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Anti-vibration tables and mounts.

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LAN_403

Patrick

Fri Jul 04 2014, 11:25PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

with all of these new flying and ground bots, some are starting to run into vibration problems creeping into there vison and laser based systems. I know there are industrial solutions for wafer and astronomy situations, but their stuff looks like it weighs 50 to 10,000 lbs and it all looks super expensive.

do any others here on the forum have experience in this matter?

how do these work? i presume theres a reason they weigh so much. do they have really large piezo discs? or many thin in series? for a common vibration (i know thats a vague defination) is there alot of linear movement needed?

its mostly video and laser "bouncy-ness" and microphony, were trying to minimize.

Andy

Sat Jul 05 2014, 04:01AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
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Posts: 874

HI Patrick
Can't you do the correction in software?, wouldn't a group of pixels that are the same RGB that move left or right beable to be auto corrected?

Patrick

Sat Jul 05 2014, 07:12AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Yes, but...
Im always suspicious of software, especially in applications that correct hardware which should have been designed right the first time.

Carbon_Rod

Sat Jul 05 2014, 09:28AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
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Posts: 1155

This problem goes back to the time of equipment isolation in aircraft.
Vibration damage can actually pop SOICs off their pads if incorrectly bonded.

Image stabilization is usually done with motion controller gimbals and gyro.

With rotor craft most vibration is caused by an unbalanced set of blades.

Patrick

Sun Jul 06 2014, 08:38AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Carbon_Rod wrote ...

With rotor craft most vibration is caused by an unbalanced set of blades.

but what if i have a single piston revolving at 8k rpm? i dont know how good or bad that situation will be...?

...

Sun Jul 06 2014, 03:53PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Commercial vibration isolation systems (like for optics or whatnot) are heavy because they are a simple analog of a low pass filter, where the tabletop represents a capacitance, and the heavier it is the further you can push the pole down. With a nice thousand pound block of granite on top of a pneumatic isolator of some sort (designed to act like a constant current source, or large value inductor with dampening resistor) you can get decent attenuation down into the sub-hertz level which is sufficient to block out most sources of vibration, or at least let your feedback loops take out anything which is still there.

Clearly that approach is not going to work on a drone, although you could probably find a way to make a hybrid active/passive system which consists of a fast gimbal to take out the craft movement, and a piece of squishy rubber (you want something which has a lot of friction internally, to dissipate the energy, otherwise you are just building a resonator) to attach it to the craft. In order to really get good quality pictures you may need to look into some sort of active optical stabilization as well, such as the piezoelectric image stabilizers which are on higher-end point and shoots or even cell phones now.

Carbon_Rod

Sun Jul 06 2014, 08:28PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Patrick wrote ...

but what if i have a single piston revolving at 8k rpm? i dont know how good or bad that situation will be...?

Most Piston based motors use a crank counterweight to avoid damaging the bearings.

Also note, a 2 blade system will generally require a stabilization bar on the rotors.

BigBad

Mon Jul 07 2014, 02:04PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
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Posts: 600

Tuned mass dampers are much lighter than simple mass dampers.

With a tuned mass damper you can halve a vibration with a mass that is a few percent of the thing causing the vibration.

With camera-type stuff it's very susceptible to twisting; translation does much less. You can damp twisting out by mounting it properly on bearings with axes right at the centre of mass so it doesn't couple, and then using a light damper/spring to pull it into the direction you want. High angular momentum is important; stabilising booms are very desirable. Gyros give the best angular momentum, but it's more mass.

Ash Small

Mon Jul 07 2014, 04:15PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

If you want to mount a piston engine on a drone (multi-copter), the rotors, if balanced correctly, should provide sufficient gyroscopic effect to damp the vibrations, especially if the motor-generator is suitably 'rubber mounted', suspended by elastic bands, etc.

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