Servo spec question

[cjm180]

Hi

if a servo has a centre pulse of 1520us, how do you determine the pulse at the servo extremes?

likewise if a servo is 760us

thanks

[waveydavey]

Referred to this article a number of times and it gets complicated if you're not a thinker, I'm not a thinker

https://www.helifreak.com/showthread.php?t=263175

[Mike656]

Endpoints could be 1000 or 2000us for the 1520 servo. Increasing or decreasing the spread adjusts the servo travel. 760us allows twice the number of pulses, so should give finer control.

[nkma]

Hi

if a servo has a centre pulse of 1520us, how do you determine the pulse at the servo extremes?

likewise if a servo is 760us

thanks

Here they say a Hitec servo operates on a pulse with a width of 0.9 ms to 2.1 ms and centers with a 1.5 ms pulse.
Servos | HITEC RCD USA

Here they say the pulse width should be between 1.0 ms and 2.0 ms.
https://os.mbed.com/users/4180_1/not...ion-to-servos/

The whole range could correspond to 180°, but it could be less or more.

Servos that center at 760 µs (or 750 µs) typically accepts 510-1010 µs (or 500-1000 µs).

The exact answer to your question can vary.
The output travel could be 180° and give you 1.8°/10µs for a 1.5 ms servo and 1.8°/5 µs for a 760µs servo, but that varies too.

This information, like max frequency, should be part of every servo spec, but it isn't.

/Bo

[cjm180]

Thanks for the responses.

I went away and read the helifreak post. All good stuff and certainly clearer. So what i have is some second hand servos and i thought it would be a good idea to put them on my servo tester that i dont get to use often. The tester is integral to my 406duo charger. What does the 45deg pulse traveling mean?

so 1520us, 333hz cyclic servos...



This is powering the servo directly from a 2s lipo, it shows a speed of 0.044s/60deg. The specs quote 0.079s. so is that normal??

Also, in the fixed end point test, it will only let me set the bottom at 1320us and the top at 1720us. Why is this??





The tail servo, 760us at 560hz...



it says 0.128s / 60 deg. the specs say 0.036 at 7.4v.

The servos are going into a goblin 700, so while i have seen them working on the bench and nothing is making me think something is wrong, i just wanted to understand the test and rather than looking for something that says they are bad, look for something that says they are good! if that makes sense

[cjm180]

Had a bit of a play around with things tonight....

opening up the 45 degree pulse traveling setting seems to give you further scope in the linear test range. So what i did was i kept moving the linear test angle until the servo stopped responding and then came back 10us.

this has given me the pulse at top and bottom. it also gave me the angle (roughly eyed it up at the limits) and i think its at 120 degrees as said. Note here the 120 degree movement did not tie up to the angle reading on the linear test!

So for the 1520us servo, i have the lower pulse at 780us, and the upper at 2160us.

So over 120 degrees, the pulse changes by:

2160 - 780 = 1380 difference

1380 / 120 = 11.5us change in pulse for 1 degree of movement.

45 * 11.5 = 517.5us change in pulse for 45 degrees.

i then set the 45 degree pulse travel to 517.5us and went back to the linear test. No the angle on screen ties up really close to the actual servo (checking it at 90 degree movement).


Similarly for the 760us servo, i got 390us min and 1080us max at 120 degrees.

1080 - 390 = 690

690 / 120 = 5.75us change per degree (exactly half of the 1520 servo!!!!)

5.75 * 45 = 258.75us change per 45 degree.

Again i set the 45 degree angle travel to 259 and the angles onscreen work out to what the servo is doing. I then ran the speed test again and at 7.2v its covering 60 degrees in 0.052s.

I have emailed the servo manufacturer to ask what the min and max pulse is, and what the pulse is at 45 degrees. Hopefully they will come back and the answers will be similar to mine.

Kr
Craig