2.8 laser woes...(alignment keeps going off)


#1

Finally getting ready to start putting my 2.8 to use…and would love to get my lasers lined up correctly…

Followed the instructions in the build when I first mounted them, got them 10cm apart, glued them in and left it overnight. I did not however test the spacing with the e-tube installed, and when I put it all together the next day, the lasers were off.

So I left it for a while and went on to getting it up and running correctly.

Finally went back a couple weeks ago and managed to break the lasers free from the glue so I could readjust them.
This time I checked them with and without the e-tube, and they were exactly 10cm apart from 3’ away to about 15’ away…which would lead one to believe that they were parallel.
So I went ahead and glued them down and let it sit overnight…Only to fire it up the next day and once again discover that the alignment had gone way off! So much so that the lasers actually crossed over at about 8’
So how in the heck are you guys actually getting these things lined up correctly? I’m using the camera upgrade chassis.


#2

Hi Geoffrey:

I’ve had this problem as well, although not as bad as you describe here.

I wonder if part of the problem is that the lasers that come with the kit are not really designed to be precision pointing instruments. IIRC the kit comes with a spare laser- if you take it apart you’ll probably find that its a small PC board floating inside the brass housing. I’ve always wondered if things would be improved if that board was staked down inside the brass housing, rather than free-floating. It’s an experiment that I’d like to do sometime, but unfortunately there are plenty of things in the queue ahead of this, both for Trident and for my homemade ROVs.

We’ve started talking about a laser scaler option for Trident. It will likely use a periscope optical design that guarantees the parallelism of the beams. Unfortunately that will drive up the cost somewhat, but few good things in life come free…

-W


#3

Hm, so if I got the laser focused, and then filled the housing with a small
amount of epoxy or CA somehow…that might solve the issue.
Would that cause any other problem internally with the lasers?


#4

I don’t know what would happen if you got epoxy up onto the laser chip itself. I was thinking more along the lines of tacking the back side of the board with a couple of globs of 5-minute epoxy.

Laser diodes are cheap on Amazon/E-bay. You might want to get a couple to experiment with, and try a couple different methods of epoxying to see what works best.

-W


#5

Walt, As a suggestion for laser distance, why not use three lasers? Make the outside ones parallel for side to side measurements and a third laser mounted at a higher point between the two outside. At a preset distance, the three would be in a straight line. Shorter than the set distance the middle laser would be above the center line and further than the set point the middle one would be below the center line. Pre-measuring the offset would let you calculate the distance.


#6

Hi Jim:

Interesting idea. If you give it a try, let us know how well it works.

Given the pace at which image processing and cameras are improving, I suspect that software plugins that do range measurement are going to work well. If you have stable light sources and a stable field-of-view for the camera, software can do the rest with surprising accuracy.

-W


#7

It would appear I’m my own worst enemy…to keep them from moving this time I really piled the CA on there…and now of course I can’t get them out. According to the chemical resistance sheet, acetone isn’t a good idea, so short of crushing the diode out of the mount, any suggestions on how to remove them?