Infinite rotation servos

Kilby

Kilby

Active Member
Sorry for the off topic post, but I know someone here will be able to answer this question.

How do Infinite rotation servos work in relation to speed? With a traditional servo, if I move the stick 25%, the servo moves a something close to that. Do infinite rotations just adjust the speed according to how much stick you give it then since they don't stop the rotation?

I'm working on another photography project that isn't RC, but I see the need for a servo or small gear motor and I'm trying to figure out what to use. Thanks for the input!

-Terry
 


D

DennyR

Active Member
It really depends on weather the servo is modified for feedback or feed fwd. The servo only has one full speed regardless. but if it is working with the pot. locked then it's speed will be in proportion to the stick movement away from neutral, it will park in a new position as you return the stick to neutral, slowing down as the stick approaches that point. The more prof. gimbals tend to use this way.

With the servo modified for continuous rotation but with a pot. fitted to the axis of movement then it will respond like a normal servo over the span of movement that you have. This span is dictated by the pots gearing and its own internal ratio. This is not a great way to do it because the operator has to use sliders or knobs and is not conducive to good smooth mixing of 2 or 3 axis camera movements. The possible exception being on the roll as this is often set and then left. :tennis:

There is another way of doing things and that is to mimic the pot. by taking the voltage reference signal from the amp. board and modifying the the return signal to simulate the corrective movement. Also one can take the pot. and connect it to a mechanical stabilizer to achieve the same result.
 
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ChrisViperM

ChrisViperM

Active Member
DennyR said:
There is another way of doing things and that is to mimic the pot. by taking the voltage reference signal from the amp. board and modifying the the return signal to simulate the corrective movement. Also one can take the pot. and connect it to a mechanical stabilizer to achieve the same result.
Click to expand...

...whenever I feel happy and relaxed I stumble upon one of your posts...and the brain starts mumbling again :tennis:

Is there any chance to describe your statments in the quotes a bit more in a detailed and practical way....and how this could be used - I just guess it can be used - to force the servos who control the movement of a gimbal (not the compensation, the movement done by the camera operator) to a silky smooth movement. To me the real magic of Aerials is not the precise level of horizont or other "technical" gimmics, but to create the impression of zero-G like in a space shuttle, rather floating than flying. But so far I was not too lucky to archive this due to the rather aprupt movement (and stops) of the involved servos. If somebody can shed some light....I guess it has to be you :tennis:

PS: I guess this is something what kilby is behind as well....


Chris
 

J

jes1111

Active Member
Denny's first paragraph answers Kilby's question - in the "normal" way to 360-mod a servo you either disconnect the servo from the output shaft but leave it in the circuit (a "locked pot") or substitute it altogether with a pair of appropriately valued resistors. Such a servo will rotate at a speed proportional to the stick deflection.

The second para refers to the common way of utilising a servo on a geared gimbal axis - a multiturn pot giving greater span (rotation) of the servo.

The last paragraph, that Chris is querying, is effectively what the RSGS does - mimic a potentiometer with some stabilisation electronics. The output of the RSGS is identical to the output of a potentiometer - a variable voltage.

The smooth, "floaty" movement you're after suggests either an Ecilop-type machine or manual control of the gimbal (with or without some underlying stabilisation). On the other hand, wouldn't turning down the gain on a fully stabilised gimbal (i.e. deliberately allowing the gimbal to lag) be something close to what you want?

Just my €0.02-worth - Denny can now come back and clarify everything ;)
 

D

DennyR

Active Member
Well Chris, what I did was to describe the effect of servo response in respect of changes in PWM signal with a continuous rotation servo. In answer to Kilbys question.

The integration of stabilization is another story and can be achieved in more than one way.

The servo has disadvantages over synchronous direct drive motors when stabilizing a mass balanced axis. I doubt that you will ever see the ultimate floating rock solid locked-in effect from a servo driven gimbal unless it is mounted on an already rock steady airframe. Traditionally a mass balanced axis floats on a precision device and it naturally wants to stay in that position. The motors float that mass against any disturbed movement at high speed. In some cases they can even attenuate minor vibrations. That is never going to happen with a assynchonous motor driven servo because it has to drive a gear train and reference a feedback signal. essentially it cannot float. The Skyline makes an attempt to speed up the response with the pot v.ref solution. but as we have seen it creates more problems than it solves. As the IMU is mounted directly on the tilt (final) axis it cannot sense a movement until a movement happens.

