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View Full Version : Laser lap counter questions


a7i20ci7y
2007.06.19, 10:10 PM
Hey guys, I'm working on a laser lap counter/timer, but I think mine's going to be a little different than most. I'm using a GE Fanuc Versamax Micro PLC to drive it. There's an HMI, but ultimately I want to make the system capable of operating without a PC supporting it (either with an LCD or SSDs).

The purpose of the project is three fold.
1) I need a lap counter and can't afford a more expensive solution
2) I need to train myself more on PLC programming, HMI, SCADA, etc for work
3) At Nekocon (www.nekocon.com) we experienced some problems with RF solutions (we think) due to the structure. Lasers are immune to such interference.

I have relay DO so I can drive full 110VAC lights for red/yellow/green and what not. The program is about as finished as I can make it without a full prototype to test on, so it's construction time.

But I do have some questions for the guys that have done this before, and none of the tutorials I've read went into detail about this specific part of the system.

How did you build your laser bridge, and how did you aim your lasers to your transistors? I suppose it's easy enough to bend the wires so the beams hit, but I don't want to have to do this every time the bridge takes a little shove. I would really like a system that I can pretty much count on being aligned as soon as I set it up. Seems like a 1/4" target across an RCP width gap could be a little small.

Anyone have some suggestions? This much is built, plus my signal lights.
http://i92.photobucket.com/albums/l11/a7i20ci7y/Projects/RC%20Lap%20Counter/DSCF0003.jpg

arch2b
2007.06.19, 10:28 PM
nice to see you working on this!

i don't know anything really about laser systems but i have read that people have made 3/4 point screw posts to adjust laser positioning. http://mini-zracer.com/forums/showthread.php?t=11057&highlight=laser+aim

bobbyz
2007.06.20, 12:36 AM
a7,

here are some thoughts i hope you find usefull as i was considering this type of system as well recently, and specifically considering the bridge and aligning the lasers w/ transistors. the bad part is i have little to no electronic skill, the good is that i work as a cabinet engineer, and have easy access to all types of scrap materials, saws, drills, etc.

my concept is to make a bridge of 3/4 material (mdf or melamine). both vertical towers would be c-shaped with one back piece and two sides rising verticall. both of the sides would get a 1/4w x 1/4d dado cut lengthwise to recieve a piece of 1/4 material which would then be able to slide up and down in the c-shaped tower. the 1/4 material would serve as the mount for the lazer pcb and transistor pcb. one longer horizontal c-shaped connector piece would connect to the top of both towers creating a bridge. the bridge would keep both towers directly accross from each other. at the bottom of each tower would be a sturdy base, approximately the same height as the racetrack siderail. hopefully this general idea makes sense so far, i know it can be tricky to see a written design in ones head :)

The more diffiacult part of this tower design is getting the center-points of each laser and corresponding transistors to be mirror images of each other when they are attached to the 1/4 piece that would slide in place. my first solution to this would be to measure the diameter of both the laser housing & transistor with a caliper. hopefully they measure out to an exact metric or standard dimension and holes could be drilled with common drill bits, and fit snuggly in place. from the pictures i assume there can be small degree of error, say close to 1/8" based on the diameter of the transistor.

my other thoughts on this are to set each tower a little bit away from the track so a wreck into the sidewall won't bump the towers. in reality i think the tower/bridge i'm describing won't move anyway, and even if it did everything would still stay lined up.

i really like your idea of no pc to support the timing program, and the whole thing running on 110v. this sounds like a great project you've got going. keep us updated.

well those are my thoughts, i hope they make sense and are of some help. maybe some actual drawn out designs would be helpful. let me know what you think.

arch2b
2007.06.20, 08:30 AM
if you can sketch your design i can model it in cad.

PaulBoth
2007.06.20, 01:09 PM
I've built up a couple of systems for myself and a local hobby shop. The laser's regardless of quality will need to be adjustable in 2 different Axis. For the hobby shop I made the system out of aluminum extrusion with each laser being mounted in a tri-angular plate. (one screw in each corner to allow for adjustment.) To hold the adjustment tight I would use fuel tubing from larger scale RC. While these systems were reliable and robust, the material was somewhat costly.

