Best battery for a robot?

[Blind_squirrel]

So after a long time, my robot project has finally lifted off. Now in the final steps (adding battery and motors to the frame), I need some help choosing the battery. I am using the adafruit motor control board with the arduino uno.

https://www.adafruit.com/products/50 - Arduino
https://www.adafruit.com/product/1438 - Motor controller

I plan on using 4 dc motors (at least 5 volt, as the board requires), and I am no good with electricity. If I have four 5 volt dc motors will I need a 20 volt battery? If so, where can I get a battery this size that is rechargeable? Preferably under $25, for this project is drawing near the end of its budget.

[adafruit_support_mike]

The motors will run in parallel, so you only need a 5v battery. You need one that delivers enough current to run all the motors and hardware at the same time though.

What motors are you using?

[Franklin97355]

What are the specs on the motors you plan to use?

If I have four 5 volt dc motors will I need a 20 volt battery?

No, the voltage stays at 5V but the more motors you add the more current you will need to run them at full power.

[Blind_squirrel]

What motors are you using?

http://www.ebay.com/itm/5-Pieces-DC-3-6 ... 48698f777d

with

http://tinkersphere.com/motors-wheels/3 ... ible-.html

***

Thanks for the advice! I know it was a really clueless question, but I'm learning!

[adafruit_support_mike]

Hey, the more questions you ask as a beginner, the faster you can get on to asking questions as an expert. The asking never stops, it just depends how far you have to go before you find someone who knows the answer. ;-)

The motors you linked fall into the general heading of 'hobby motors', so I'll assume they're similar to the ones we have in the shop: https://www.adafruit.com/products/711

Those use between 70mA (no load) and 500mA (shaft held so it can't rotate), so I'm going to wave my hands a bit and assume that each motor will want about 300mA.

If you have four motors, the expected current will be about 1.2A, with 2A being the worst case.

For that kind of current draw, AA batteries will probably be your best bet. They can deliver about 2A, they hold enough energy to run for an hour at that level of current, they're cheap, and you can get them just about anywhere.

A 4-pack of AAs will give you a 6v supply that you can plug into an Arduino's DC barrel jack, and will give the motors a little more strength.

We have a 4-AA battery holder with an on/off switch in the shop (https://www.adafruit.com/products/830), and a 2.1mm barrel plug with terminal blocks that can connect to any kind of wiring (https://www.adafruit.com/products/369).

[Blind_squirrel]

For that kind of current draw, AA batteries will probably be your best bet. They can deliver about 2A, they hold enough energy to run for an hour at that level of current, they're cheap, and you can get them just about anywhere.

A 4-pack of AAs will give you a 6v supply that you can plug into an Arduino's DC barrel jack, and will give the motors a little more strength.
.

Mike,
I tried what you suggested and used 2 battery packs. One for motors and one for sensors. The battery packs were drained extremely fast, and when any resistance was added to the motor, the power draw jumped over 6 volts. Is there any way to use a rechargeable USB pack that is used to charge phones? My idea was to solder two usb cables together at the power and ground and then connect a wire from the motor board to the USB cables and insert the USB cables into the battery. In essence, the batterys would combine to make 10 volts and I could use the adafruit 4.5 to 9 volt motors.

[adafruit_support_bill]

the power draw jumped over 6 volts.

Do you mean 6 amps? The voltage usually drops under load. Can you post a photo of how you took that measurement? Also, a photo or two of your robot so we have a better idea of how the motors are being used.

[Blind_squirrel]

the power draw jumped over 6 volts.

Do you mean 6 amps? The voltage usually drops under load. Can you post a photo of how you took that measurement? Also, a photo or two of your robot so we have a better idea of how the motors are being used.

I can only seem to get one photo added, but here is the voltage meter I used. I touched the leads to the pins on the DC motor while it was running and when I added torque. You were right, I was measuring in amps, but when I tried to measure it again it was instead 1 amp to 2 amps.

Here is the picture of how I have it set up.

DC motor attached to usb battery

Capture.PNG (731.35 KiB) Viewed 185 times

[adafruit_support_bill]

I touched the leads to the pins on the DC motor while it was running and when I added torque. You were right, I was measuring in amps, but when I tried to measure it again it was instead 1 amp to 2 amps.

You can't measure current that way. You need to insert the meter into the circuit. See this guide for details: https://learn.adafruit.com/multimeters/current

One thing that stands out in your photo is the unprotected solder joints look like they are touching. This would cause a direct short circuit across the battery - potentially damaging the battery. You should insulate those joints for safety.