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Join Date: Sep 2016
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Stabilized Arm That Holds a Camera Steady

09/04/2016 12:58 AM

I'm building a stabilized arm that holds a camera steady in the up and down directions on something like a big quad bike.

So far I have a test mass of 140kg on a 1.2m arm held level by a suitable spring linkage that supports the mass ~ weightlessly over its range of +/- 45deg and an 800W brushless motor turning a ballscrew that applies a force to raise and lower the arm.

Ballscrew pitch is such that without drive to the motor the reflected inertia of the shaft/motor has only a small effect and the arm floats along quite smoothly over minor bumps.

I have an 400Hz update IMU which outputs the angle of the arm and its vertical acceleration, mounted near the arm's pivot. A microcontroller reads the arm angle from the IMU and compares it to the previous arm angle and derives a drive torque value sent to the motor. There is a derivative term based on the change in rate that can be applied.

Also I measure vertical acceleration (- gravity) and use it to modulate torque as a way to reduce the load on the motor on big bumps as the arm tries to stay still and the vehicle rises and falls.

While it works reasonably well I feel there is a better control strategy and wonder if anyone would care to make a suggestion.

Thankyou for your consideration

SBH

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Pathfinder Tags: control theory PID stabilization
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#1

Re: SBH

09/04/2016 1:42 AM
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#2

Re: SBH

09/04/2016 2:39 AM
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Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
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#3
In reply to #2

Re: SBH

09/04/2016 5:35 AM

Greetings,

The cameras are mostly Arri Minis these days, the usual sort for filming TVCs etc and mounted in an already built stabilizing head that allows pan tilt and roll by remote control.

Camera and head weight ~40kg.

The question is more about the particular control methodology given the large inertia and vertical acceleration disturbance. It works with modified PD control but there might be a better way.

Regards,

SBH

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#5
In reply to #3

Re: SBH

09/04/2016 1:12 PM

Well it seems to me the basics of stabilization would include a 3-axis gimbal with gyroscopic stabilization...40kg is a challenge...

So you have something like this already?

http://nofilmschool.com/2015/02/arri-alexa-mini-smaller-package-price-cost-release-date

New Alexa mini...

http://freeflysystems.com/movi/m15

http://www.quadrocopter.com/Freefly-CineStar_ep_63-1.html

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#6
In reply to #5

Re: SBH

09/04/2016 2:03 PM
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#8
In reply to #6

Re: SBH

09/04/2016 2:28 PM

Unit: Intuitive Aerial - Aerigon

Camera: RED, FS7 up to 8kg

Flying time: 8-10 min

Total weight: 25 kg

http://whiteoutpictures.com/gear/heavy-lift-drone/

over 30 kgs....airlift

http://www.riseabove.com.au/products/vulcan-cinematographer-heavy-lift-octocopter-complete-aerial-package.html

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#4

Re: SBH

09/04/2016 10:56 AM

It is difficult to make suggestions, since you don't really say how you want the arm to perform. Do you want the final result to look rock steady, or do you want a fluid motion with gentle amounts of accelerations? Do you want no trace of vibration or shakiness, or do you want a pseudo hand-held effect?

If you have a specific effect in mind, or perhaps the option to dial-in different effects, perhaps you need computer control that can remember the mtion along the chosen track, and has the ability to add or subtract motion to the remembered path.

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#7

Re: SBH

09/04/2016 2:14 PM
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#9
In reply to #7

Re: SBH

09/04/2016 10:51 PM

Yes, it is like the top one which probably has a passive spring damper system, perhaps with MR control but I want a longer arm hence the 140kg load for testing.

I want to be able to apply keep the mass more restrained on big bumps and perhaps the ballscrew is not allowing the decoupling of the mass from the vehicle frame allowing feedback as the as the error term gain is increased.

I'm thinking of trying mechanical low pass filtering between the ballscrew and the arm, some sort of spring isolator, next.

Regards,

SBH

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#10
In reply to #9

Re: SBH

09/05/2016 12:24 AM

What about some high travel suspension parts ...just spitballin'

http://www.metalcloak.com/JK-Wrangler-3-5-OME-Duroflex-Suspension-System-p/7118.htm

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#11
In reply to #9

Re: SBH

09/05/2016 3:45 PM

Bottom one I mean

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#12
In reply to #11

Re: SBH

09/05/2016 4:50 PM

It seems to me that 2 layers of suspension would suffice....first the vehicle platform itself...rock climber or Baha type high travel suspension with the same setup tuned for the arm....add to that the multi axis and gyro stabilizer assembly, and I guess that's as good as it gets, , without going airborne...

http://www.eng-tips.com/faqs.cfm?fid=768

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#13

Re: Stabilized Arm That Holds a Camera Steady

09/19/2016 10:52 AM

One radical concept would be to use a vertical Lorenz motor principle: with this drive, a physical position change of the 'stator' (on carrier vehicle) does Not translate directly to the 'rotor' at all: this drive is force-based only. It is completely up to the motion control algorithm to keep the 'rotor' in the desired position. However, for a true Lorenz drive, stroke lengths are usually pretty limited so this setup will probably be most effective as a high frequency vibration damper.

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