However, if you want something quick, that works well and is fairly cheap(giving up my $0.01 patent here) is building the bridge out of normal ABS piping. With a little bit of care and some decent paint, it looks pretty good.
For the vertical on the laser side you must cut a slot about 0.75" wide. Then to mount the laser, you buy the ceiling hanging brackets (U shape.) You take a flat bar the same width as the bracket, cut/drill the appropriate holes and then mount the laser diode module into the plate using some sort of JB weld. This will allow you infinite adjustment in both the X & Y axis (Z is of no concern). The only limitation is the over all height and spacing of the lasers. Because of the brackets used, you won't be able to get more than 5 cars racing together on a stock antenna. I know this is a brief description, and may not make much sense, but I'm uploaded three pics that might help.

http://www.pgl-design.com/images/bridge assembly - pvc.jpg
http://www.pgl-design.com/images/laser bracket assembly.jpg
http://www.pgl-design.com/images/timing bridge.jpg

I'll be in the US for a few days on business, but will be back by the weekend. So if you have any other questions, post them and I'll help if I can. I have everything modeled in solidworks if you want to download a viewer (I could zip it up and email it to you.)

PB

PaulBoth
2007.06.20, 01:19 PM
I'm not knocking your idea as it sounds interesting, I just want to tell you my experience with laser modules: the don't point where you think they do. This is especially true of the ones located inside the $ store variety. I've had some of them shoot as far off as 20. Unfortunately I learned this the hard way after spending the cash to get some plates laser cut to exact specifications, only to have the diode module project a beam that waas about 6" away from the target at a span of only 32"!!!!

On a happier not, I've found the laser diode modules available from Axis Laser quite reliable and still very affordable (3mw/3V for about $5 per unit) and operate at a very cool temperature. They are small in size (very similar to what's picture above) and so far have been very accurate in terms of beam pattern/alignment.

If you ever do build one of these systems, just make sure you leave lots of room for adjustment and please take pictures (As I'd love to see them.)

PB

a7,

here are some thoughts i hope you find usefull as i was considering this type of system as well recently, and specifically considering the bridge and aligning the lasers w/ transistors. the bad part is i have little to no electronic skill, the good is that i work as a cabinet engineer, and have easy access to all types of scrap materials, saws, drills, etc.

my concept is to make a bridge of 3/4 material (mdf or melamine). both vertical towers would be c-shaped with one back piece and two sides rising verticall. both of the sides would get a 1/4w x 1/4d dado cut lengthwise to recieve a piece of 1/4 material which would then be able to slide up and down in the c-shaped tower. the 1/4 material would serve as the mount for the lazer pcb and transistor pcb. one longer horizontal c-shaped connector piece would connect to the top of both towers creating a bridge. the bridge would keep both towers directly accross from each other. at the bottom of each tower would be a sturdy base, approximately the same height as the racetrack siderail. hopefully this general idea makes sense so far, i know it can be tricky to see a written design in ones head :)

The more diffiacult part of this tower design is getting the center-points of each laser and corresponding transistors to be mirror images of each other when they are attached to the 1/4 piece that would slide in place. my first solution to this would be to measure the diameter of both the laser housing & transistor with a caliper. hopefully they measure out to an exact metric or standard dimension and holes could be drilled with common drill bits, and fit snuggly in place. from the pictures i assume there can be small degree of error, say close to 1/8" based on the diameter of the transistor.

my other thoughts on this are to set each tower a little bit away from the track so a wreck into the sidewall won't bump the towers. in reality i think the tower/bridge i'm describing won't move anyway, and even if it did everything would still stay lined up.

i really like your idea of no pc to support the timing program, and the whole thing running on 110v. this sounds like a great project you've got going. keep us updated.

well those are my thoughts, i hope they make sense and are of some help. maybe some actual drawn out designs would be helpful. let me know what you think.

bobbyz
2007.06.20, 01:42 PM
pb

that's some good insight, thanks for the input. i'll send out a sketch maybe in the next week or so. soooo busy here. blah.

a7i20ci7y
2007.06.20, 02:11 PM
Got a link to Axis Lasers? Didn't find it with Google. I got my lasers from instapark, http://www.instapark.com/category/laser-products/r-laserm1.php
I might have damaged a couple of diodes though. The site says 4.5volts, but the only DC source I had handy was 5v which seemed to work fine, but one of them is dim now. So when I get home I'll just toss a resistor in series with them and switch out the diode with a spare.

