lissajous Pattern laser light and sound project

[jbeng]

Those real laser mirrors are pretty strange, unless you get really close they look normal. But if you put them upto your eye you can see straight through them although its kind of smokey. I cant remember the proper name of them and its really bugging me lol.

The term you're looking for here is "dichroic mirror".

I think the beam spread is due to a normal mirror having the silvering on the back of the glass. You will get two reflections. One from the surface of the glass and the other from the silver on the back of the glass. The piece of mirror that came from a scanner could have been used both ways as there was no paint over the silvering as on normal mirrors. I expected the silvering to be soft and scratch easily if you try to clean it. It did mark easily so it must be some harder metal than silver vacume deposited. Using a disk platter as a mirror may solve this problem. When I was looking to see if anyone else had used this idea I found out that some disk platters are ceramic. All the ones that I have dismantled are hard aluminium alloy with a magnetic coating.

Yes, laser mirrors need to be first-surface mirrors with the reflective coating on the outside, else you have various reflections from the glass surface creating ghost images of the main beam. I have used pieces of aluminum HDD data platters as laser mirrors with good results. One of the best things about using the platters is that the aluminum can be easily formed into whatever shape is desired by cutting, machining, sanding or drilling. Glass on the other hand is not so easy to work with, as it breaks very easily. I believe the platters from small laptop-style HDDs are often glass or ceramic, so they probably wouldn't be of much use.

Most often, these devices used to move a laser beam, some at very high speed for animated graphics, are called galvanometers or scanners. They usually have a feedback sensor on the galvo (often capacitive) and use closed-loop servo amps for sensing the position of the moving parts.

Here's a link to how one guy built his own DIY projector system. It might give you some insight.

http://elm-chan.org/works/vlp/report_e.html

 

[large_ghostman]

Actually the word I was looking for was first surface thanks very much . I have dichroic mirrors that are large but an odd shape, not sure I fancy having a go at cutting them!

BTW Hi Jeff, you would need to see the mushroom vid in the first post to understand this isnt a projector project, it sounds like one and looks like one but it isnt one . Its an idea from another thread for doing an art project that puts sound into visible shapes, the sound defines the shape rather than the shape is defined and is linked to the sound (if that makes sense). If you watch the mushroom vid above it shows how a mix of sound and frequencies etc etc can build complex patterns on a O Scope, I have looked at the laser projectors alot and both the guy who did the v id and now me cant see a way to do it with mirrors.

I think its down to the angle of deflection etc etc, with no mirror you zero angle and thats kind of what you get on a OSCOPE. It matters because the sound and therefore the shape has to be done in programming software then he channels separated and recorded. In alot of ways the galvo's look like they would work if they could move the laser stage

 

[alec_t]

To waggle something at audio frequencies for creating a Lissajous pattern will require a light-weight moving element. I think waggling the mass of a laser would be out of the question for other than very low frequencies. How about use a short length of reflective ribbon, e.g. a strip of kitchen foil? If one end is anchored and the other end is moved by a loudspeaker cone you would have a tiltable micro-mirror for angularly deflecting a laser beam.

 

[large_ghostman]

To waggle something at audio frequencies for creating a Lissajous pattern will require a light-weight moving element. I think waggling the mass of a laser would be out of the question for other than very low frequencies. How about use a short length of reflective ribbon, e.g. a strip of kitchen foil? If one end is anchored and the other end is moved by a loudspeaker cone you would have a tiltable micro-mirror for angularly deflecting a laser beam.

I dont understand why you cant waggle a heavier mass if its mounted on say a point or bearing or even something else I have in mind. I will post it up after I have tried it properly but the levitation thing gave me an idea. I managed to levitate a ball bearing that was 5-6 times heavier and the frequency of oscillation from the control circuit was 16Khz, I had nightmares trying to damp it down.

So how about a HDD motor and plate, dont use the motor just use it as a mounting for the plate, then a couple of those small neo magnets almost touching and with a small coil above and below each. Top off with 2 hall effect sensors and H bridge, surely if the magnets are as close as I can get them (side by side) with a coil above and below each, I can wiggle the plate a small very fast and it should easy hold the laser. Then for the other Axis doe the same but attach first HHD contraction to the side of the other plate (I should mock it up and take a pic!!).

Hopefully that makes sense! a decent electromagnetic coil should move the plates with magnets fixed on no problem. I only need fairly small deflection, but I could use the you shaped HDD magnets and mount them on the plates near the center of the plate with coils above and below. Mount the laser near the edge away from the center, I have no idea if it will work but its something I got to try.

BTW the laser is around 5g

 

[4pyros]

Thinking out of the box, I wonder if you could use audio frequencies to PWM a motor spinning something?

 

[alec_t]

I dont understand why you cant waggle a heavier mass if its mounted on say a point or bearing or even something else I have in mind.

You can waggle it, but for a given acceleration the force required is proportional to the mass being moved.

