external power to adafruit 16 ch servo driver

[adafruit_support_bill]

Please see my earlier post:

Most servos will work with a 50-60Hz period and a pulse width between 1 and 2 milliseconds.

This is the industry standard spec for RC servos.

[klemenz]

OK I use following:

Code: Select all

		// pwm.setPWMFreq(1000)
		float freq = 50;
		int prescaleval = 25200000; // 25MHz
		prescaleval /= 4096; // 12-bit
		prescaleval /= freq;
		prescaleval -= 1;
		Log.d(TAG, "Setting PWM frequency to " + freq + " Hz");
		Log.d(TAG, "Estimated pre-scale: " + prescaleval);
		int prescale = (int) Math.floor(prescaleval + 0.5);

and

	final int servo_min = 170;
	final int servo_max = 390;

I checked the osciloscope - the delay from one signal to another is exactly 20ms, the pulse length with servo_min is exactly 1ms, pulse length with servo_max is exactly 2ms as it is stated on http://learn.adafruit.com/adafruit-ardu ... rvo-motors, but angle is les than 180 degrees.

Have you made some tests with this servo? What have you found?

[BeerCannon]

Servos don't necessarily traverse an entire 180-degree arc. They traverse "about" 180 degrees.. usually a bit less, from the ones I've used (Parallax, Tower).

[klemenz]

OK I respect that answer - but shouldn't that be somewhere documented?

ADAFRUIT:
The best web page to put this information on is in http://www.adafruit.com/products/1143

Data I am missing:
frequency in MHz
angle range in degrees

For sure it would say me a lot of hours of hit and miss retries...

[klemenz]

Actually in that page it says it should move in 180 degree range... So what is the correct information now? That information is for sure somehow misleading...

[klemenz]

Here is also pictures from osciloscope so you can see period is 20ms, and pulse length is 1ms, 1.5ms and 2ms.

Can somebody from adafruit give correct answers regarding angle degrees and please not general answers but answer for THIS PRODUCT - Tower Pro MG995R - or I expect somebody will correct product page http://www.adafruit.com/products/1143.

Best regards,
klemenz

[adafruit_support_bill]

Can somebody from adafruit give correct answers regarding angle degrees and please not general answers but answer for THIS PRODUCT - Tower Pro MG995R - or I expect somebody will correct product page http://www.adafruit.com/products/1143.

As I have explained in previous posts, these are analog circuits and there is variability from one sample to the next. The industry standard timing for RC servos is a 50-60Hz period and a pulse width between 1ms and 2ms. These will get you in the ballpark. For precise positioning, you need to calibrate this for each servo. That is why RC transmitters all have "trim" adjustments.

If there is a mechanical issue that physically prevents your servo from moving the full 180 degrees, then we will replace it. If a 1ms-2ms pulse range at 50-60Hz does not give you something close to a 180 degree swing (+/- 10 degrees) then your servo has a defective circuit board and we will replace it.

If either of these is the case, please contact [email protected] with a link to this thread and we can arrange a replacement for you.

[adafruit_support_mike]

or I expect somebody will correct product page

From the product page:


Note the word "approximately".

These are not precision positioning devices. We do not sell them as precision positioning devices, and we do not promise they will behave as precision positioning devices.

[klemenz]

Well I am missing 45 degrees here. I don't know definition of appropriately but I assume that should be not more than maximum 5 degrees.
Could somebody in adafruit make some test with exactly this servomotor - so it could maybe spare me sending servomotor "Tower Pro MG995R" back to adafruit.

You can check video at https://plus.google.com/photos/11023068 ... banner=pwa

[adafruit_support_bill]

The MG995R samples I have here both have a range of motion of just over 200 degrees between physical stops (rotating by hand).
Giving both the same 1ms to 2ms signal, one sweeps over a range of 168 degrees and the other 173. Both can cover the 180 degree range by adjusting the timing on the high and low limits.

Please contact [email protected] with a link to this thread and ask for a replacement.