Mechanical: XY low power Laser steering

[NivagSwerdna]

For a home project I would like to take a low power fat green laser module eBay auction: #132039940489 and steer the beam around the outside of my house to deter the pigeons that seem to have moved in.  The control would be a simple pattern(s) to follow slowly during a few limited hours at night.

Basically I either need to steer the module up down left right or shine the module on a mirror and guide this. 

I've never done anything mechanical like that before... are there good designs that are simple to DIY?

Thanks in advance

(For my application the rate of rotation can be 'slow')

[chris_leyson]

Hi, you can pick up a cheap dual axis galvo scanner on ebay or less than £100, http://www.ebay.co.uk/itm/20Kpps-HightSpeed-galvo-scanner-for-laser-lighting-NEW-/220678256510?hash=item336172f77e:g:v1oAAOSwzgRWynrk

[BrianHG]

Google 'laser xy mirror'
There are cheap speaker solutions, to stepper motor solutions, to more professional device solutions.

Example cheap solution:
http://www.instructables.com/id/Arduino-Laser-Show-with-Full-XY-Control/
More DIY:
http://hackedgadgets.com/2006/12/02/ten-dollar-xy-laser-scanner/

[ajb]

While a fat 50mW beam is a far cry from the multiwatt handheld pointers that are available, you're still looking at a level of laser power that requires some care to use safely.  Hopefully you are intending to arrange this in a way that somebody (like your mail carrier, delivery drivers, or utility workers, or nosy neighbors) can't just walk up and get a beam in the face.  Since that's a DPSS green, there may be a significant IR component that you won't notice until it's too late. 

I don't know about the UK, but in the US the FAA has very stringent limits on the amount of laser light that can enter navigable airspace.  In the most restricted zone this limit is 50nW/cm^2, and in the US people HAVE gone to jail for striking aircraft with lasers.  I wouldn't undertake this sort of project here in the US without putting a LOT of thought into making sure that the beam couldn't possibly go past my house and potentially out into airspace.  I say that having done the FAA paperwork for much more powerful lasers in unterminated outdoor light show situations, it's serious business.  For the curious, AC70-1 is the FAA document that explains the limits and all of the required calculations.

All that aside, the listing doesn't say what the actual beam diameter is, but if the housing is 22mm, then the beam is probably something like 14-18mm at a guess.  That's doable with galvanometers, but not the sort that you're likely to find as a cheap complete set on eBay.  However you can use the same sort of dual axis scanning arrangement just with larger mirrors attached to the mechanical actuator of your choice in place of the galvos.  Stepper motors would work, but would have pretty limited resolution--the angular displacement of the beam is going to be twice the angular displacement of the mirror, so a 1.8º stepper is going to give you 3.6º of beam motion per step.  Microstepping is of course an option.  One thing to note with steppers is that a mirror big enough to scan your beam is going to result in significant mechanical resonance in combination with the motor, so the beam position will jitter around noticeably after a step before settling.  Hobby servos would probably give you better resolution with the right MCU configuration, but servos are not exactly known for their stunning repeatability and stability.  A small gearmotor with an encoder would probably be the most accurate option for not an extravagant cost. 

I would avoid at all costs any sort of kludgy system involving any of the following for the reasons mentioned in the first two paragraphs:
- Speakers as actuators
- salvaged hard drive components
- hot glue or bamboo skewers as structural elements

[NivagSwerdna]

I don't know about the UK, but in the US the FAA has very stringent limits on the amount of laser light that can enter navigable airspace.  In the most restricted zone this limit is 50nW/cm^2, and in the US people HAVE gone to jail for striking aircraft with lasers.  I wouldn't undertake this sort of project here in the US without putting a LOT of thought into making sure that the beam couldn't possibly go past my house and potentially out into airspace.  I say that having done the FAA paperwork for much more powerful lasers in unterminated outdoor light show situations, it's serious business.  For the curious, AC70-1 is the FAA document that explains the limits and all of the required calculations.

That's a very good point.  My intention was to only have it scanning an area backed by a wall/roof line and approx 10ft off the ground at the lowest.  But your point about stray light is well taken.  Given I'm near LHR I 101% agree I don't want any light going upwards.  In terms of power I think I've probably overdone it... I'm going to look at a much lower power/narrower unit to start with.

[Siwastaja]

No. You are not going to build a device that scans 50mW laser outside. Building this is extremely dangerous to your surroundings, and needs proper approvals, for a very good reason.

It is nontrivial to guarantee that the safety mechanisms to shut down the laser in case the scanning stops work well.

This will cause instantaneous eye damage to anyone, and it's not easy to control that the beam stays within your property, because it's a laser beam that goes far away.

[tggzzz]

For a home project I would like to take a low power fat green laser module eBay auction: #132039940489 and steer the beam around the outside of my house to deter

Stop. Right Now.

50mW is far too powerful - dangerously powerful. Look at the eyesafe limits; they are around 1mW. If that beam entered someone's eye, for whatever reason, they would be blinded. it doesn't matter if it was a software fault, the mirrors became misaligned, there was a reflection, a child wandered into the property - they would be blinded.

I really don't care if you blind yourself. I do care if you blind others.

