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Topic: Arduino Mega with 8 servos - simple circuit question (Read 890 times) previous topic - next topic

flick

Hi, I am trying to control 8 servos (HS311 standard analog) using an Arduino board. I would greatly appreciate if someone can help with these questions:

1. What is the simplest/cheapest Arduino board I need to complete this task? Should I go with the Mega?

2. If I run all 8 servos at 6V, do I need any additional hardware? External power source?

3. I found this tutorial to interface a servo with the Arduino board. I am not clear on how to set voltage to 6V. Suggestions?
    http://arduino.cc/playground/Learning/SingleServoExample

Thanks.

virtualmix

#1
Dec 05, 2011, 01:38 am Last Edit: Dec 05, 2011, 01:41 am by virtualmix Reason: 1
Hello flick,

Controlling servos with Arduino is pretty easy since a "servos library" is included in Arduino. Here is a good examples to start with.
Using this servo library, you can control up to 8 servos. If you ever want to control more than 8 servos, you will have to use a separate servo controller. (Pololu and Lynxmotion provide nice servo controllers).

All servos can be powered from 4.8 Volt to 6 Volt. The higher the voltage the more torque on the output shaft. The voltage vs. torque values should be given in the servo datasheet so you can have an idea on what to expect.

So, to answer your questions:

1) Any Arduino board will do the job. You need 1 analog output pin per servo, so 8 analog output pins to control 8 servos. The Arduino Uno and the Arduino Nano have 12 analog output pins each and the Arduino Mega has a lot more.
You can get a very cheap Arduino Nano clone "made in china" on Ebay (~10€). Note that when you by a clone, no money goes to the official Arduino project :-(

2) You can run them all at 5V from the board to avoid using an external power source. Try to find how much current you need to power 8 servos (each servos are different have a look at the datasheet) and if you ever have to use an external power source, just connect it to the red wire on the servos. (or maybe you can use the VIN pin, I'm not sure)

3) In that example, the servo is powered at 5V from the Arduino. No need for voltage regulation here.

Hope this help.

zoomkat

Quote
You can run them all at 5V from the board to avoid using an external power source.


Totally bad answer. You will need an external power source to power he servos.
Google forum search: Use Google Advanced Search and use Http://forum.arduino.cc/index in the "site or domain:" box.

flick

Thank you both for the responses. I checked the
HS311servo details and got the following running at 6v:

Idle current 7.7ma
Running current 180ma
Stall current 800ma

I'll go ahead and order a Mega in case I need additional functionality. I have a universal adapter (converts 120v to 6v/300ma) but not sure if that is what I would need as the external power source. I dont want to use batteries. I will try it out and will get back with any questions if I run into issues. Thanks again.


retrolefty

#4
Dec 05, 2011, 06:47 am Last Edit: Dec 05, 2011, 06:49 am by retrolefty Reason: 1
Quote
I'll go ahead and order a Mega in case I need additional functionality. I have a universal adapter (converts 120v to 6v/300ma) but not sure if that is what I would need as the external power source. I dont want to use batteries. I will try it out and will get back with any questions if I run into issues. Thanks again.


300ma will not be near enough to run your 8 servos. Actual current requirements will depend on what mechanical load you place on the servos, how far you command them to turn, how many are commanded to be turning at the same time, etc, etc. I would want a 5 amp 5vdc power source for 8 servos, minimum, 7 amps would make me feel comfortable. That would support 8 servos all at stall condition at the same time, or otherwise called worst case condition.


Lefty

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