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Author Topic: Power supply for microcontroller and servos  (Read 1097 times)

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Offline fawnonyxTopic starter

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Power supply for microcontroller and servos
« on: October 13, 2012, 02:29:27 PM »
So I'm looking to build a 4DOF robot arm and am considering an Axon as a microcontroller. It would require at least four servos.
So just to confirm, running four servos at once doesn't mean I need 24 extra volts, it means the current draw is more and the batteries run faster right?
I also read the power regulation tutorial about using switching regulators to run the servos, but for the Axon it's apparently different, you just plug the servos straight into the digital ports and the axon supplies the power. So do I still need a switching regulator or does the Axon handle all the power stuff? Does the Axon supply 6 volts to every port or something?

Offline mike_522

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Re: Power supply for microcontroller and servos
« Reply #1 on: October 13, 2012, 03:26:57 PM »
combine them in parallel and they all gonna get same v, but the current draw will be very significant. With regards to tutorials, looking for them myself, especially clever ways how to prevent/protect my circuit from back emf of my motors, etc.

Offline lrmall01

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Re: Power supply for microcontroller and servos
« Reply #2 on: October 13, 2012, 08:27:18 PM »
Fawnonyx

Forgive me if you know this, but from your question it seemed you had kind of mixed apples and oranges.   A servo has 3 inputs - Signal, Power, GND.  The AXON will drive the signal to control the motion of the servo.  I don't think a switching regulator would be used to connect to the signal but I could see where a switching regulator could be used to supply the Power connection of the servo.  For a few servos, a linear regulator (LM7805 or similar) would be fine to power them.  Typically switching regulators are used for higher current draws.  Essentially you have to sum up the power usage for all your circuits and then design a supply suitable to power them.

Mike

Back EMF is handled in many cases with diodes to create a loop that lets the current bleed off from the coil in some manner.  I'm not as familiar with motors but that is the reason you see a diode sitting across a relay coil in most example circuits.
« Last Edit: October 14, 2012, 11:34:30 AM by lrmall01 »

Offline fawnonyxTopic starter

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Re: Power supply for microcontroller and servos
« Reply #3 on: October 14, 2012, 02:58:47 AM »
Well in the axon wiring tutorial video it showed all three servo wires being plugged into the axon digital port, so that means that the Axon is providing all the power to the servo, right? But the axon is usually powered with a single 6V NiMH battery pack, so how can it power four servos, or even the twenty some it is capable of connecting to?
Are you supposed to attach a separate battery and switching regulator to the "power bus" or something on the axon, which separately powers the servos?

Offline Soeren

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Re: Power supply for microcontroller and servos
« Reply #4 on: October 14, 2012, 04:37:07 PM »
Hi,

For a few servos, a linear regulator (LM7805 or similar) would be fine to power them. [...]
The LM7805 is a 1A device, while each servo may draw up to 1.0..1.5A peak, so even a single servo may send the LM7805 into thermal shutdown (or worse).


Back EMF is handled in many cases with diodes to create a loop that lets the current bleed off from the coil in some manner.  I'm not as familiar with motors but that is the reason you see a diode sitting across a relay coil in most example circuits.
For a bidirectional DC motor, you need 4 diodes (and nothing like 1N400x, they're way too slow).
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

Offline Soeren

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Re: Power supply for microcontroller and servos
« Reply #5 on: October 14, 2012, 04:39:51 PM »
Hi,

Are you supposed to attach a separate battery and switching regulator to the "power bus" or something on the axon, which separately powers the servos?
Not for two servos, but read all the documentation, it should be in there somewhere.
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

Offline fawnonyxTopic starter

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Re: Power supply for microcontroller and servos
« Reply #6 on: October 15, 2012, 05:24:52 PM »
Ahhh after reading the datasheet again, I think I get it now. The board and analog inputs are all powered through the 5V linear regulator while the digital I/O is next to a power bus that connects directly to the battery (unregulated). Thus I can connect the battery to a switching regulator then take that output and put it in the Vin and that will take care of the current high current draw from multiple servos.

Since the axon seems a little expensive for me and perhaps more complicated to program, I've been looking at alternate microcontrollers such as arduino. However arduino boards don't have convenient power buses like the axon, so are there any solutions to this besides making your own?

Offline angad

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Re: Power supply for microcontroller and servos
« Reply #7 on: November 03, 2012, 09:48:56 AM »
how can i use 7805 to generate 10 V power supply for my robot.
Is the output of 7805 equals to 5V +voltage applied to 2nd pin of 7805
Regards
Angad

Offline Admin

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Re: Power supply for microcontroller and servos
« Reply #8 on: November 06, 2012, 01:34:30 PM »
You don't need any form of regulator for the Axon.

Just plug in a 6V battery, and directly plug in the servos to the digital output pins, and you're done ;D

Programming the Axon isn't as hard as you think. Have you tried out Project Designer for WebbotLib yet? You just drag and drop what you want (ie servos, sensors, etc.), tell it to write the sample code for you (generate), and then you're done.

Details are in the tutorials, demonstration videos, and documentation.

Watch these:
http://www.youtube.com/results?search_query=axon+webbotlib&oq=axon+webbotlib&gs_l=youtube-reduced.3...551.2497.0.2655.14.14.0.0.0.0.127.987.11j3.14.0...0.0...1ac.1.TlYjlb736y8

Offline lrmall01

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Re: Power supply for microcontroller and servos
« Reply #9 on: November 06, 2012, 10:01:21 PM »
However arduino boards don't have convenient power buses like the axon, so are there any solutions to this besides making your own?


The Arduino Sensor Shield does what you are describing.  You can get them various places but here are a couple links for reference so you can see what I am talking about.
http://www.hobbyking.com/hobbyking/store/__26837__Arduino_Sensor_Shield_V5_0_Sensor_Expansion_Board.html

http://compare.ebay.com/like/120958516984?var=lv&ltyp=AllFixedPriceItemTypes&var=sbar

 


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