Review of ScanEco20 galvos from LaserShowParts.com

[buffo]

I've been meaning to complete this review for nearly 4 months now. Dave and Aijii at LaserShowParts.com volunteered to send these scanners to me so I could review them back in July! (Yeah, I know... Cut me some slack - things haven't exactly been going so well for me.) Some of you may remember that I started this review before SELEM 2007, but lost all the pics due to a bad memory card. So I had to start all over. (sigh)

I'm happy to say that the review is now complete. So let's get started:

First, a disclaimer: I am not employed with LaserShowParts.com, and I was not paid or otherwise compensated in any way to perform this review. All the tests were performed using my Pangolin QM-2000 intro board. (I did not test the DMX-compatible lasershow player board that came with the scanners.)

The ScanEco 20 galvos come with slightly larger mirrors than other scanners you may be used to. The mirrors are rectangular and measure 7mm by 11mm. I measured the reflectivity at ~ 94% for each mirror at 45 degrees. That works out to a total loss of 12% across the galvo pair, which is only slightly worse than the mirrors on my DT-40's. (I loose around 10% total across my DT-40's) Note that the factory spec for these ScanEco 20 galvos is 90% or better for each mirror, so they're much better than spec...

Before I tuned the scanners, I fired them up first to see how they performed right out of the box. And while they did work, they were not tuned very well. I noticed some distortion and bowing in the test pattern. Also, the circle was way outside the square, and there were large overshoots on the corners of the square.

I loaded a different frame and increased the size to maximum so I could check the max scan angle. I measured 63 degrees.

This being done, I started tuning the scanners. I originally tried to follow the guidelines listed on the laserfx.com site, but after an hour's worth of tweaking, it didn't seem to be getting much better. So I decided to use Bill Benner's technique. I walked the gain down in steps, all the while dialing back on the high and low frequency damping, until I got down to zero gain. Then I loaded up the squarewave quadrature pattern (draws a square) that comes with Pangolin and started raising the gain. Each time I bumped up the gain a little bit, I had to adjust the low frequency damping to compensate for the overshoot. Eventually, I needed a little high-frequency damping as well. (The process is very similar to this procedure that Steve Roberts was talking about a while back.) Once I get the video from Aaron, I'll try to put together a tutorial explaining how this works.

After about an hour or so, I had it looking pretty good, so I switched to the ILDA test pattern. I increased the size until the circle didn't get any larger, then backed off a couple percent and started tweaking the tuning. After another 30 minutes or so I had it dialed in really tight. Scan angle on the test pattern was 10.5 degrees, with the speed set right at 20Kpps.

The next test was to load up a complex abstract and let the scanners work for a while. I let them hum away for around 90 minutes, and then I checked temperatures on everything using a laser thermometer. The baseplate that everything was mounted to was at 78 degrees F. The driver boards both measured 88 degrees, while the scanners measured 86 degrees. Then I lifted one of the driver boards off the baseplate and placed it on a block of wood. (This significantly reduced the ability of the amp to get rid of waste heat.) After about 5 minutes, the amp had warmed up to 97 degrees, and it stayed at that temperature for the next 20 minutes. It's clear that mounting on a metal plate is sufficient to keep the amps cool, but even if you don't, they still run reasonably cool. (I would have been concerned if the temperature had gone above 110 degrees, but it never got any warmer than 97.)

The next test was to re-check the maximum scan angle with the new tuning. I measured 56 degrees, which is pretty good considering the factory spec is just 40 degrees! The new tuning obviously has more damping, which is why the scanners weren't able to scan quite as wide as before. But the image quality was excellent. Have a look at these pictures. (all are scanned at exactly 20Kpps.)

Conclusions:
The scanners perform extremely well considering their low price. ($325 as of this writing.) Even when displaying animations, there were only a few files that displayed any flicker. Otherwise the images were just as crisp as if they were being displayed on my DT-40 scanners! Cooling is excellent; there's no need to add a fan or additional heat sinks. Bolting the amps to the optical table is more then enough to keep them cool. Mirror performance is good; within a few percent of scanners costing twice as much.

Now, if you want to display very complex graphics and/or animations, you *will* notice some flicker with these scanners. But for most of the files I tried, there wasn't any flicker at all. Based on that, I would say that these scanners are an excellent first choice for a hobbyist on a budget. They are more than fast enough for beamshows, and with the wide scan angle the beamshows will look even more impressive. They will also do quite well with most graphics shows. The slight flicker you'll see when displaying complex frames is a small price to pay for saving nearly 50% of the cost of a set of 30K scanners.