I wouldn't be quite so worried about the structure and I'd just start experimenting, but money is tight so I want to get it right in as few iterations as possible. The pictures above have given me some ideas to work with though. I think I'll get some materials and stat cobbling together.

empowered
2007.06.20, 03:40 PM
hi, we made one for our track, conected to a computer, we made a metal solid arc, like the pvc draw, and the lasers where put in the metal so they cant move and no adjustments are needed, other thing, for a correct work of the lasers and phototransistors the lasers must be 1>mw (miliwatt), less than that you will have big problems whith the aligment and distance, we use 5<mw laser diodes. i hope this help you

PaulBoth
2007.06.25, 07:25 AM
Ai, that laser that is dim now was overheated (received more voltage than it as capable of handling.) It will never be as bright as it was initially. From now on it will continually get dimmer until the diode is unable to sustain light. Use it for testing, but don't hardwire it into a rig, or you'll be replacing it at a later date.

As a tip for everyone, even if your laser says it's 4.5V or whatever, always try using as low a voltage as possible. When I've used 4.5V diodes, I typically run about 3.2V or 3.3V to them. They still get bright, they just don't burn out... (think of it this way, that 4.5V is designed to be used with alkaline batteries, after 5 minutes they aren't putting out 4.5V [three in series].)

PB

a7i20ci7y
2007.06.25, 08:21 AM
Yeah, that's what I figgured. Normally they run off three button cells, but it occured to me that if their peak discharge was low, running the same voltage on beefier batteries could still burn out the diode. So anyway, I'll fix that.

I came up with a mounting option using a turn buckle. I just have to find the chuck key for my drill press... :mad: I'll post pictures once I have the hole drilled.

a7i20ci7y
2007.06.27, 10:13 PM
Okay, I got my first laser mount done. I used a 5/32" x 4 - 3/4" turnbuckle. The lasers were labeled as 1/4" but when I pressed a 1/4" hole it was a tiny bit too small. So I stepped up to 17/64" and it was slightly larger than I wanted (I guess I need a 33/128" bit). I had to glue the laser in place (solder won't grab the turnbuckle :( ). It seems quite solid though. I also found that with a 50 ohm resistor, my laser seems pretty bright and after 10 minutes of running, it was barely warm to the touch.

The idea with the turnbuckle is that I'll glue one screw to the buckle. You can twist the screw to adjust the laser up and down. The other screw you can push forward or back to adjust the laser left or right. It will be mounted inside a PVC tube with an aperture for the laser to come out of.
http://i92.photobucket.com/albums/l11/a7i20ci7y/Projects/RC%20Lap%20Counter/DSCF0006.jpg

Tuesday I took a tour of the GE Fanuc plant in Charlottesville VA where my PLC was manufactured :cool:

Spoon
2007.06.27, 10:50 PM
Tuesday I took a tour of the GE Fanuc plant in Charlottesville VA where my PLC was manufactured :cool:

You should have stopped by the Charlottesville Mini-Speedway. You only would have had to come 15 more minutes South. bnwhtlw and I setup every Tuesday night at one of the hobby shops. We run from about 6 until 8:30. We get there around 5:00 or so to setup.

a7i20ci7y
2007.06.28, 08:25 AM
Wish I could have, but I was with my boss, so no extracurricular field trips :(

I have a bunch of IO available still. Anyone have any ideas about what to do with them? I have 34 discrete in and 17 discrete relay out available. Out puts could be seven segment displays (expensive :( ), lights, motors, fans, up to 240VAC/24VDC 2A. Inputs could be buttons, switches, sensors, etc.

PaulBoth
2007.07.04, 09:31 AM
The seven segment displays would be cool if you made a position stack right next to your gantry (top 5 cars position and lap number).

Laps remaining in race, laps completed in race etc. would also be cool.

You could also make up a speed trap and display the speed of a car (useful for when only one car is on the track though) - unless you ran a second set of laser lights across the track at the same height as the main timing ones.

