Author Topic: 50$ robot power supply  (Read 3399 times)

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Offline gamefreakTopic starter

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50$ robot power supply
« on: January 08, 2008, 09:31:29 PM »
I notice in the tutorial you say either use a RC pack, or a 9 volt battery and a 6 volt pack, why?

Why not just use a 9 v battery?
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Offline ed1380

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Re: 50$ robot power supply
« Reply #1 on: January 08, 2008, 10:01:15 PM »
option 1- 6v pack for controller board and servo
option 2- 9v for controller board and 6v for servos

reasons- 6v or 9v will be regulated down to 5v for the controller board. and servo's will burn up with more than 6v
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Offline gamefreakTopic starter

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Re: 50$ robot power supply
« Reply #2 on: January 09, 2008, 06:45:22 AM »
so then dont use a 4 AA battery pack without the 9 volt because it has a low voltage/drains quickly?
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Offline ed1380

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Re: 50$ robot power supply
« Reply #3 on: January 09, 2008, 06:52:34 AM »
4AA=6v

except rechargable AA are 1.2v each=4.8v (will still work)
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Offline gamefreakTopic starter

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Re: 50$ robot power supply
« Reply #4 on: January 09, 2008, 07:05:29 AM »
so then why a 9 volt with the battery pack?
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Offline Crooksie

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Re: 50$ robot power supply
« Reply #5 on: January 09, 2008, 10:57:22 AM »
If I'm not mistaken the 9V battery is required to run the micro controller board.  The micro controller needs a regulated voltage supply, so a 5V regulator is used, the the voltage regulator has a drop of a couple of volts, so at least 7V ish needs to be supplied to it.  So you need the 9V battery to run the regulator because the 6/4.8V from the AA battery packs don't have enough voltage to run the regulator.

Hope that helps.

Offline Ro-Bot-X

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Re: 50$ robot power supply
« Reply #6 on: January 09, 2008, 11:42:45 AM »
4AA=6v

except rechargable AA are 1.2v each=4.8v (will still work)

4.8V is not enough to power both electronics and servos. Both will work if they are powered separatelly win 4.8V. But if they are powered by a single pack of 4.8V there will be problems. When the motors switch directions, a power drop will occur and the microcontroller will reset. To avoid that, big capacitors (over 1000uF) have to be installed in parallel with the battery pack. But the voltage will drop quickly and will not be enough for the electronics to work properly. So this setup has to be avoided.

Use at least one five cell NiMH battery (6V) pack to power your robots!

Edit: I have corected a typing mistake ed1380 found...
« Last Edit: January 09, 2008, 04:09:49 PM by Ro-Bot-X »
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Offline Admin

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Re: 50$ robot power supply
« Reply #7 on: January 09, 2008, 11:53:41 AM »
Why a 9V cannot power your servos: the 9 volt cell typically has 130-150 mAh, whereas a decent 4.8/6 volt NiMh AA pack has 1000-2500 mAh.

At 130mAh, your robot will last about 15 minutes before the battery needs to be replaced.

Offline ed1380

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Re: 50$ robot power supply
« Reply #8 on: January 09, 2008, 03:00:55 PM »
4AA=6v

except rechargable AA are 1.2v each=4.8v (will still work)

4.8V is not enough to power both motors and servos. Both will work if they are powered separatelly win 4.8V. But if they are powered by a single pack of 4.8V there will be problems. When the motors switch directions, a power drop will occur and the microcontroller will reset. To avoid that, big capacitors (over 1000uF) have to be installed in parallel with the battery pack. But the voltage will drop quickly and will not be enough for the electronics to work properly. So this setup has to be avoided.

Use at least one five cell NiMH battery (6V) pack to power your robots!
motors and servos?

i thougt the $50 robot had servo's only
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Offline Ro-Bot-X

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Re: 50$ robot power supply
« Reply #9 on: January 09, 2008, 04:11:24 PM »
I meant electronics and servos (or motors)...
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Offline gamefreakTopic starter

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Re: 50$ robot power supply
« Reply #10 on: January 09, 2008, 06:44:26 PM »
ok then, so the 9 volt will kill the servos, the 4.8 cant do anything and the 6 is just right, now i get it, thanks.

So now i have a new question, as it turns out all i have is 7.2 volt battery packs, and they use the all amazing NiCd technology, so would it hurt my servos to use this battery pack with the current schematic(the rc pack one).
« Last Edit: January 09, 2008, 07:50:48 PM by gamefreak »
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Re: 50$ robot power supply
« Reply #11 on: January 10, 2008, 05:57:23 AM »
7.2V will kill most servos too :P

Offline gamefreakTopic starter

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Re: 50$ robot power supply
« Reply #12 on: January 10, 2008, 06:34:27 AM »
stupid wimpy electronics, cant handle the amazing power of 1.2 volts over its optimmum

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Offline airman00

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Re: 50$ robot power supply
« Reply #13 on: January 10, 2008, 06:52:58 AM »
7.2V will kill most servos too :P

after a while ( meaning not instantaneous )   ;)
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Offline paulstreats

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Re: 50$ robot power supply
« Reply #14 on: January 10, 2008, 07:38:22 AM »
Just dont do it.

Whats more expensive. Afew batteries or constantly replacing your servos

Offline gamefreakTopic starter

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Re: 50$ robot power supply
« Reply #15 on: January 10, 2008, 10:56:09 AM »
During school an idea hit me, why not use the regulated power for the servos? will the current drain be over an amp? or will it cause a short power down screwing up the sensors? somethign along those lines?
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Offline airman00

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Re: 50$ robot power supply
« Reply #16 on: January 10, 2008, 11:06:42 AM »
Quote
Regulating Voltage to a Servo
As you should already know, servos have a voltage rating. Go above that voltage and your servo overheats and possibly fries. So suppose you have a 7.2V battery and you want to use a 5V regulator to power your servos, is that a good idea?

Short answer: No!

Longer answer . . . it will work, but its a huge waste of battery power.

So lets say you have your 7.2V regulated to 5V and the servos draw a total of 1.5A of current.

Wasted power is:
(7.2V-5V)*1.5A = 3.3W

Percentage wise, its
(7.2V-5V)/7.2V = 30.6%

Thats the battery energy percentage wasted to thermal heat - almost 1/3rd!!!

Speaking of heat, your voltage regulator probably has thermal shutdown, meaning that if it overheats it will throttle down current to your servos - meaning your servos will have lower torque and lower speed. If your voltage regulator doesn't have thermal shutdown, it will just fry instead (not a good thing).

But if you still really really need to regulate for servos, get a switching regulator (like ~83% efficiency on average).

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Offline gamefreakTopic starter

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Re: 50$ robot power supply
« Reply #17 on: January 10, 2008, 11:17:30 AM »
ok then, I guess this weekend im going shopping.

BTW. why is all that in qoute?
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Offline paulstreats

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Re: 50$ robot power supply
« Reply #18 on: January 10, 2008, 11:22:52 AM »
its from another topic about the same thing

Offline Admin

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Re: 50$ robot power supply
« Reply #19 on: January 10, 2008, 12:50:39 PM »

 


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