteryk might burn it up quickly, since the rechargeable battery can supply so much more current!

By guibot @ Wed, 2008-08-20 09:29

hi chopperdave!

hi chopperdave! thank you for commenting!

i´m on my way to the store to get the batt... :)

When you say to be careful... i still have some doubts about what should i do so i make things safer, i don´t want to burn this motor (at least at this stage).. what do you think it would be a safe workaround to do?

By chopperdave @ Wed, 2008-08-20 16:03

You could try starting with

You could try starting with a low voltage and working up to a higher voltage. Start with just 2 or 3 NiMh/NiCd cells in series and see how that works for the motor. Increase the voltage 1 cell at a time until you get the performance you want, and then make sure the motor isn't getting too hot or emitting any strange smells.

When you build your circuit to control this, you might want to set things up so that power cannot be continuously applied to the motor for too long.

In my area NiCd cells are not readily available, and NiMh cells vary widely in price! I recently bought a 20 pack of NiMh AA cells for $20, but I've seen similar cells for more than $5 each! I suggest you shop around.

That looks like a good platform for arobot! I'm going to have to scour thrift shops for a suitable RC car.

I'm looking forward to your update.

By anachrocomputer @ Wed, 2008-08-20 17:16

Build up voltage

I agree with the idea of building up gradually from a smaller voltage until the steering motor works properly. Note that you need not use NiCad/NiMH cells, but you can try out the motor with ordinary AA alkaline cells. Remember, though, that alkaline or zinc chloride cells are 1.5V each, while NiCads and NiMH cells are nearer to 1.2V each. If you need an intermediate voltage, you can get adjustable voltage regulators such as the LM317 and the LM2941. These devices can be adjusted to any voltage by the choice of a pair of resistors.

By guibot @ Wed, 2008-08-20 19:30

That is for sure a good

That is for sure a good begin! Thank you both!!

I have here several alkaline rechargable AA batts, so i will perform some tests and see the motor behavior.
I´ll also go tomorrow to the electronic store and see those voltage regulators.

One thing that crips me is, why doesn´t the steering motor spins when the voltage comes from the arduino shield?
Because if the voltage is applied directly from the 9V batterty it works properly!

By guibot @ Wed, 2008-08-20 20:23

I´ve tried with 6 batts,

I´ve tried with 6 batts, and it seems to steer a little more :)

now, this case is only for 6 batts, and i have 4 more to add, is there any correct way to do this? sorry for the newbie question :S

By guibot @ Wed, 2008-08-27 10:18

hi!!you might want to ake a

hi!!
you might want to take a look at the video :)
http://letsmakerobots.com/node/1795