Page 2 of 3 FirstFirst 123 LastLast
Results 11 to 20 of 22

Thread: DT-40's

  1. #11
    Join Date
    Apr 2006
    Location
    Orlando, FL - USA
    Posts
    1,719

    Default

    The reasons for my recommendations are several fold.

    First and foremost, as Spec said, it's an industry standard. One example of this is that all of the content that we currently distribute with our software was designed to be run full size, at 30K, with standard Cambridge scanners (or clones). Also the "default settings" found in our software are for 30K. We make the assumption that people will have an ILDA-standard projector with 30K scanners.

    Second, along the lines of what Spec said -- if you have standard Cambridge 6800 scanners, or especially clones, they were essentially designed to be operated at 30K. If you operate them at faster than 30K, you will unwittingly be making sacrifices. The servo component selection in the Cambridge CB6580 and several derivatives do not have the phase margin for faster-than-30K operation. Also, usually the mirrors are not thick enough, so you will begin to excite resonances in the system. The result of one or both of these is that there will be overshoots or other undesirable artifacts. These may only show up in certain images. For example, if you take a VERY close look at the DT40 image, you will see some differences. The green square in the center has overshoots on all four corners, and the white lines underneath that look like an "upside-down ground symbol" are a bit twisted, especially the bottom-most line.

    (For those who have changed the component selection of the CB6580, making themselves feel better that they didn't copy the Cambridge design, well, sorry but you have most likely only made matters worst.... I have seen this many times.)

    Third, also along the lines of what Spec said, if you take this 30K system and tune it faster than 30K, it will be putting in more current for a particular move. This "more current" tends to heat up the scanners faster. If you have Chinese scanners, one thing we have learned on this forum is that the coil is not formed as well, and not bonded as well to the stator. Thus, this is a good way to reduce the life of the overall scanning system...

    There are scanners and amp combinations that were specifically designed to operate faster, such as the Cambridge model 6215 and 671xx high power amp. These can operate at the same scan angle as Cambridge model 6800, but with truly twice the speed. In other words, you can take the "Sample rate" sliders in LD2000 and move them up to 60K, and play them back on these scanners with no other changes to the imagery. No additional points need to be added.

    As I said in another post, if you want to scan twice as fast, you must do your job four times as good, because there is a "square law" in the formula which dictates power required to do this. In the case of the Cambridge model 6215, the thermal conductivity is four times as high as it is on a 6800 and 6210. This, along with other factors are what allows the system to scan at 60K. Anyway, it just isn't very wise to take a motor system that was designed to operate at 30K, and operate it faster.

    If we have a pre-SELEM meeting in or around Pangolin, I will invite you to check out our "scanner lab", where we build scanners for industrial and military applications. I will also show you software we wrote which accurately predicts the coil resistance and inductance, torque, inertia and other properties of scanners. Rest assured that if I make a recommendation, it is made from a position of knowledge, and not just another opinion...

    Best regards,

    William Benner

  2. #12
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,382

    Default

    Quote Originally Posted by Pangolin
    Rest assured that if I make a recommendation, it is made from a position of knowledge, and not just another opinion...
    ummm... :? I don't recall ever saying that you weren't knowledgible, Bill. I just wasn't clear about the reasons behind your recommendation.

    That's why I asked you for more information. I didn't think it was your opinion, I just wanted to learn some of the science behind the fact, which your post explained quite nicely, thank you.

    I understand that you are quite busy, and we do appreciate the time you spend here. But part of the function of forums like these is to help people learn, and that can only happen if things are explained.

    Sorry if my request sounded insulting to you - it wasn't meant that way in the least.

    Adam

  3. #13
    Join Date
    Apr 2006
    Location
    Orlando, FL - USA
    Posts
    1,719

    Default

    Hi Adam,

    I did not interpret your inquisitiveness as an insult or a challenge.

    My final comment was just meant to add a little bit of final information for others who are reading this, and who might one day read it, and wonder about the authority of individuals doing the talking

    Best regards,

    William Benner

  4. #14
    Join Date
    Feb 2005
    Location
    Florida
    Posts
    802

    Default

    Very well put Bill ! Makes lots sense.
    "My signature has been taken, so Insert another here"
    http://repairfaq.ece.drexel.edu/sam/laserfaq.htm
    *^_^* aka PhiloUHF

  5. #15
    Join Date
    May 2006
    Location
    Native Floridian
    Posts
    3,081

    Default

    Wow, thanks for the compliments folks! I feel that this one could be better if I would spend some more time on it.


