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servo current
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Please be positive and constructive with your questions and comments.

servo current

by Selaseth on Mon May 05, 2008 6:10 pm

Hi

My question concerns the remark about connecting a motor to two ports at once. I am asuming this counts for servos also?

I am using a SPG800A power servo from servocity. This servo pulls 700mA on "no load" with 4.5 or 6V according to the Hitec spec sheet.

Am I supposed to connect the two servo ports in parallel to the servo? Do I also have to "activate" the other servo via Arduino code (servo2.attach(10))so that current flows?

And am I right to guess that the USB port will not suffice in current thus needing a stronger external 6V transformer?

-Eddi
Switzerland
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by franklin97355 on Mon May 05, 2008 6:44 pm

The servo signal is TTL level and not much current. The power to the servo can be directly from the power source (regulated) You must tie the grounds together.

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by Selaseth on Mon May 05, 2008 6:50 pm

Ok, I'll try with a external 6V 700mA+ transformer with the two minus pols tied together on the shield.
Thanks!
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by Selaseth on Tue May 06, 2008 4:21 pm

Other question: Is it possible to attach for example a 4 ampere servo/stepper through several arduino + motor shields to "share" the current?
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by Selaseth on Tue May 06, 2008 6:05 pm

franklin97355 wrote:You must tie the grounds together.

I don't get it, the two grounds are already tied together on the curcuit board for the servos..
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by adafruit on Tue May 06, 2008 8:20 pm

tie the ground from the 6V high-current supply to the arduino's ground

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by Selaseth on Wed May 07, 2008 7:14 pm

Can you perhaps quickly check if I did it right?
I connected the 5V Pin (red wire) from Arduino to the "+" Pin of the servo

[img=http://img440.imageshack.us/img440/6929/img2026iu0.th.jpg]
[img=http://img185.imageshack.us/img185/7230/img2024iw1.th.jpg]
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by adafruit on Wed May 07, 2008 9:25 pm

umm, thats not what you want according to what you said
you should connect the high power supply -only- to the servo's + pin and NOT to the arduino
power the arduino from the wall adapter or USB as normal

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by Volt Dropper on Thu May 08, 2008 11:50 am

OP That servo should have come with a splitter. The splitter is used to allow for external power for the servo...

In other words, On a typical RC plane the servos draw current thru the radio. (Like you're trying to do with the Arduino) But when you get to the big guys you'll fry your radio. (or Arduino)

So the splitter goes like this....


External 6V source -----\
Battery --- Radio --------*==== servo

The power pin only goes to the external source. So one battery operates the radio and small servos and the big servo has its own source. (but gets the signal from the radio)

DO NOT try to draw that much power thru your Arduino. That servo is a monster.

If you lost/threw away the splitter, Servo City has replacements.

(BTW have that same servo on the front of my kids ride in train.... (regular servo not the gearbox) it's been very durable if a bit noisy.)
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by Selaseth on Thu May 08, 2008 1:21 pm

Hey thanks, I was wondering what that cable (splitter) was for. I'll try that out!
Yes, I was worried, it would fry my arduino as the servocity guy said i would at least need 3 amps ;)
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by Volt Dropper on Fri May 09, 2008 12:27 am

Selaseth wrote:Hey thanks, I was wondering what that cable (splitter) was for. I'll try that out!
Yes, I was worried, it would fry my arduino as the servocity guy said i would at least need 3 amps ;)


Hey, glad it helped.

BTW I don't know what you're using it for, but my local Academy Sports has 6V SLA batteries cheap. With looooong Ah ratings. If you're pulling that much current, I'd look at that over NiHM packs. (assuming you have the space and can handle the weight etc)
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by Selaseth on Fri May 09, 2008 7:46 am

I'm using it for a sound installation to wind up cable to open a lever to let sand out of a 3m hourglass..lots of force required.
Btw, my splitter is such that it looks more like its for attaching two servos on one port instead of being able to attach an external power source.. What I'll do as soon as i get my 6V / 20ams transformator is to attach it directly to the servo via the +/- pins and attach the signal cable to the signal pin on the arduino.
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Please be positive and constructive with your questions and comments.