The only problem I see is that you *really* need to tune these units carefully if you want to get the best performance out of them. In all I probably spent nearly 3 hours tuning them, and while I was very pleased with the results, I realize that not everyone has the patience to do that.

Adam

PS: If you're wondering what happened to these scanners - Dave and Aijii decided to DONATE them to SELEM 2007 as a door prize. Allthatwhichis was the lucky winner of these scanners. He let me borrow them after SELEM so I could re-do the review.

[allthatwhichis]

Nice Review Adam! Those images look much better after tuning the scanners. Did you watch any shows with them before the trade? When I had them I was very impressed with the quality they played beam shows, especially for the price.

[carmangary]

Looking forward to hearing more about your method of tuning. I'd like to give it a try. Could you post a picture of the quad ILDA file you displayed? Would it be possible to actually get a copy of the ILDA file or is it copyrighted and top secret?

[Laser Ben]

Wow.... Nice review! My scanners look like shit compared to those! The circle in the test pattern looks looks a spiral! I haven't tried adjusting anything yet besides attempting to tweak the pots 1/4 turn. None of which helped at all!

[marconi]

Wow, Those work pretty good for the money

Nice review Adam !

[p1t8ull]

Cool review Adam, they look pretty good scanners for the money.

[buffo]

Thanks for the kind words guys!

Aaron: I watched a couple shows, and even played a few games of Asteroids! I shot some video of that, but considering that the scanners were running at 20kpps (roughly 20 frames per second), while the video camera was shooing at 30 frames per second, and the video digitizer on the computer was sampling at 15 frames per second, well - you can pretty much guess how the video turned out. It looked like crap. Lots of flicker. The stink of it is that the flicker was *induced* by the different frame rates involved. To the human eye everything looked great - even Asteroids!

Carmangary: It's not my tuning method, it's Bill Benner's. He's been tuning galvos at our "Laser Enthusiast Meetings" for some time now, and I finally sat down and paid attention when he did it. I shot some video of the process, and so did Aaron. I'm hoping to get his footage sometime this week so I can edit it together with mine and put together a tutorial video showing how to tune your scanners.

Now, I should point out that Bill managed to tune a set of scanners in about 30 minutes, all while talking to the camera about the process and answering questions from the guys that were standing around. On the other hand, it took me 3 freakin' hours to accomplish the same thing, and this was in the middle of the night when no one else was around to distract me. It's tedious work...

Anyway, to answer your question, the square wave quadrature file looks like this when displayed:



The starburst effect at the corners is an artifact of the digital camera. All you really want to see are 4 very bright dots connected by 4 straight lines. As you increase the servo gain, the straight lines will overshoot the dots. You add low frequency damping to bring the overshoot back in-line. Eventually you'll start to get a little undershoot before the dot. (It looks like the line is tracing back on itself some.) You add high frequency damping to bring that back into line. From time to time you need to switch over to the ILDA test pattern and see how the circle looks. When you get close, you switch to the ILDA test pattern and finish tuning from there. (Though, admittedly, once I'm close I usually flip back and fourth between the square wave quadrature pattern, the ILDA test pattern, the Lasermedia test pattern, and the one with 8 triangles - not sure what it's called.)

EDIT: I had the file attached, but it didn't work. I forgot that with my Intro board I can't save frames in anything other than the new Pangolin file format. (I don't have Save as ILDA as an option.) So there's no point in attaching the frame file. You can't open it. I deleted the file to save space on the server.

The original files are in the old .ldb format, but when I try to load them with any other software they don't work right. When I get some time I'll see if I can load them up on my old QM-32 system and then save the resulting file as ILDA.

Adam

[carmangary]

Is it possible to attach them as ILDA files instead of LDS?

[buffo]

Oh hell. I screwed up. Let me fix that...

EDIT - well, it looks like I can't fix it, at least not right away. When I get some time I'll use my older QM-32 to try to get you a copy of that quadrature square wave file. (Unless someone else with a pro board can upload it in the mean time...)

Adam

[allthatwhichis]

If we are allowed, I'll attach it when I get home. It may be on the FTP already.

Adam... I mailed the drive today. I switched schedules last week and the transition has been hectic. Is it the kpps/video FPS/and human eye that makes taking video of graphics so hard to do well?

When's the 30K review getting posted?