# Society of Robots - Robot Forum

## Mechanics and Construction => Mechanics and Construction => Topic started by: SciOlyStudent on November 12, 2007, 04:06:56 PM

Title: Some noob questions about the 50\$ robot
Post by: SciOlyStudent on November 12, 2007, 04:06:56 PM
A few questions about the 50\$ robot tutorial...
1.  I own a 470 ohm and 1.5 K ohm resistors.  Can I use them in place of the 340 ohm and the 1.62 K ohm resistors?
2.  Is there a battery setup I could use instead of the 16.50\$ pack?  I do not have a lot of money.
3.  On the topic of batteries, what is the significance of mAh?  When you have multiple batteries, do you just add up each one, or does it stay constant (2 700mAh batteriess=1400 mAh or still 700mAh)?

I'm trying to be as cost effective as possible, so if you could list any other cost cutting techniques for the 50\$ robot that would be a great help (less expensive, but still as effective servos, for instance).
Title: Re: Some noob questions about the 50\$ robot
Post by: frank26080115 on November 12, 2007, 04:57:42 PM
1.
Link to the schematics please, but I'd say yes to the 340 ohm resistor (I'm guessing that it's for a current limiter for a LED)

2.
get a AA battery holder and AA batteries

3.
mAh is milliamps per hour
1mAh means you can use 1mA from the battery and the battery will last 1 hour
If you don't understand current, milliamps, or amps, it means you are still in school and should have a science teacher who can answer your questions.
when batteries are added in parallel, you add the mAh up, but when you add identical batteries in series, the voltage increases but the mAh stays the same.
Title: Re: Some noob questions about the 50\$ robot
Post by: Admin on November 12, 2007, 08:21:12 PM
Quote
I own a 470 ohm and 1.5 K ohm resistors.  Can I use them in place of the 340 ohm and the 1.62 K ohm resistors?
Yeap they will work fine.
Title: Re: Some noob questions about the 50\$ robot
Post by: SciOlyStudent on November 13, 2007, 02:43:28 PM
K, now as for the parallel vs. series setups.  I am assuming the jist is that paralell=more power quicker and series= less power over a longer time period, but what is it that makes them different?
Title: Re: Some noob questions about the 50\$ robot
Post by: Admin on November 13, 2007, 02:46:20 PM
example time!

two 6V 1000mAh batteries in series => 12V at 1000mAh
(sum of voltages)

two 6V 1000mAh batteries in parallel => 6V at 2000mAh
(sum of mAh, which relates to how long the battery lasts)

three 6V 1000mAh batteries in parallel => 6V at 3000mAh
Title: Re: Some noob questions about the 50\$ robot
Post by: SciOlyStudent on November 13, 2007, 02:53:14 PM
OoOoOoOo.... so is it that parallel has less power and lasts longer?  It just occured to me that the higher the mAh, the longer the battery life.  That being as it is, what would you suggest for the 50\$ robot?  And what is different about the setup of the batteries that makes it parallel/series?
Title: Re: Some noob questions about the 50\$ robot
Post by: Admin on November 13, 2007, 03:18:31 PM
Quote
what is different about the setup of the batteries that makes it parallel/series?
its how they are wired together, see my next point . . .

Quote
so is it that parallel has less power and lasts longer?
in terms of power, parallel = series, because power = voltage * current. The difference is that motors are stronger with a higher voltage, and certain electronics require a minimum voltage. just google for the difference for a good tutorial.

Quote
what would you suggest for the 50\$ robot?
Try calculating it:
http://www.societyofrobots.com/battery_calculator.shtml

Basically you enter what uses power, and then enter in your battery specs, and it will then calculate how long your robot will last.

Expect a servo to drain about .3A of current. Entering numbers in, it says the \$50 robot will last 1.5 hours straight on a 6V 1000mAh battery.
Title: Re: Some noob questions about the 50\$ robot
Post by: SciOlyStudent on November 13, 2007, 03:50:06 PM
More on batteries...I have a charger that has an about of 6V DC at 300mA, but it says for use on NiCad batteries...Is the mA too high and is it okay to use it on NiMH batteries?
Title: Re: Some noob questions about the 50\$ robot
Post by: Admin on November 13, 2007, 03:55:59 PM
Maybe . . . check the NiMH battery datasheet for maximum charging current . . .