Continuous Rotation Servo Question
chaosgk
Posts: 322
Can someone tell me a little more about the continuous rotation servo from parallax.·
A project I will be working on in the near future (when my CNC and relay board is done) is going to be a RC Predator UAV with aerial photography.·
I already have experience with building and flying RC aircraft and using servos and all of that. What I want to do is build a mount for the onboard cameras, the idea is to have a pod in the front that is self contained with the cameras and battery pack. I want the pod to be able to track the same spot no matter what position is in the sky. I'm thinking of using heading hold gyros to control the two servo's for the X and Y axis of the camera mount with the continuous rotation servos connected to them.· This should allow the camera to rotate 360 degrees and hopefully 180 degrees for the Y axis.· How exactly do the continuous rotation servo's work. I know on regular servo's, the pot tells the control board where it is and where zero is.· Is this the same for the continuous ones.· I have a 9 channel transmitter and I figure it is going to take 5 channels for the camera system alone,
(not the channels used, just a list of what I picture)
1. X axis rotation
2. X axis gyro enable
3. Y axis rotation
4. Y axis gyro enable
5. Snap picture.
I'd like to be able to use knobs or sliders on the radio to aim the camera at an object or location, then flip on the gyro switches and have the heading hold lock the camera in place.· Using heading hold gyro's, they should be able to sense the changes in pitch and roll and compensate for minor changes in direction.
What do you all think?
·
A project I will be working on in the near future (when my CNC and relay board is done) is going to be a RC Predator UAV with aerial photography.·
I already have experience with building and flying RC aircraft and using servos and all of that. What I want to do is build a mount for the onboard cameras, the idea is to have a pod in the front that is self contained with the cameras and battery pack. I want the pod to be able to track the same spot no matter what position is in the sky. I'm thinking of using heading hold gyros to control the two servo's for the X and Y axis of the camera mount with the continuous rotation servos connected to them.· This should allow the camera to rotate 360 degrees and hopefully 180 degrees for the Y axis.· How exactly do the continuous rotation servo's work. I know on regular servo's, the pot tells the control board where it is and where zero is.· Is this the same for the continuous ones.· I have a 9 channel transmitter and I figure it is going to take 5 channels for the camera system alone,
(not the channels used, just a list of what I picture)
1. X axis rotation
2. X axis gyro enable
3. Y axis rotation
4. Y axis gyro enable
5. Snap picture.
I'd like to be able to use knobs or sliders on the radio to aim the camera at an object or location, then flip on the gyro switches and have the heading hold lock the camera in place.· Using heading hold gyro's, they should be able to sense the changes in pitch and roll and compensate for minor changes in direction.
What do you all think?
·
Comments
A continuous rotation servo is like a motor, it has no reference to any point in it's rotation. It can not be used in the manner of which you want. They basically take a servo, and disconnect it feedback pot. This causes the servo to "hunt" it position it is attempting to reach. This is what makes it continue to turn.
What you are looking for is a >90 degree rotation servo. I think Servo City has them, but you would need to browse around there. There are other servos (not R/C) which are capable of doing this. Dynamixel is one manufacturer of a servo which will serve the purpose you are attempting.
I hope this helps.
James L
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James L
Partner/Designer
Lil Brother SMT Assembly Services
The other question, how does a servo know which direction to move, is it based on pulses, with a heading hold gyro attached, wouldn't it be sendin out pulses constantly telling it what direction to move, if a servo gets the pulse that says stay in one spot, wouldn't it stay where it is until the gyro says to move one direction or another?
Yes servos use a frequency bandwidth to know where they need to go. If you need them to go left the frequency goes up, right and it goes down. It is a little more complicated than that, but the basis is simple.
Well you have the basic idea about the movement.
Basically the "on" time of the frequency tells the servo where to go. If the on time is 1ms the servo will go to 0 deg. If it is 2ms it will go to maximum (90,100,140, etc). If the pulse on is 1.5 ms it will center. You tell the servo where to go, by adjusting the "on" time of the frequency.
This makes it easy, for the receiver of a RC plane doesn't have to keep telling the servo to move a little. It just tells the servo where to move, and the servo goes to that point. If the position needs to be changed, the receiver tells the servo the new location.
I think this will explain enough of how it works.
James L
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James L
Partner/Designer
Lil Brother SMT Assembly Services
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.
Plus the UAV itself still needs to get drawn up and built, but of all of my current hobbies, making something built from scratch fly seems like one of the easier ones. I made a combat plane last year out of some scrap rain gutter downspout, pink foam for a wing core with carbon fiber arrows for support and balsa sheets for the tail secition. I love that plane, cause there's really nothing in it, it flies great and is designed specifically to crash so if it does, we just laugh and I replace a part and put it in the sky again.
Sounds like a real cool project.
I was working on one a year or two ago, but dropped the project. The complexity of the project got to be enormous, so I decided to put it on the "way out back, down south back burner". The project was way more than a simple RC to UAV type project, and probably so much over my head I couldn't justify it.
With all the Kalman filters being written, it may get started back up after the two projects I'm working on. It will be a minimum of a year before they are done and totally debugged though.
Just for giggles, you may want to use a linear servo for the tilt. Here is an address of one I've been watching for a long time. One version does use the pulse method of control. http://www.firgelli.com/
They are pricey, but really cool.
James L
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
James L
Partner/Designer
Lil Brother SMT Assembly Services
We didn't have any rain for the last half of the summer of 08 so every place we hunt was too dry to even use it so it hasn't even been out yet.
I'll do some posts when I start the UAV project but I need to light up the sky first unless my A.D.D kicks in one night and I decide to start drawing up some plans. I would like to have it functional by the end of August for our club funfly.