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Thread: something different from galvo scanners?

  1. #11
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    For this sort of thing with steppers, you really need microstepping when positioing mirrors. Anaheim Automation makes nice, inexpensive, microstepping drivers.
    Example, a 400 step per revolution stepper can become a 12,800 step or 102,400 step unit with microstepping. Microstepping can also damp resonances before they happen.

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    they are called galvos and laser software??

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    Galvos are good only with comparably small mirrors
    No, galvos are good with any size mirror really. You just sacrifice speed as the mirror size increases.
    As you said that speed wasn't an issue, why aren't galvos still the most suitable solution?

    Given that 6mm isn't that large, just how big a mirror do you need to get the angle you want?

    For what its worth, I'm putting something together with nearly 6mm beam, and I'd like a reasonably wide angle from them, and I'm going the galvo route.
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    I have galvos moving 25 mm mirrors at 14k pps. I don't know what is wrong with you people.

    Steve

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    Quote Originally Posted by zorn View Post
    can you replace the mirror of a galvo with a bigger one yourself?
    Yes - of course. Several people in this thread have already suggested this to you.

    The problem with larger mirror scanners I found is their max scan angle decreases as the beam diameter increases, or rather part of the beam will be cut at high angles.
    Did you bother to investigate any of the suggestions posted above? Because Steve Roberts posted no less than 8 different scanner pairs that would have worked.

    One of his suggestions, the G330, is commonly used (or rather, was commonly used) to scan the fat beam from a copper vapor laser - and that beam exits the laser at over 1 inch in diameter. I personally have a set of G330's that are fitted with 1.5 inch mirrors, and they run with no problems. More to the point, I'm sure you could go much bigger on the mirrors and still get several Kpps out of them. (My 1.5 inch mirrors can do around 8Kpps, and they are huge, thick, heavy, chunky mirrors.)

    they are pretty costy for what I want.
    What, exactly, is your definition of "costy"? The E-bay auction that Steve linked to had a starting bid of $26, and as of this posting it still has 9 hours to go with NO BIDS.

    I paid less than $100 for my G330's, and they came with the mirrors, a mount, and a home-made amp to drive them. (Got them off E-bay.)

    An expensive scanner + DAC for slowly moving single fat beam not coming out from a projector doesn't seem like a good idea.
    You already have a DAC, and the scanners can be had for less than $30. You can drive them with an ordinary audio amplifier (just remove the DC-blocking caps). Mirrors are probably going to be the most expensive component, but if you don't need 99% efficiency, just buy some square first-surface mirrors and epoxy them to the galvo shaft.

    If you don't need multi-Kpps speeds - so what? You can always run the galvos slower. But using an off-the-shelf technology is always going to be cheaper than trying to cobble together your own solution.

    Adam

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    Quote Originally Posted by zorn View Post
    I don't understand the rudeness.
    I'm sure Dream, Cypher0 and Magnus could explain it to you.

    Seriously though - Steve was merely explaining his exasperation at having provided several solutions which you have ignored.

    I don't need 14Kpps. I already explained what I need.
    We know. The point is that you can get everything you need (and a whole lot more) using galvos. There's no reason to think about stepper motors (which are not any cheaper, and come with a whole new set of problems, and are slower as well).

    Regarding larger mirrors:
    I must be confused about something, I reread the thread and can't find any sentence which says that.
    The first reply to your post (from Flecom) suggested larger scanners and larger mirrors. Steve's first post also suggested larger mirrors.

    you missed my response to the idea of using old inexpensive galvos.
    If there are cheap old and slow galvos out there, the problem with requiring DAC is still there
    You need a controller for the stepper motors too, so it's a wash. And a sound card can be used as a DAC - that's about as cheap as it gets. (Certainly far cheaper and easier than buying a stepper motor controller and then writing your own custom micro-code to run it.)