If that beam went into my eye then I would be blinded and I would then have to find a way of committing suicide - but not before I had found a way of preventing you passing on "stupid idiot" genes. Yes, really. (I'm deaf; think of the consequences of being deaf and blind)

[NivagSwerdna]

Stop. Right Now.
50mW is far too powerful - dangerously powerful. Look at the eyesafe limits; they are around 1mW. If that beam entered someone's eye, for whatever reason, they would be blinded. it doesn't matter if it was a software fault, the mirrors became misaligned, there was a reflection, a child wandered into the property - they would be blinded.

Wow!  Thanks for the info.  It seems that Class 2 would be the max to even consider and that's 1mW.  I didn't realise how ridiculously powerful those things on ebay were!  Even the KY-008 red laser diodes exceed that.

I had found a way of preventing you passing on "stupid idiot" genes. Yes, really. (I'm deaf; think of the consequences of being deaf and blind)

We know you are coming.

[NivagSwerdna]

STOPPED!

Sense has prevailed.  I'll get back to my Nixie Clock.   

Happy New Year!

[Siwastaja]

Maybe you could try coexisting with the pigeons. Form a healthy friendship, if not relationship, with them.

[NivagSwerdna]

Maybe you could try coexisting with the pigeons. Form a healthy friendship, if not relationship, with them.

If they stopped cr****ing down my walls and over my window sills that might work.  I'll just have to get an Eagle or put up a few anti-perch bird spikes, the later looks more feasible.

[tggzzz]

Maybe you could try coexisting with the pigeons. Form a healthy friendship, if not relationship, with them.

If they stopped cr****ing down my walls and over my window sills that might work.  I'll just have to get an Eagle or put up a few anti-perch bird spikes, the later looks more feasible.

Eagles won't work. Kestrels are too small. Buzzards will only eat them once they are carrion anyway. Peregrines falcons snack on them, and are becoming common in city centres (e.g. London, Lincoln, Bristol, Bath).

Anti-bird perch spikes also seem to work.

[SeanB]

Try getting some Hotfoot, which does work well till it washes away. Poor man's substitute is a thick vaseline coating, as they will not want to roost on slippery slopes.

Spikes are generally a perfect roosting place after they drop some twigs there on them.

[Skimask]

I've got 2 pistols and a shotgun...and I'm not skittish about using them on small animals.

[Alex Eisenhut]

[tggzzz]

I've got 2 pistols and a shotgun...and I'm not skittish about using them on small animals.

Try that here and you will be having a long vacation at everybody else's expense.

[Marco]

Maybe use fishing line on the sills so they can't sit there?

For something more high tech, I wonder if those ultrasonic speakers which create sound through nonlinear mixing would be good to chase birds away. Detect bird on camera and create a sound source where they are at to scare them off (the actually audible sound wouldn't be very loud, because it's created right where they are at).

[Cerebus]

I've got 2 pistols and a shotgun...and I'm not skittish about using them on small animals.

The open outdoor use of firearms in London, especially near LHR, would bring the immediate attention of the kind of people you wouldn't want visiting you. 

As a matter of curiosity, there are no less than two civilian shooting ranges within spitting distance of Heathrow. One partially open air (the firing direction actually faces towards the Heathrow runways and any accidental over-shots would probably hit the BA maintenance hangers) and one totally indoors.

[mark03]

A while back there was some guy using a water gun plus clever machine-vision processing to deter squirrels.  Apparently the squirrels got used to it, but maybe it would work on your pigeons?  At least the worst-case scenario is a lot more benign than getting blinded or shot.

http://pyvideo.org/pycon-us-2012/militarizing-your-backyard-with-python-computer.html

[BrianHG]

I retract my comment.  Though it would be fairly harmless to the birds, it is potentially very effective and the last thing I need is a product being produced and sold out there which does nothing but annoy the hell out of pigeons for whoever buys it thanks to me.

[CatalinaWOW]

I don't know of any "Do and forget forever solutions" for pigeons.  Bird spikes do work well in many situations, and even when they drop sticks on them, it is just a matter of periodic maintenance.  Unfortunately that maintenance usually involves ladders and worse.

Some things that sometimes work that are potential hobby related activities:

An animated owl or falcon.  Just something that moves the head or wing periodically.  The birds figure out that it isn't harmful sooner or later and ignore it, but that can be delayed by more random or realistic animation and by moving the animated predator around.

A model railroad running along the wall edge.  Maybe even have a pigeon detector which activates the motion.

Mirrors to reflect the sun.  It would actually be a fairly challenging hobby task to design a system that would reflect the sun around in a pattern that was similar to your original laser based plan.  Would require at least couple of reflector/scanners to cover the entire day, and some significant math and analysis to translate sun location and mirror angles into a spot at the desired position. 

[SeanB]

There are commercial sonic bird repellents, and they use a random chirp of various volume, duration and frequency, that is done out of assorted waterproof speakers during the day till a little after sunset. Seems to work, though I have doubts for long term use, as they get used to it fast.

Light is also a commercial project, using a small tetrahedron of mirror glued together, with it being rotated by the wind, and sitting on a low friction pivot on a post, with you having a few on the area to be covered. somewhat effective, as I see quite a few around here, and those buildings are a little less prone to having the roosting birds on them.

[TechnicalBen]

On Radio 4 Gardner's Question Time they recommended some small wire. Plastic risks being chews by mice/rats. But metal would last longer. It prevents them from finding somewhere to land if arranged right.

This site has an example (half way down): http://www.pigeoncontrolresourcecentre.org/html/diy-pigeon-deterrent.html