 

[large_ghostman]

we gonna need a bigger coil

 

[Les Jones]

I agree with alec_t that the mass needs to be kept to a minimum. (Or to be more precise the moment of inertia.) Even without the mirror attached to the disk drive in my picture the amplitude of movement became very small above 100 HZ. This was driving the actuator using an audio signal generator into a TDA2050. I did consider trying to reduce the mass of the moving part of the actuator but was too lazy tos set it up on the rotary table on my milling machine to do this. I think you will only be able to use the lower frequency components of the audio signals to produce the patterns.

Les.

 

[large_ghostman]

Ok I cant do anything until the laser gets here. But I am convinced some decent coils pushing and pulling on magnets will do it. I wont go into detail at the moment why I have dismissed mirrors but I do have a good reason, I am taking all you say onboard but I also using some of the past things I have done for a guide. At the moment I have two areas of attack I need to try if only to rule them out, the other thing nagging at me is I am aware when reading back my posts that they dont explain whats in my head, So it might be easier to just mock something up, it gets frustrating when you see something clearly in your head but cant express it correctly!!

It will work even if I have to stand there and shake it by hand

 

[4pyros]

Ok I think I am getting an idea. Mount your laser head on a compression spring so that the beam is in the same plane as the spring.
Mount the other end of the spring to a fixed point. Now your laser will have 360 degrees of movement.
With electromagnets around the laser assembly you can pull the laser anyway you want.
Kinda like how the yoke coils on a CRT can deflect the beams to draw on the screen.
Am I close to what you are thinking LG?

 

[large_ghostman]

Ok I think I am getting an idea. Mount your laser head on a compression spring so that the beam is in the same plane as the spring.
Mount the other end of the spring to a fixed point. Now your laser will have 360 degrees of movement.
With electromagnets around the laser assembly you can pull the laser anyway you want.
Kinda like how the yoke coils on a CRT can deflect the beams to draw on the screen.
Am I close to what you are thinking LG?

Almost!!

I am really rubbish at describing a picture in my head! I will mock a non working version in the week so you know what I am on about, I have two approaches I want to try. One is rails similar to a ink jet printer and head, only the laser would be the inkjet head and there would be another axis that is tied to the first set of rails. Both would use a set of push pull coils each side of a magnet. The up/down axis on start up would float to center position + around 10mm. the horizontal axis would have a set of coils and magnets each side of the laser mount.

The big problem I have is the oscillation and compensation when using electro magnets like this, the only thing I think might be in my favor is the laser shouldnt show the tiny movement too much if I set the distance right from magnet to coil. I am starting to doubt its going to work, so for now back to the other system which is also needed and simpler, this also gives me a solid fall back if I need to abandon the fancy way then I still have a project and no one will know its only half of what I planned . Maybe a bit of soldering time making a spinning mirror will do my brain good . I am going to use stepper motors instead of fans for the rotation, and use HDD platters cut and screwed to the motor centrally. This way I get around the problem of a hole in the center or a HDD platter hub thats in the center. Should be fun trying to cut a platter so its round!!

My bigger problem is my main project the MKII, the motor that blew has done more damage to the board than I first thought. Bad design and shouldnt have happened, I need to introduce better switching on the H Bridge and have better current monitoring and heat sensors on the Bridge as they dont have large heat sinks. Not a major problem but I was trying to shave a few grams off.

I have used a cordless drill motor to see if it would be any good run as a generator from a petrol RC plane engine, I stuck it in the pillar drill and ran at around 6K RPM. I might just get away with it as long as i keep to no more than 3 motors on at a time, I might have to get clever when I need all six on. But that is all experimental and at the moment just a side idea, main focus is to shed enough weight to compensate for the added components. I might switch one or two idea and get a wifi unit for the PI rather than the arduino, it all depends on weight. No way am I shelling out £300 for a battery!! That is a nonsense price!!!

 

[4pyros]

Almost!!

I am really rubbish at describing a picture in my head! I will mock a non working version in the week so you know what I am on about, I have two approaches I want to try. One is rails similar to a ink jet printer and head, only the laser would be the inkjet head and there would be another axis that is tied to the first set of rails. Both would use a set of push pull coils each side of a magnet. The up/down axis on start up would float to center position + around 10mm. the horizontal axis would have a set of coils and magnets each side of the laser mount.

The big problem I have is the oscillation and compensation when using electro magnets like this, the only thing I think might be in my favor is the laser shouldnt show the tiny movement too much if I set the distance right from magnet to coil. I am starting to doubt its going to work, so for now back to the other system which is also needed and simpler, this also gives me a solid fall back if I need to abandon the fancy way then I still have a project and no one will know its only half of what I planned . Maybe a bit of soldering time making a spinning mirror will do my brain good . I am going to use stepper motors instead of fans for the rotation, and use HDD platters cut and screwed to the motor centrally. This way I get around the problem of a hole in the center or a HDD platter hub thats in the center. Should be fun trying to cut a platter so its round!!

My bigger problem is my main project the MKII, the motor that blew has done more damage to the board than I first thought. Bad design and shouldnt have happened, I need to introduce better switching on the H Bridge and have better current monitoring and heat sensors on the Bridge as they dont have large heat sinks. Not a major problem but I was trying to shave a few grams off.

