Servo writer
Write LMR with a laser
Time to build:
10 hours
- Actuators / output devices: 2 servos
- Control method: picaxe 18x - axe31 servo driver
- Power source: bench supply
- Target environment: dark
Description:
Been playing with my new servos and servo controller, now I just need to find my sisters dog........
go here if the video doesn't work http://video.google.com/videoplay?docid=-2204066164988497414
some night photos:
Absolutely brilliant!
Absolutely brilliant!
Hey - You could have the Picaxe turn the laser on / off, and only have it write each letter once! Then it would be magnificent as well!
omg: it's another musical bot!
Did you think about a DVD
Did you think about a DVD bruner laser diode ?
Because these things are really powerful, with that you could litteraly write on a sheet of paper (or a dog) by burning it.
Here's an instructable about it :
http://www.instructables.com/id/Laser-Flashlight-Hack!!/
Marvellous
Excellent.
I had thought the servos wouldn't have enough resolution to do this over a distance. Howfar are you from the wall there?
For the mark 2, how about you replace the servos with solenoids? They should be fast enough that the image would appear to stay on the wall and you wouldn't need an open-shutter camera to see it!
Could you move the "beam" faster if, rather than moving the whole laser, you pointed it at a couple of mirrors and just had the mirrors wiggled by servos?
I just thought of another use for it: a cat exerciser. Our cat would love this. Stupid animal would chase the red dot around the wall all day. You could make your millions with this.
The board is only about 50cm
The board is only about 50cm away, it actually worked better when I pointed it at the ceiling.
The open shutter photography, I took that picture at about 11am, too much light around, so I had to make it repeat, I'll try again tonight in the dark.
Solenoids would be cool, but it was just that I was trying to figure out the servo driver, don't even need the servo driver to do it, could have been straight from the axe.
Answer: 18 servo's, what are you talking about BOA? (;
18 Servos and Two Speakers
Who mentioned anything about 18 servos?
Speakers. It seems the answer is speakers. Drive the speakers through a FET and glue mirrors onto the cones. Ooooh, yeah.
deja lissajous ?
Isn't the speaker hack only usable if you alphabet was carved out of lissajous curves?
Or do you mean to switch the laser light on/off in a timed/synchronized fashion, while the "cursor" follows a predestined and very predictable, feedback producing lissajous?
BTW, did I mention I love the Ant's project here?! Well, I do!
8ik
Hard Sums
speaker as solenoid, hmmm...
hmmm, OK I'm with you on solenoid. Must be controlled proportionally. Meaning that the MCU must be able to tell the mirror to turn so many degrees. The speaker responds to voltage. More voltage, more travel of the cone, more turn.
Cannot use pwm for the proportional control, or we'd be making music (albeit dog music perhaps). So analogue outputs from the MCU. We need drivers for the solenoids, with all the usual back emf protection. Without a feedback loop, we'd need a very precise calibration of degrees turn per volt.
I am considering replacing only the y-axis servo with a solenoided mirror. The x-axis could still be a (slower) servo, scanning the wall left to right as the writer is producing a single line of text.
Some numbers. For the illusion that the one-line-of-text is staying on the wall (persistence of vision), we would like at least 1 update of the entire image per second. The servo can sweep x over some 60 degrees in much shorter times.
Let's assume a dot-matrix style writer. For a dotted typeface we need the y actuator to splash at least eight laser dots on the wall every time it scans vertically. Each character might be six dots wide. Make it eight for character spacing. So a full line letsmakerobots.com we need some 20 characters = 160 dots(x) and a total of 1280 dots in the whole image. That means the laser must be controlled to flash on/off at 1280 times per second or better. And the solenoid/speaker must be driven from top to bottom (or vv) 160 times per second, 320 if we are too stupid to program it to write on the vice versa swoop.
Of course, just "LMR" would much simpler and like Ant's writer, could be done using a pen stroke kind of writing strategy.
Slightly related crazy idea sketch here.
but (on simple LMR)
But the pen drawing style is more complicated because it requires the x-axis actuator to sweep back every now and again. In this case in the letter R (two sweeps negative x). That changes the requirement for that actuator considerably.
I would think. (Still without my lab. Ordering shiploads of components as we speak.)
speaking of which... [link]
Hacked Gadgets sneekily drilled a hole in my head an filled it up with all these ramblings.
video
Hybrid
current v voltage
you're right about the drive
But now I am entering a shady realm. Would a different kind of drive change the kind of driver (much)?
Music
I never thought of driving the speakers with MUSIC! That is cool!