    The cost as I've explained is not just about the cost of the galvos, but the amps and DAC too.
    Open loop scanners like the G330's can be powered by an ordinary audio amplifier. You just need to remove the DC-blocking capacitors. If you want to go really cheap, you can build your own audio amp using an LM386 and a few passive components. (Actually, you can probably save even more money by purchasing a monolithic amplifier already assembled for like $6.) Or you could rip the amp out of an old automotive tape deck. And we've already discussed the cost of a sound-card DAC.

    if I can buy something else cheaper that can run at the speed I need, why should I get 7 scanners and DACs, which I can't even afford right now?
    How many of these units do you need, and how many controllers do you need?

    If you plan to build 100 of them, it *MIGHT* be worth your while to investigate the cost of a stepper motor pair and a custom controller for each unit. Buying that many units *MIGHT* offer you a price break that could bring it into competition with a galvo solution. However, you would still have to do custom-programming for each controller, and it would be very difficult to make changes.

    I don't think that is something you want to get into, but if micro-code programming is your thing, then by all means: have at it.

    On the other hand, if you only need one of these things (or even just 7 of them), then galvos + a DAC (or even several DACs) is a much cheaper solution. More importantly, this is a solution that is ready to go right now with no engineering, programming, or troubleshooting required to get it working. It gives you excellent precision with regard to mirror position, and has the added benefit of being able to run faster than you currently need.

    And if you can't afford to do it for less than $200 per unit (including the cost of the sound card DAC, the scanners, the mirrors, and the amps), then you can't afford it right now and that's that.

    Adam

    PS: Note that in the case of multiple units, unless you need each set to be doing something different, you can run multiple scanner pairs off the output from a single DAC. You can't do that with a stepper controller. Each motor needs it's own controller.
    Last edited by buffo; 04-16-2015 at 06:15.

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    Quote Originally Posted by dream View Post
    flecom, you really need to try harder with this thread, man. :/
    To me there's been enough discussion whether galvos will work for whatever is needed here.

    Galvos are good only with comparably small mirrors. Even then there's the price difference (galvo itself + the "driver" + the DAC + the software).
    Have you never seen non-galvo scanners in other lighting equipment and even just cheaper lasers?
    http://www.americandj.eu/en/products...ts-led/scanner
    I've read it and I'm just confused, you can get galvos with large mirrors, just use galvos with large mirrors??? why re-invent the wheel...

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    I may have missed it, but how "fast" or "slow" are talking here? Are you wanting to scan geometric shapes and patterns or just sweep beams around. can you give an example of the effect you are after?

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    Quote Originally Posted by zorn View Post
    I already told you that I've responded to Steve's suggestion.
    Yeah, you blew him off.

    Admit it: you didn't even look up any of the specs on the galvos he suggested, did you? You made a few assumptions and blew him off with two statements: "They appear to be too expensive", and "I prefer to use servos". You didn't even know how much they would cost when you said that!

    That's why he got pissed at you. You have already decided in your mind that a servo or stepper motor is the solution you want, and you came here looking for confirmation, rather than advice. (Do you see a pattern developing here?)

    you're also assuming that basic programming on arduino isn't a solution for me, which in turn is assuming there isn't an open source code I could use.
    Well shoot - if you've got it all figured out already, then why are you asking us for help? Just go build the damned thing already and then come back here and amaze us with some pretty pictures.

    We've already given you our advice, and explained WHY we think galvos with large mirrors are a superior solution to using stepper motors. We've even offered low-cost solutions that are damned close to the cheapest stepper controller/arduino solution. And we've hinted at the trouble you will likely encounter with using steppers (not to mention the difficulty in adapting arduino micro-code - open source or not - to your application), yet you continually ignore us.

    So yeah, if you think you know better, go ahead and show us! Maybe we will all learn something from you. I, for one, would love to see your finished product (including a price breakdown) using stepper motors.

    But if you'd rather just argue with people than actually build something, then please go away. We all got sick and tired of that game long ago.

    Adam

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    Quote Originally Posted by buffo View Post
    We all got sick and tired of that game long ago.


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