PB

P.s. any pictures of the system thus far?

a7i20ci7y
2007.07.09, 08:48 AM
I would need a non-relay output module to run seven segment displays. Well, technically I don't need one, but it would take 7 relay outs to drive one digit. If they were solid state I could use presistance of vision to run multiple displays off the same seven out puts and switch the common, so n displays using n+7 DO instead of n displays using n*7 DO. They make IC that do this too (ever notice that seven segment displays flicker in some systems?). I have 24 DO, and I'm using 3 for the signal lights and 4 for lasers, that leaves me 17 available outputs, so I could run two digits :( If I leave all lasers on all the time, I could use those DOs to drive a third digit.

I've hit a snag though. In the pictures you'll notice there's a resistor on the cathode side of the laser. Well, the plan was to have the lasers adjustable, so I really wanted to replace the resistor with a wire, but I can't desolder it without burning the laser. So I'm going to attach a wire to the resistor but I need to pick up some heatshrink or something to strengthen the joint a bit.

I also need to widen the slots on the horizontal adjustment side of the pipe. I kinda did a crappy job cutting the slots because I don't have routing table :( But it should suffice, just needs to be wider than I thought.

It's not much to look at, but I'll post some pictures tonight.

a7i20ci7y
2007.07.09, 10:35 PM
Well, here it is. Still need heat shrink, but I should wait till the end of the month, wife's starting a new job.

Anyway, it isn't much to look at, it's very prototype, and I'll probably end up redoing the whole thing again after this one is finished and functional.

http://i92.photobucket.com/albums/l11/a7i20ci7y/Projects/RC%20Lap%20Counter/DSCF0008.jpg

http://s92.photobucket.com/albums/l11/a7i20ci7y/Projects/RC%20Lap%20Counter/?action=view&current=DSCF0007.jpg
http://s92.photobucket.com/albums/l11/a7i20ci7y/Projects/RC%20Lap%20Counter/?action=view&current=DSCF0009.jpg
http://s92.photobucket.com/albums/l11/a7i20ci7y/Projects/RC%20Lap%20Counter/?action=view&current=DSCF0010.jpg

PaulBoth
2007.07.10, 07:43 AM
Looks good, my only concern will be the ability to minutely adjust the laser diode in the X axis. At first I was thinking you'd do the adjustment by twisting the eyelets, then I checked the other pictures and one of them shows a slot...

Hopefully it won't be an issue and the laser's you have are accurate/straight. ;)

Take a pic once it's up and operational ~ looks good so far.

PB

a7i20ci7y
2007.07.10, 07:54 AM
Yeah, I'd rather be able to turn a screw too. But to do that I'd have to thread the eye on the slot side and run a screw through that. Doable, and I might even try it, just more complicated.

a7i20ci7y
2007.10.09, 08:57 AM
Alright, too long without an update. Between work, school, wife & kid and other projects, I just haven't had time.

I've experienced unending frustration with the laser mount portion of the project and I've decided I'd best go with some other system. A little browsing about on the net has yielded this little gadget. (http://www.amazon.com/Sierra-Tools-2%252dCar-Parking-System/dp/B000LZFUAO) I've found better prices elsewhere, still hunting for lower. Anyway, I'm pretty certain I can wire around the motion sensor to run the lasers as needed. It's more expensive than other lasers, but it looks like a more robust housing than I can build. And since we have to pack up our track after every GTG, this is important.

On the other side, I placed three phototransistors in parallel to make a larger target (easier to hit). This has helped immensely.

For those of you with more money than sense, they make these. (http://www.sti.com/curtains/cudatash.htm)

PaulBoth
2007.10.23, 09:08 AM
Try hitting up your local dollar store. Some times you'll find magnetic door holders. They are a solid base with a completely loose/floating magnetic pad. You could easily mount your laser diode modules to it and it would give you nearly unlimited adjustment for laser compensation. However, you would need to purchase a small die/tap set. Basically you would drill through the base and tap the hole. You would then put in a screw to lock the laser into a fixed/known position.

Basically doing what your laser detector system is doing, but hopefully for alot less money.

PB