I like the idea of using a right regular polygon as a mirror. With a hexagon, suddenly you have 6x the resolution.
pluz zaw tooz zcan
It has the added bonus of giving you a saw tooth function. As opposed to all those well rounded (maybe not so) harmonics the competitor is selling.
8ik
"I had thought the servos
"I had thought the servos wouldn't have enough resolution to do this over a distance"
If the diode of the laser is behind or at the axle of the servo, you will have plenty of resolution. Same goes for a mirror; If it is placed just at the axle, or behind, you will be amazed how much resolution you can get out of a servo :)
Same page?
We may be crossing wires. If you turn the stepper through 1 degree, the laser turns through 1 degree regardless how far it is from the axis.
With what accuracy can a picaxe position a servo?
How may "counts" are there for a full 180 degrees?
Is there any noticable difference between position 50 and position 51, for example?
increasing resolution
New proposal: increase the angular resolution over a very tiny angle by dividing the 60 deg turn of the servo using a lever and a cam. 1000words.png:
The mirror would be mounted flexible, turning at one edge (the pivot). A spring or elastic band (not in picture) would force it back to its origin at 0 degrees. The servo horn would push the mirror out of its origin. Depending on the shape of the horn/cam and the distance to the pivot, it would easily reduce the resulting angle by a factor of ten. Increasing controllable resolution by as much.
The laser beam is drawn in red. The horizontal line is just an aid (angle dissector).
8ik
If you put your laser on a
(To Boa:)
If you put your laser on a stick on the servo, a long one, and let it shine towards the axle, not away.. Then the dot 1cm away from the wole thing is only traveling say 5 CM when the servo goes from 100 to 200 out of its max 75 to 225. (High resolution)
If, however, you let the laser point away from the axle, it could travel some 500 CM's for the same steps with the servo (Low resolution)
I know it's tricky & arty, but it's true :)
OOOHHHHHHH
You mean the stick is an extension of the shaft? Not an extra wide/long servo horn?
And the laser is sitting at the end of this boom, like a mic on a boom. And the laser is drooping. Chin on chest kind of thing?
Is this enough arts-speak?
but
Linear vs Rotational
If your screen is 1m in front of your axis and your laser is right at the axis, then 1 degree of rotation moves your dot a certain amount on the sceen. If you put your laser 100 miles behind the axis, then 1 degree of rotation gives you exactly the same amount of movement on the screen.
Linear resolution has no bearing here. We're concerned with rotational resolution. No matter how far back I move the laser, the height of the dot on the screen will never change.
I'm convinced we're not talking about the same thing!
unless you are drawing the axis in the wrong plane
I think Frits is extending his axis with a stick and pointing is AT the screen. Mounting the laser slightly out of alignment with the axis.
But then, why would he use a really long stick? Time to go to bed!
1 degree is always 1 degree,
1 degree is always 1 degree, yes :)
However, if you would look at this as 1 step instead - which it really is, when drawing with a laser..
Then what maters is nothowmany degrees, but how long a line, you see.
if you make one setup, it will take 5 such steps to draw 10 cenimeters.
If yu make another setup, it will take 100 such steps to draw same 10 centimeters.
It's arty and tricky, I know, but resolution of the same 10 centimeters can be high or low, depending on the setup :D
Nonlinear
y = d * Tan theta
where y is the height, d is the distance from the screen and theta is the servo angle.
So you have maximum resolution (minimum movement) where the laser is pointing straight at the scrren (theta = 0) and minimum resolution (maximum movement) at the edges of the screen.
That's tricky for an artist, but it doesn't answer my question: Disregarding the stick, the laser, the screen and all the techie stuff, what's the resolution of the picaxe / servo combination? How do you get a picaxe to move a servo through 1 degree? How much does a change of 1 in a basic program actually move the servo?
Phew. I just knew we were talking about two different things...!
optimizing path
Trying to think of an optimal path for the laser beam, I came up with this.
And then I realised that it is almost exactly what Ant's photo shows. Except for the nice round curve in "R". Which would be hard to program. Note that I tried to minimize the number of halt-and-turn moments. The bottom horizontal sweep could be drawn out as "thin" as possible by driving that servo to its top speed. But I kinda like it fat.
http://letsmakerobots.com/nod
Hey - I made the Picaxe turn
Hey - I made the Picaxe turn the laser on / off :D
Still.. your original version actually looks somewhat cooler :)
Here is my untouched version of your project:
More photos of my setup here :)
Brilliant
No, I'd hate that task,