This does not really tell you much accept that as we speak DJI are the only ones who have cracked it at an affordable price. Sorry if that is not what you wanted to hear but it's the only answer that I have. I can tell you how to build your own but it will cost far more and be much heavier.
 

ChrisViperM

ChrisViperM

Active Member
DennyR + jes1111 (jes1111 + DennyR) = genius...thanks guys

My "problem" is to get a stabilized gimbal (which needs fast servos or direct drive motors) to be controlled (tilt and pan) manually in a very smooooth way. With pan - I guess - it could be done somehow by "freezing" the pan servo (which is normally not stabilized and connected to a port on the receiver and controlled by a knob on the radio), but tilt is a comolete different story, since it is integrated in the stabilization process. If I am not wrong it should be possible with the new Radian....but it would help already to know how to slow down the pan servo, meaning if I turn my knob to get the servo to start the movement very slooowly and keep a slow pace. Normally everyone is trying to have his servos as fast as possible....I am looking for the exact opposite.

Chris
 

J

jes1111

Active Member
Do you have a CopterControl board, Chris? If not - the first batch of the new CC3D is coming up for sale "very soon" (visit forums.openpilot.org and keep a sharp eye on the News section). One of the developers (Cossacs) has been "breathing on" the camera stabilisation code recently (not in the "release" version of the software yet), adding low-pass filtering to the stick inputs (that's "smoothing" to you and me ;)) as well as all sorts of other "gimbal tuning" goodies. He's using the CC3D as a dedicated gimbal controller (with great success). The "stick sensitivity adjustment" you refer to is already in the release version of the software, by the way.
 


D

DennyR

Active Member
If I could just throw another spanner in the works, we talked about micro stepper drives and torque motors in the past that can drive a gimbal. The DJI uses a CUI AMT102 encoder (made in the US) so it's a proper torque motor. The more you look at the Zenmuse the more you realize what goes into making something like this. The CNC machining of every component is simply amazing.
Don't even think about trying to copy it. You could make a small fortune out of a very large one.


Good news about the CC3D all we need now is a driver for torque motors.

I am sworn to silence but a well known guy in the states is about to release something that is going to help a lot of guys out there who are already committed with a very popular system. If I were not so attached to the Zen this would be my only other choice.
 
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ChrisViperM

ChrisViperM

Active Member
jes1111 said:
Assuming you're in Austria (I recall you mentioning a move?) you need http://www.opstore.eu/
Click to expand...

Yeahh, I should have been gone already to Brazil, but will take a few weeks more. Hopefully it hits the store before I am gone....getting stuff into Brazil is a little "complicated" but not impossible.

Thanks for all the good info's...should send a bottle of wine to Portugal

Chris
 

J

jes1111

Active Member
DennyR said:
If I could just throw another spanner in the works, we talked about micro stepper drives and torque motors in the past that can drive a gimbal. The DJI uses a CUI AMT102 encoder (made in the US) so it's a proper torque motor. The more you look at the Zenmuse the more you realize what goes into making something like this. The CNC machining of every component is simply amazing.
Don't even think about trying to copy it. You could make a small fortune out of a very large one.


Good news about the CC3D all we need now is a driver for torque motors.

I am sworn to silence but a well known guy in the states is about to release something that is going to help a lot of guys out there who are already committed with a very popular system. If I were not so attached to the Zen this would be my only other choice.
Click to expand...
AMT102 - US$23.63 each at Digikey - not too bad :) - not sure what you mean by "so it's a proper torque motor" - the position encoder would work with any kind of motor. Thanks for the info, though. I've always found their quoted figure of "0.05º" to be interesting - an odd figure when you try to work backwards from it.

I'm working on (as in "it's already running") the OP firmware for driving servos with packetized serial - the code architecture in OP is so neat/powerful that's it's actually very simple.
 

J

jes1111

Active Member
I'm so jealous of you moving to Brazil - it's about the only place in the world I'd rather be than right where I am ;)

Sending wine to Portugal would be like shipping ice cubes to the Eskimos :) - we have some of the best in the world here already! (you'll be shocked how much they charge for Portuguese wines in Brazil, though)
 


J

jes1111

Active Member
Nice place - I'm aiming a bit further north, like the southern end of Bahia.

I'm not fussy with the wine here - just bring me a bottle of Planalto and put some ice in the glass ;)
 


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