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How do I put together a repeat motion control head for a camera?

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New ( offline )
Posts: 3
Posted: 2012-03-14 18:21 
I apologize if this is the wrong forum, seemed like the right one.

So basically what Im doing (i.e, trying to do) is find the right parts on building a motion control rig for filming a movie, and at the same time understand them. I'll give as much details as I can.

Im a noob yes but Ive been doing extensive research and Im still unclear about a lot of the general workings of a robotic rig.

What I need is a robotic/motorized motion control head for a camera that incorporates 3 things...

1.) 4 axis. It needs to slide along a track, rise up and down vertically, rotate left and right, and tilt forward and backwards.

2.) Most importantly it needs to be able to record the motions I give it and store them so it can repeat those motions at a later date. I realize Im going to be shelling out some cash for something like this.

3.) I really need the motion to be as smooth as possible. So that the movement is exactly the same and it has frame by frame accuracy. My use for this rig is visual effects purposes. I know a motion control rig can significantly reduce the need for expensive rendering hardware for creating artificial environments in a movie.

So far the best camera head/rig Ive come across only has 3 axis functionality, but can one of those also be modified to slide along a track too?
This one for example
http://www.ebay.com/itm/Proaim-Pan-Tilt-Motorized-Head-joystick-Bag-for-videography-photographer-movie-/280838502697?pt=LH_DefaultDomain_0&hash=item4163477929#ht_6626wt_1396

Ive read up on servo controllers and how they can be used for this very purpose but like I mentioned I dont understand a lot of the parts that go into these devices. Im very unversed in the field of robotics, so I figured my best bet would be to consult with professionals who could maybe point me in the right direction.

But thats about all I can think of. Thats what Im trying to do and really need some help with. So any advice is very much appreciated and I thank everybody for their time.


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Admin ( offline )
Posts: 3759
Posted: 2012-03-15 08:29 
The systems we offer are Pan/Tilt/Roll (no vertical motion or motion along a track). A "hobby servo" is essentially a motor which allows you to send position commands, often between 0 and 180 degrees (some can do more depending on the system). You will also see systems use normal DC gear motors (no position or velocity feedback, but the motion can be very smooth). Last, a DC motor with encoder counts the number of revolutions of a motor's shaft and as such can provide an idea of displacement (and can also do continuous rotation). Most pan/tilt systems use hobby servos because they can be moved to specific positions. The issue with hobby servos is that their accuracy is usually not very high (1-2 degrees or more).

We do not offer any track systems, but the two common varieties are:
1) Have the cart (plus camera rig) self-propelled: this is usually needed when the track is very long or complex, and has the advantage of being a self-contained unit (no long wires). If you make or buy such a rig, the motors will need encoders so you know the position of the cart on the track.
2) Have the cart connected to a timing belt which is then connected to a DC gear motor on the track; this is great for short distances.

If you want to record (or program) and play back the same routines, a servo-based system is easiest to create. To control servos, you need a "servo controller", a 4.8V to 6V power supply which can provide the needed current (battery pack or wall adapter), and ideally something to program it with (computer / laptop). If you have a mix of servo motors and DC gear motors with encoders, you'll need a variety of motor controllers and likely a central unit (microcontroller) to communicate with them all.

You could try a linear actuator with position feedback for the vertical motion, but the motion may not be as smooth as you'd like. The other foreseeable issue is that you want "frame by frame accuracy" - at 30 frames per second; this will almost be impossible.

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Coleman Benson

RobotShop inc.
Putting Robotics at your service!™
www.robotshop.com

Lynxmotion
Imagine it. Build it. Control it.™
http://www.Lynxmotion.com


New ( offline )
Posts: 3
Posted: 2012-03-15 12:29 
Quote:
You could try a linear actuator with position feedback for the vertical motion, but the motion may not be as smooth as you'd like.


So its not as simple as just rigging an additional platform to the main head and connecting a motor to lift it up and down?

Not trying to degrade your sales but what parts could you recommend for me parts that can do a more accurate job than hobby parts? Something more on a prosumer level. I really want something thats accurate and can store lots of movements.
Also Not to sound all greenhorn but I dont really know how to program so anything with prewritten functionality would be great.

