Planting straight rows with laser?!

[tractor1971]

I stumbled on the idea to use a laser instead of an expensive GPS system (which is too expensive for my purpose) to plant straight rows for my vegetable crop. I need a laser to shine 1000-2000 ft on a ?white sheet mounted in front of my tractor. The laser will be mounted on the other side of the field on a tripod. It must obviously be visible in daylight. Am I realistic, is it possible, or am I just out to lunch?

 

[Things]

Having a laser line visible over 2K feet in broad daylight will be a challenge. You're definitely going to need a very high powered laser. and probably green as it's the brightest to the human eye for power output.

 

[ARG]

If you're doing it in the dark it wont be hard You'll probably be looking at 500$+ for a laser like this.

 

[benmwv]

From what I can tell he isn't trying to make a line across the ground for 2000ft or have the dot visible from 2000ft away. I think he wants to have the laser pointed at him on the tractor from 2000ft away. The dot will hit a white sheet so he can try to keep it in the same spot, keeping the tractor in line.

I'd say low divergence low power green.

 

[joeyss]

I'm pretty sure a 500 mw green with a beam expander would do.

 

[Things]

Reading his post, it sounds like he wants to use a line generator to shoot a line across his field.

This will require a LOT of power to be visible in daylight, and probably cost more than a GPS system. 500mW green through a line generator won't be visible in daylight for any more than a few feet.

 

[Cyparagon]

I understood it as he'd be pointing from behind the tractor onto a sheet in front of the tractor. As he moves forward, he keeps the dot in the center of the sheet, therefore keeping the tractor in a straight line.

 

[sinner]

This can be done, but green lasers with super low divergence more likely to be expensive as joeyss said..

 

[tractor1971]

Yes, your assumption is correct, I want to keep the dot in the centre of the sheet to keep the tractor in a straight line. Look like I will have to work a few nights, I need a 100 rows of a 1000 ft long. A 5 mw will be seen at night won't it?

 

[sinner]

get a 50mW+ module just to be safe, put that module in a huge-ass heatsink to make it a labby.. That'll do at night!

 

[cheech226]

a 405nm laser and some type of florescent (prolly not the right word) paint on the sheet should work in daylight. the 405nm diodes have great beam specs.

 

[RA_pierce]

Hmm...
Perhaps you can use the laser as a guide and then use spray paint to mark points along the rows.
It may take a little longer but seems more practical than mounting the laser on the tractor. After all, I doubt the terrain is perfectly level so it will be difficult to keep the laser on target while the tractor is moving.

During the day, 100mW+ of green might be good enough to project a visible dot over 1000ft. It will be quite expensive for a good one but probably not as much as the GPS alternative. You could get away with a lower power laser if your target has some retro-reflective tape.

https://www.google.com/#q=retrorefl....,cf.osb&fp=95d8ad60d17382aa&biw=1366&bih=678

Always be careful when using lasers!

 

[tractor1971]

I was actually thinking of just shining the laser on the tractor, and not mounting it on the tractor. I will try and see what reflective tape does with laser, never tried that. Thanks again for the ideas. I hope this laserbug does not bite me, it may become an interesting/expensive hobby.

 

[RA_pierce]

I was actually thinking of just shining the laser on the tractor, and not mounting it on the tractor. I will try and see what reflective tape does with laser, never tried that. Thanks again for the ideas. I hope this laserbug does not bite me, it may become an interesting/expensive hobby.

The reflective tape will reflect a large amount of the light back toward the source (the laser). This makes the dot brighter if you are standing behind the laser. This tape works the same way as the tape around traffic cones, road signs, and other reflectors you might see on the road.

 

[nouthyella]

Actually, is the GPS solution really that expensive? What kind of precision do you need?
An iphone 4 can reach sub-10m precision easily in city areas, probably better in an open field with more satellites visible.

With a laser you have to get a good tripod/possibly a theodolite too, GPS might be the better solution especially if you already have an iphone or similar smartphone, due to the minimal opportunity cost.

 

[Benm]

I think the problem will mainly be divergence: At the far side of the field you'll be 600 meters or so from the laser, and even with a very good divergence of 1 mrad, the 'dot' would be a circle over a meter in diameter at that point.

You could still be able to see that during dusk and at night, but daytime would be problematic. A 10x beam expander can mitigate this problem, but that increases the cost of the system quite a bit ($500-$1000 or so?).


A different approach could be to use a low (1 mW) laser, and look directly into it through a sight, which can be as simple as a piece of pipe provided its straight. As long as you see the laser, you know the pipe/sight is oriented inline with the beam, and you can proceed in the direction you are going.

Looking into a laser obviously has its risks, and the most important part of it is that the laser is actually low power. At 1 mW there is no change of eye damage though, and it will probably not be overly umcomfortable either: Starting from the far side of the field it will not be that bright, and by the time you get to 50 meters from the laser or so you can drive the remainder of the distance without using the sight.