Let's Make Robots!

Power Issue Solved

Quote of the day:

Is my robot a cyborg, becouse it has blood sweat and tears into it?

Hello everybody,

Yesterday I put this robot together, but it has a power issue.

Robot UNO Rev3

I used the script that was written for the german SH Robot.
The following happens after giving the motor shield 6 Volts (4x AA):
It tries to do everything it's supposed to, but only if I keep it in the air. As soon as I put it to the ground it barely goes forward.
Now I'm only giving the motor shield power, but as soon as I connect the bot tho the computer by the USB cable to upload software, it has more power. So I wondered, can I plug in a 9V (6AA) battery pack to my Arduino UNO to solve the lack of power problem, or will this fry the board?

This is how the wires are connected at the moment:


Only 4AA batteries (bought them today) to the Motor shield.

As mentioned in the earlier Blog, it's also possible that the motors are to heavy. These geared motors came along with the kit, and has the following written to it:

DAGU Robot DG01D 48:1

Forgive me if I'm asking stupid questions, I'm only working three days on this and that's including ordering parts, reading on this website and assembling the machine. What's logic to you might still be abracadabra for me.

So how to solve this?

Greetings,

Albert.

P.S. I know it's a kit, but first I want the hardware to be setup in the right way, before putting it into a more original case ;-)

And the story continuous...

After getting some useful advice from different members I solved the problem. Instead of the 6V battery pack, I installed a 9V battery pack. Currently fitted with 6 1,5V standard batteries, but with the intention to replace them later on with 1,2V NiMh batteries. I connected the 9V battery pack to the Arduino Motor Shield V3 directly and nothing else to the UNO. Next thing is to learn some basic programming, so I can solve the problem with my sensor (script is for a Sharp 4-30 and mine is a Sharp 10-80). To be continued! And thank you all for all the kind replies.

Albert.

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Thanks for the quick response. These are interesting facts. So if I understand it correctly, NiMh Batteries are 1.2 Volts, so in that case I have to use an 5 X AA Battery case to get the desired 6 Volts for the motors and then the power source wil be more continious... But the 6V will probably still not be enough to make everything run smoothly. Perhaps it's possible, to use the 6 Volt pack for the Motor shield and should I use a seperate power source of 9V for the Arduino Uno itself. Is it possible to just plug in a 9V Battery Pack to the Arduino UNO V3 while it is conected to the Arduino Motor Shield V3 with a 6V battery pack connected at the same time? Or wil I fry the whole thing? What I intend to say is: Wil I have seperate circuits, or Will it be 6V + 9V = 15V and a lot of smoke? ;-)

Then the next problem wel be how to create 9V with NiMh batteries. For 6V it's easy, just add one more battery, but for 9V it's 7 batteries to create 8,4V but 8 will give you 9.6V...

I agree with 6677, Basically 6x 1.2V NiMh batteries should be perfect.

The Arduino UNO claims a minimum input voltage of about 7.5V because that's what the voltage regulator datasheet specifies but that is the minimum voltage required for the regulator at it's rated load. The Uno draws far less current so 7.2V is good.

The voltage rating of the motors is a maximum continuous voltage rating. Robots almost never travel at full speed for great lengths of time so do not be afaid to exceed the voltage rating a little bit. Your motor shield will loose some voltage anyway.

In cases where your battery voltage is much higher than the motor voltage then you can limit you maximum PWM to deliver the same amount of power to the motor. Power = voltage x current.

If you do manage to power the motor shield and arduino seperately, one of those 9v batteries for a fire alarm will serve the arduino fine (they are entirely useless for anything else though).

 

Otherwise. There is actually a voltage drop on the motor driver, stick 6v in and it will probably be 4 or 5v going to the motor. I would just go with a 7.2v battery shared for both. The motors will probably cope perfectly fine.

G'day Albert :-)

Power is often a problem for beginners. Usually because they know about volts but not current. It sounds like your robot is lacking both.

To begin with, 4xAA with alkaline batteries will only provide 6V which is not really enough for the Arduino and depending on the motor shields voltage drop will probably be a bit low for the motors.

A big problem with alkaline batteries is they have a relatively high internal resistance which limits their maximum output current and will cause the voltage to drop when you draw too much current. Their voltage will quickly drop as they discharge so unless they are new batteries then the voltage will be too low anyway.

If your batteries are NiMh then you only have 4.8V to begin with which is too low for everything. NiMh are the best battery for small robots because they can deliver much higher currents and maintain a constant voltage for about 90% of the discharge cycle.

No matter which battery your using you will probably need to go to a 6x AA battery pack.

 

I suggest you look here: http://batteryuniversity.com/ to learn mor about the different types of batteries.
Then look here: http://letsmakerobots.com/node/3880 to learn more about robot power supplies.