I will be using the short distance track, thats what my shots will require.
I guess frame by frame accuracy is pushing it, what I need is just a stable system that can accurately record matching movements so they can be seamlessly composited later.

Last, what do you know about Feedback Potentiometers? I was told this device could return a motorized head back to its original position.

Are there any reference manuals that can guide me through the process of buying these different parts and assembling them? Probably not but just thought Id ask.

All in all I appreciate your help and feedback, thanks alot.


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Admin ( offline )
Posts: 3759
Posted: 2012-03-15 12:57 
 Post subject: Video recording rig
Quote:
Not trying to degrade your sales but what parts could you recommend for me parts that can do a more accurate job than hobby parts? Something more on a prosumer level. I really want something that's accurate and can store lots of movements.


The highest quality pan/tilt system we offer (which has been used to film movies etc) is the PT-2100. This is user controlled and cannot record and play back motion. The PT785-S is the next best thing and uses servos. The motion is quite fluid and the accuracy is not bad. The storage and playback part are separate.

Quote:
Also Not to sound all greenhorn but I don't really know how to program so anything with prewritten functionality would be great.


If you don't want to do any programming, use the 4-servo recorder / playback controller.

Quote:
I will be using the short distance track, that's what my shots will require. I guess frame by frame accuracy is pushing it, what I need is just a stable system that can accurately record matching movements so they can be seamlessly composited later.


Do a bit of testing - it should be pretty close.

Quote:
Last, what do you know about Feedback Potentiometers? I was told this device could return a motorized head back to its original position.


Servos use potentiometers to get their feedback. There is a mechanical slider inside which contacts a conductive material of variable thickness to give a different resistance value for each angle. The type of potentiometer and the quality of the materials will really help with accuracy.

Quote:
Are there any reference manuals that can guide me through the process of buying these different parts and assembling them? Probably not but just thought Id ask.


We receive quite a few inquiries about this type of system, but have not actively searched for automated video recording systems or instructions. Perhaps we'll take a look. For the moment, your best friend is Google.

_________________
Coleman Benson

RobotShop inc.
Putting Robotics at your service!™
www.robotshop.com

Lynxmotion
Imagine it. Build it. Control it.™
http://www.Lynxmotion.com


New ( offline )
Posts: 3
Posted: 2012-03-15 13:11 
Quote:
The PT785-S is the next best thing and uses servos. The motion is quite fluid and the accuracy is not bad. The storage and playback part are separate.


The PT785-S looks really nice. I checked it out before but forgot about it. 2 questions about that head...
1. Can it move fast and slow? as I'll be needing both speeds.
2. By any chance can a slider dolly be mounted to the small platform of that head and its motor also connected to the servo controller so all the parts have simultaneous motion with the 1 servo controller? That way I'll have 4 axis of movement that can be recorded and played back?

Final question, does the potentiometer in the servos return the head to its original position or would something else be needed for that?

thanks.


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Admin ( offline )
Posts: 3759
Posted: 2012-03-15 14:02 
Quote:
1. Can it move fast and slow? as I'll be needing both speeds.


The servo itself can rotate at up to 1.38 seconds per 60 degrees, but it is connected to a 4:1 gear down, which decreases the maximum speed by a factor for 4 to 5.52 seconds per 60 degrees, or 33.12 seconds per 360 degrees.

Quote:
2. By any chance can a slider dolly be mounted to the small platform of that head and its motor also connected to the servo controller so all the parts have simultaneous motion with the 1 servo controller? That way I'll have 4 axis of movement that can be recorded and played back?


The base can be mounted to a dolly, and the dolly can be controlled from the same controller. However, we don't sell such a dolly.

Quote:
3. Final question, does the potentiometer in the servos return the head to its original position or would something else be needed for that?


The positions (including centered) are absolute.

_________________
Coleman Benson

RobotShop inc.
Putting Robotics at your service!™
www.robotshop.com

Lynxmotion
Imagine it. Build it. Control it.™
http://www.Lynxmotion.com


 

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