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### Author Topic: \$50 Robot query  (Read 1183 times)

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#### robaker

• Jr. Member
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##### \$50 Robot query
« on: February 20, 2010, 07:06:34 AM »
What is the appropriate voltage for the circuit ?
In case 1: Its written to provide 6V ( both for 2 servos and the circuit)
while in case 2 : 4.8 V for servos and 9V for circuit.
Thus, why 9V in case 2 why not 6V ?

#### Soeren

• Supreme Robot
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##### Re: \$50 Robot query
« Reply #1 on: February 20, 2010, 08:08:39 AM »
Hi,

Thus, why 9V in case 2 why not 6V ?
Because a PP3 battery is a small package and since you need 5V, you have to regulate it down.
A 9V battery goes down to 5.4V when flat.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

#### robaker

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##### Re: \$50 Robot query
« Reply #2 on: February 20, 2010, 08:31:47 AM »
if 5V is needed that could be obtained by 6V battery/supply as done in case 1 with 5xAA NiMH. plz if you could explain such concepts of voltages as for beginners may be beneficial.
Thank you for replying.

#### cyberfish

• Robot Overlord
• Posts: 163
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##### Re: \$50 Robot query
« Reply #3 on: February 20, 2010, 01:35:52 PM »
It's difficult to get 5V from a 6V battery because normal regulators (LM7805) require about 2V dropout (to provide a constant 5V, input needs to be above 7V).

To get 5V from 6V you will need a low-dropout regulator (LDO), which has weird output capacitor requirements to be stable, or a switching regulator, which also require external components, and are quite a bit more expensive.

#### Soeren

• Supreme Robot
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##### Re: \$50 Robot query
« Reply #4 on: February 21, 2010, 08:22:35 AM »
Hi,

if 5V is needed that could be obtained by 6V battery/supply as done in case 1 with 5xAA NiMH. plz if you could explain such concepts of voltages as for beginners may be beneficial.
5 NiMH cells are 5*~1.45V = ~7.25V when fresh from a charger and considered flat at 4.5V to 5.5V, depending on the current draw.
7.25 is way too much for the controller so you need to add (LDO) regulator.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

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