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Quick question: servo's, which ones and how they work? Answered

I am looking into making a stabilized gimbal for a quadcopter, so when it is correcting for wind, quick swings left and right, the level of parasitic tilting and panning from the rotors corrections is minimized. I have a mobius camera I am planning to design the gimbal for, and was wondering if it is possible to modify analog servo's to make them make fine and slow adjustments smoother?

So far, I understand the operation includes a geared motor that drives the output as well as a feedback potentiometer, and apparently the input signal is a 60 Hz PWM signal. My question is; is it possible to incorporate some sort of Phased Locked Loop that will lock onto the PWM signal's duty cycle and phase, and convert it to a higher overtone or harmonic (Such the case with a PPL used as a frequency synthesizer) and feed this into the analog servo, will it be able to make fine adjustments better?

Also, why is the servo signal output PWM only go from like 1% duty cycle to 10%? Why does it not utilize a broader range such as 1% to 99%? I would think that this would allow the signal to have better resolution and theoretically allow better, more precise control of said servo. Also, can anyone explain the operation of the servo and how it deals with the signal input, the feedback (which is a voltage value and not a PWM source)?

Surely digital servo's would be better, but so far I have only found them in larger versions, and considerably more $$$. What is a good source for micro digital servo's if those happen to be the best things to use? Would it be possible to make modifications to analog servo's to get rid of the jerkiness and jitteriness with minor corrections while still maintaining that level of correction? (AKA not increase the dead band, or if need be, remove it entirely however that is done.)

Discussions

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-max-

4 years ago

My multiwii controller has the ability to control servo's from it, and modify the Would it be possible the refresh rates from 50Hz to, say, 100Hz? Supposedly they can be upwards to 400, at least for digital ones.

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rickharris

4 years ago

As an addition none of the analogue servos I use in my aeroplanes suffer from jitter.

usually this is caused by poor or old potentiometers which are used to give position feedback.

You don't say where you are but Hobbyking sell a wide range of servo world wide in the UK Giant shark are one of the cheapest. Ebay is a valid source if you really wnt rock bottom pricing.

Technically a servo isn't necessary, a linear actuator is simple to build, or even uing a geared DC motor.

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-max-rickharris

Answer 4 years ago

I actually did consider using something other than a servo, especially considering there is already a feedback loop associated with an accelerometer a a feedback mechanism for the arduino to keep the camera's level. By jitter, I do not necessarily mean a tendency to vibrate but just non-smooth motion, because of the low refresh rate. Is it cheaper to just get geared motors similar to servo's standalone? I will need a H bridge motor driver to power them.

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rickharris-max-

Answer 4 years ago

Yes you will need an Hbridge not too hard or costly. look at the links i offered at leas 1 shows a bushless gimbel system

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-max-rickharris

Answer 4 years ago

I do not see any links in the comments, and the prices for a nice gimble are way over budget. I do not want to pay more than $20 for the system, I do not need to be able to control panning, I can have my quadcopter yaw in the air. I want to be able to control the level control in the tilting (up and down from the camera's perspective) externally as well as a feedback loop to keep it level with no user input, as well as stabilization (clockwise and counterclockwise) when the quad is accelerated to the left or right. It should be a simple and build for the small mobius camera.

Do you know if cheap micro servos can handle the weight of the mobius and mounting stuff out away <2 inches from the the shaft of them without support on the other end? or will that put too much stress on the bearings?