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Topic: Round video image to pan/tilt module (Read 118 times) previous topic - next topic

Carlowww

Hi,

I'm starting a new project, but I'm not really sure which products I will need. Maybe someone could help me with it, I've googled to much..

The plan:
I'll get coordinates from a videofeed and with those coordinates a camera will be pointed onto that direction accordingly. The camera will be aimed at the right coordinates with a pan-tilt module. On the pan-tilt module will be around 200 to 400 grams of weight. When the camera is aimed at that right direction, it will track an object and send new coordinates to the pan-tilt module to keep tracking it. 

Minimum requirements:
The pan motor needs to be able to spin at least 360 degrees.
The tilt motor  needs to be able to spin at least 100 degrees.
Turn 200 to 400 grams of weights
Relative fast turning

The questions:
  • (Which) Servo's or Steppers? Steppers can give feedback about their current position right?
  • What kind of pan-tilt bracket will be suitable? Or where can I find information about this?
  • Do I need a Motor board controller/driver for servo's/steppers?
  • Do I need extra external power for the motors?
  • Am I missing something?


I would really like to hear your thoughts!

MorganS

1. Steppers cannot give feedback but, if you have a known starting position such a a "home switch" that's hit by the carriage, then you can just keep count of steps done. Since the coordinates come from the camera, you only need relative positioning, don't you?

2. A block of wood is good to start with. There's also lots of gimbal brackets available from quadcopters and camera stabilisers. A nice gimbal without motors or electronics might be $20-$50.

3. Yes.

4. Yes.

5. I'm not clear on what kind of camera or how you're extracting coordinates from the video but if you think you have that part sorted out already, I'm inclined to believe you.
GoForSmoke: "What GShield? You never mentioned a shield."

Robin2

You may find something useful in these links
Stepper Motor Basics
Simple Stepper Code

If servos are suitable they will be much easier to work with, mechanically, electrically and from a programming point of view. Sail Winch servos can turn about 3 revolutions with position control.

If you design a gimbal so that the rotation takes place at the camera's centre of gravity the loads on the motors will be lowest (or use a counter-weight to balance the system).

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

Can you say something less vague than "Relativel fast turning"?
Can you also put some sort of figure on the angular accuracy and smoothness required.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Carlowww

1. Steppers cannot give feedback but, if you have a known starting position such a a "home switch" that's hit by the carriage, then you can just keep count of steps done. Since the coordinates come from the camera, you only need relative positioning, don't you?

2. A block of wood is good to start with. There's also lots of gimbal brackets available from quadcopters and camera stabilisers. A nice gimbal without motors or electronics might be $20-$50.

3. Yes.

4. Yes.

5. I'm not clear on what kind of camera or how you're extracting coordinates from the video but if you think you have that part sorted out already, I'm inclined to believe you.
Thank you! I would love to have absolute positioning, but I don't know what's simpler.
What I'm inclined to do: 2 cameras, one 360 dome camera which views at the whole area. Once a bird comes into view, the coordinates of the bird will be passed to the servos which have a secondary camera (with a better image). Once the secondary camera has the bird in center, those (relative) coordinates will be send to the servos.

You may find something useful in these links
Stepper Motor Basics
Simple Stepper Code

If servos are suitable they will be much easier to work with, mechanically, electrically and from a programming point of view. Sail Winch servos can turn about 3 revolutions with position control.

If you design a gimbal so that the rotation takes place at the camera's centre of gravity the loads on the motors will be lowest (or use a counter-weight to balance the system).

...R

Thank you! With my answer above, do you think that servos are more suitable?

Can you say something less vague than "Relativel fast turning"?
Can you also put some sort of figure on the angular accuracy and smoothness required.

You're right! With a flying bird and a camera, some accuracy an smoothness is required. Since bird can fly pretty fast, the turning has to be react fast. But with some distance between the camera and the  bird, it doesn't have to be That fast.. What are your thoughts?

MorganS

Servos will not achieve the required smoothness. The steps they take are too large.

Steppers will also have a problem with a smooth pan. You may be able to gear them down and use microstepping but then the gear train adds backlash and instability.

Brushless gimbal motors may do what you want but I've never seen them used in this kind of tracking application.

A lot of this depends on the zoom level you want. What field of view or equivalent focal length are you planning for the secondary camera? If your FOV is 40 degrees (50mm equivalent) then you could use servos by not attempting to track the bird precisely - let it go a long way to the edge of the frame before swinging to follow it. During the swing, the image will be shaky and horrible.

A Kodak Pixpro SP360 is able to record a complete hemisphere and you can then 'zoom in' to produce a 1080P section of that after the recording is made. I've done this to track another airplane from the Kodak stuck on the bottom of my own plane.
GoForSmoke: "What GShield? You never mentioned a shield."

Robin2

Thank you! With my answer above, do you think that servos are more suitable?

What are your thoughts?
I think you need to do some practical experiments.

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

MarkT

Sounds like you have a finder camera and a telescope (in effect), so you are looking
for something akin to astronomical telescope mount, but lighter and faster.

I think you are going to need encoder gearmotors (ie servomotors in effect), though
gimbal motors fed-back from an IMU might be accurate enough (and easier to get all
in one package).

I suspect the sort of set up for semiprofessional drone filming might be a place to look
for a complete system - but look out for the issue of accuracy, IMUs have significant
drift and inaccuracy compared to encoders - no problem for locking on to the target,
but open-loop control for initially aiming the camera is going to be subject to all those
errors.

You may also be able to add encoders to a gimbal system. 
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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