    That was VERY nice! Where's the rest of the album? It's much better than my popelscan abstract show. Makes me want to get my alphalite goin.
    Still in my head! I just need the time to work on it...

    What scanners and software did you do the video show with?
    It looks really smooth for the ammount of graphics in it, or is it several videos overlaid?
    What scan rate and angle was it?

    It looks great

    Jim
    Jim, when I wrote the show, i was using EMS-3080 (Eyemagic) scanners tuned at 30Kpps and Pangolin pro. Last night I used the older DT-40 scanners and recorded it with my Sony cybershot camera, which would explain the poor sound quality. Its one solid video, no cuts or editing. The camera did seem to have a issue with focusing throughout, but it turned out ok for a camera that was more designed to take still pictures! As far as scan rate and angle, I had pangolin set for 30K and was probably pushing 25 degrees peak to peak for the video.

    Awesome mate i loved it ...... i think that video is the first one laser show I have ever seemed timed to music .......... what you have done there just seem soooo above my abilities ....... and I imagine it would sooo time consuming to do so . I am harbouring some thoughts I would love to do a laser show connected to the BBC NEWS 24 countdown music but goodness knows if it will ever happen !.
    Well I'm glad you enjoyed it! With pangolin, syncing laser images to music is just as easy as can be. Being from the planetarium environment, I do prefer full graphic shows synced to music. It takes alot of creative talent though...

    Nice show!!
    Wow, thanks Bill! That means alot to me coming from you! 8)


    David

  6. #16
    Join Date
    Jan 2005
    Location
    Norway
    Posts
    1,301

    Default

    wow that was a very nice show (want to share it?) 8) 8) 8)

    That show did seems like a professional show for me !
    The galvos did run very nice, I think they did better than mine :? maybe I need to tune then correctly...

  7. #17
    Join Date
    Jun 2005
    Location
    SoCal
    Posts
    504

    Default

    Nicest laser show on google!

    Offtopic:

    Hi Bill, you're the man to ask... This is something that I've been looking for input on...

    Of all the scanner/amp combos I've used (and I have quite the stack), the Catamp IV + 68k from Medialas has given me the most adjustability and highest scanangles at any set speed. And the scanners still run cool. I get perfect tuning from it at unnaturally wide angles (compared to others amp/scanner combos) even though I've been abusing that particular set for over 10 years. I've been using the CT6215+amp combos recently even though I prefer the older 68k's since the newer 6210 design appears more bulletproof (I've blown tons of fuses using the Medialas' microamps). But I've noticed that even the 60k+ amp is a lot less "stable" (if that's the word) than the old catamp beast.

    This leads me to suspect that the current amp designs aren't getting the performance that the actual scanners are capable of... What are your thoughts on where we can improve the amp design? I've been looking at going a DSP route for the scanamp (skipping the normal slew of knobs'n dials) and running the actual PD at a higher rate than normal and using a >+/-30V drive on the coils to move them a bit faster. Cooling could be an issue, but I think with proper drivers it could even run cooler than the standard $2 audio amps which are currently being used. It'd be similar in concept to the PID tuning on very high-end servos.

    ObOntopic: We've been putting a DT40 (don't know which model. Spec?) through the paces... The drivers are very close in design to the cambridge design, and exhibits some of the same peculiarities. There is a reduced range in the HFD and LFD compared to a true CT driver and I'd like to see some more pots for adjustability in there... but it's easy to tune the system to be acceptable to most folks... The stock power supply is a hair bit undersized to get the performance the scanners are capable of. When tuning, I found bearings are definitely not as nice as CT's as I have to do a bit more damping than on a CT.

    In terms of raw performance, the same amount of tuning required to make a CT unbelievable is what it takes to make these behave like a factory tuned matched CT scanner/amp pair.

    Which is not bad when you could buy 4 of these for a nice set of CTs

  8. #18
    Join Date
    Apr 2006
    Location
    Orlando, FL - USA
    Posts
    1,719

    Default

    Of all the scanner/amp combos I've used (and I have quite the stack), the Catamp IV + 68k from Medialas has given me the most adjustability and highest scanangles at any set speed. And the scanners still run cool.
    I really can't speak to that particular amp. Before MediaLas got into dealing in Cambridge amps (back when they were doing mostly Catweazle II and WideMove), they did send me a number of scanners and amp designs on which to comment. I always found problems and made recommendations. But, based on the problems that I found, I was never very impressed with the engineering... Of course, they might have learned a thing or two since then, but I have a tendency to not trust engineers once they make a mistake, and demonstrate bad engineering a time or two. Of course, I'm a really quirky guy too...

