How many SERVOS are possible with the ARDUINO?

Forum 2005-2010 (read only) Hardware Troubleshooting
1

Hi there!

I´m workin´ on a project with the Arduino...and i´ve to control, i mean, six servos should move at the same time when i press a key(over serial send via Processing)...My problem is that five servos seem to be the magic border. When i write the code for six servos, none of the servos move. And the problem is not the Bytesize of the Program, its only 61...somethin´.

So my Question is how many SERVOS can i put on the ARDUINO? At the moment the are plugged at 5V. Is that the problem? Or is more than 5 Servos impossible?

Perfect would be 11 Servos...

So i hope to find Answers

Thanks so far

sb

2

have you tested your script without the servos connected? Probably you've reached the maximum power level... how much mA do your servos need?

3

which arduino board are you using?

4

In theory 12 but that would not be very effective, 9 is a more realistic number to get them to move smoothly, they need to be updated every 18ms, the pwm mark space is between .5ms and 2.5ms, center position being 1.5ms, so if we say the upper setting will be 2ms it's 18 / 2 = 9 servos, to get full swing 7 servos, i think this is how it's worked out, i've certainly had 7 servo's running on a pic before

5

Are you signaling all of the servos from one pin or do they all have a dedicated signaling pin?

6

I run 12 Servos on a standard Arduino without problem, but they do need a separate power supply.

How are you connecting and powering the servos?

I posted a simple servo test sketch in this thread: http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1268620031/3#3

You can use that sketch to command an individual servo or all servos.

7

9 is a more realistic number to get them to move smoothly, they need to be updated every 18ms

P18F4550, what is the basis for that statement?
I would be surprised if you could see any difference in movement between running 9 or 12 servos.

It is true that the servos may have a little less torque in the unlikely event that all 12 are being driven with 2ms pulses, but I have not seen any loss of smoothness of movement when 12 servos are driven.
have you?

8

mem,
i mean in movement, if they are stationary no there is no difference but if they are not updated every 18ms they get jittery, really it depends on the users individual code

9

if they are not updated every 18ms they get jittery

That's not been my experience.

You can test this by changing the servo library so that all servos have a refresh period of 24 milliseconds and see if you can detect any more jitter or change in performance with the servos.

To do this, change the following constant in Servo.h to 24000
#define REFRESH_INTERVAL 20000

I would be interested to hear if you can detect a significant difference.