I have used a cordless drill motor to see if it would be any good run as a generator from a petrol RC plane engine, I stuck it in the pillar drill and ran at around 6K RPM. I might just get away with it as long as i keep to no more than 3 motors on at a time, I might have to get clever when I need all six on. But that is all experimental and at the moment just a side idea, main focus is to shed enough weight to compensate for the added components. I might switch one or two idea and get a wifi unit for the PI rather than the arduino, it all depends on weight. No way am I shelling out £300 for a battery!! That is a nonsense price!!!

I can't wait to see what you come up with, but I think I had a good idea.
I think a dremel motor would be faster.
What kind of battery lithium?

 

[large_ghostman]

Probably some kind of main psu

 

[Les Jones]

Is it possible that one of the brushless motor as used on model aircraft with it's control electronics removed and replace by a three phase bridge rectifier would be better than a cordless drill motor working as a generator ? It would be like a miniature car alternator but with a permanent magnet rotor. I have never played with these motors so comments from someone with experience of this type of motor would be interesting.

Edit.
I have jut realised that I have put this in the wrong thread.

Les.

 

[large_ghostman]

I can't wait to see what you come up with, but I think I had a good idea.
I think a dremel motor would be faster.
What kind of battery lithium?

Sorry I was miles away! I was talking lasers you were talking hexapod lol. The battery I have is a type of Lithium Polymer, its normally used for laptop batteries but this one has no casing etc. It fits in a charge unit but takes forever to charge up!. I dont know about the motor Les, I chose the chunky cordless motor because the main motors can pull over 10A at times. Its something I need to play with carefully, I have already had burnt boards because of current draw. I know some commercial copters use a generator/alternator, but there seems to be a trade off with weight etc. No easy answer as no solution is perfect, I will try as many motors as I can get hold off.

I need to see if anyone at school has an old airplane engine I can try first, it might stall the moment the generator is asked to provide a high current. Having said that there is a post ages ago I made about making a hexapod with mobile phone batteries and small motors from disk drives or from old floppy drives. Could be done etc etc etc, saw on the TV at the weekend you can buy a kit that clips to your mobile phone to turn it into a quadcopter, uses the motors from small HDD!! And the phone battery . I bet it sells well and makes a fortune

 

[4pyros]

Sorry I was miles away! I was talking lasers you were talking hexapod lol.

No you had had it right I was talking about deflecting a laser.

 

[large_ghostman]

I will be going with just spinning mirrors for the school project, the other will take alot more work. I will pursue it as a side line but dont have enough time to get it fit for the exam, I found making the table move pretty easy, I found making it move in two axis pretty easy. I have even found getting the sound to make the table act like in the mushroom video EASY!!

What is not easy is damping down the elctro magnets so they only move to the frequency you put through them, the problem seems to overshoot and undershoot with the opamps and hall effect sensors. What you get is the center is fine but you get bad distortion and break up when the opamp adjusts the electromagnet to keep it inline with the frequency supplied. I am pretty sure clever feedback might be able to sort it out, but at the moment its not usable for what I want. I am still sure it can be done and I am also sure the mushroom vid is better without mirrors, but I need stiffer control on the amount the base moves. So for now I will concentrate on the spinning version and then do the other when I get a little more time.

I tried it with the other laser I managed to find, but my driver still seems wrong as the laser has suffered. It was brought as 1mW but I am sure its alot more, it will be interesting to get it working but not for the exam, it just isnt worth the effort at the moment for an Art exam. I have bigger things I need to sort out on the Hexapod, I am having to strip more of the project back than I wanted. Also the massive reduction in time is really messing me up, I am not as confident with it now and making mistakes.

I need a couple of days break from it and attack again, I am getting bad H bridge trouble, I know I should use a driver but for all kinds of reasons I cant go into at the moment, it was/is better to build my own. I am aware the dont switch off cleanly and when I am able to tell you how I drive the gate you will no why its being a PITA. I dont mind it not switching cleanly at the moment as the exam will mean its on for a max of 11 mins (if I can squeeze the battery that long). I have decided to take a risk and redo the main micro board, I want to distribute the weight better. I am starting to hit the limits of what I can add weight wise and how much flying time I get.

I am going to boot the PI and boards and get the gyros calibrated with mains power, then switch to battery for the actual exam flight. The booting etc takes around 45-75 seconds, dosnt sound much but makes a difference when your shaving a gram here and a gram there lol. I have two new motors I will take a pic of tomorrow, they are the same as 3 of the others. The different motor has a little more power but dosnt seem to make much difference as most the time 80% is considered flat out, the extra 20% is used for maneuvers etc. It kind of gives a buffer when you get something go wrong and it has to self level, I found it better to have 20% in reserve so it can react by upping speed in a motor rather than decreasing in another.

I wont be watching the video again until I have finished!! I found too many things I wasnt happy with and didnt know about until I saw the video. I have gone from loving the project to hating it lol, the bloody thing will be up for sale after the exam lmao (only kidding).

So many questions I would like to ask but not allowed, and I wouldnt break the rules.