    However, to answer your question about this particular scanner/amp combination, I would need to do some more investigating. We have a Stanford Research SR-785 Dynamic Signal Analyzer which I would use to do some of the analysis, along with a normal scope. Since most of what you say is qualitative rather than quantitative, I would need to verify the extent of what you are saying (how much wider, how much cooler, etc.)...

    If this is seen on only one set of scanners, it could be that the KT (torque constant) of that one particular set is on the high side of normal. I have seen Cambridge scanners shipped that were 12% below their spec KT. It could be that you have one set that is 12% higher or so...



    even though I've been abusing that particular set for over 10 years.
    Yes, I had a very old set of 6800s that I used until recently myself. They were the original, with single LED shadow cast design. It is only recently that I changed that particular pair out for a newer double-LED pair. Cambridge scanners always lasted a long time for me...



    I've blown tons of fuses using the Medialas' microamps
    That's believable... In early scanner amps from MediaLas that I have seen, he actually removed the RC4200, which is the main part of the coil temperature calculator. It's the first line of defense against overheating the scanners, and (when the circuit is designed properly) it will limit the RMS current to 1.5 amps. If that is in place and you have an appropriately-sized fuse, then you won't blow the fuse. If this is not in place, you will blow fuses even if they are appropriately-sized.

    Remember what I said about not trusting engineers after I have seen a mistake?



    What are your thoughts on where we can improve the amp design?
    Well, if you are talking about Cambridge 6800 or 6215 scanners, my thoughts are that it will be difficult to beat the performance!! I participated in the design of the original Cambridge CB6580, along with former Cambridge president Bruce Rohr. For 30K scanners, all of the components selected are perfect, and if you change any component, you will degrade performance. (That's why when people copy the Cambridge design, but change a few components to make themselves feel better that they didn't just rip it off, they always wind up with lower performance... And unfortunately, I haven't seen a single amp running Cambridge scanners that wasn't a copy of the original CB6580 design...)

    Also, when Cambridge came out with the 6210 scanner, Bruce Rohr had left (Cambridge had been bought out by Accel and Bruce walked away with a few million dollars...), and I was not working very closely with Cambridge at that time. So the component selection in the 671xx amp that drives the 6210 is compromised in my opinion. Large angles are not as fast as the original 6800/CB6580 and there was a really high frequency oscillation in the output stage that showed up under certain circumstances, and would heat up the coil even when you weren't scanning. For the 6210s that we have at Pangolin, I made some component changes. But I fear that people who copied the component selection in the 671xx drivers for the 6210 are getting really sub-optimal performance...

    For the 6215 scanner with either 673xx amps or 671xx high power amps, once again, it will be difficult to improve performance. If you want to go faster than 30K with the 673xx amps, there is a single resistor you can change to give yourself some more room on servo gain. The range of that pot was purposefully limited so that you can't get much faster than 30K (because, again, that's the standard, and also because that's the rate at which the servo was designed). Similarly, the 671xx is limited to around 60K, but you can change a resistor and it will go around 80K. But if you go faster than 60K you get into phase margin problems (which is why things are limited)... The latest 6215 and 671xx or 673xx designs are really optimized, and this is the only thing we recommend at Pangolin.



    I've been looking at going a DSP route for the scanamp (skipping the normal slew of knobs'n dials) and running the actual PD at a higher rate than normal and using a >+/-30V drive on the coils to move them a bit faster.
    Well, I have done a number of DSP designs in the past. If you poke around on the "pending" section of USPTO, you will find a complete laser projection system there that I worked on, based on a single Analog Devices DSP that did everything, including manage the imagery and two-axis servo. But to me the downside is cost. It will be tough to beat the low cost of an analog servo. And the problems with analog are not really problems in my opinion... Even Cambridge has a digital design now, but they don't routinely sell it... Also, for these small scanners, the sample rate of the DSP will need to be around 200kHz or faster. It’s really expensive to do a good design and do it right…


    Best regards,

    William Benner

  9. #19
    Join Date
    Mar 2006
    Location
    East Coast , Canada
    Posts
    285

    Default

    All this talk of scanners reminds me i need to send my set to you Bill for mirrors and alignment.. How busy are you these days? How would the turn around time be to get my 6800's back to shape?? Thanks.. Carey
    CREATIVITY AT THE SPEED OF LIGHT!
    www.laser-ad.com

  10. #20
    Join Date
    Apr 2006
    Location
    Orlando, FL - USA
    Posts
    1,719

    Default

    Hi Carey,

    February seems to be a consistenly slower month at Pangolin. That would be a good time.

    Bill

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •