Let's Make Robots!


Remote controlled, extremely precise (yeah, right!) 2-axis laser death ray

This started out as a top secret destruction weapon to be placed on the moon with plans of taking the world hostage, in order to make a trillion dollars... (...mmm... I think I´ve seen this movie before...)... and it ended up being a laser pointer mounted on a two axis jig, made out of Futaba servos. It is controlled by a hacked, 22-year-old IBM analogue joystick.   
Now back to reality: This really started as a comment by user chench (http://letsmakerobots.com/user/5049) to a forum post of mine, (http://letsmakerobots.com/node/27588) suggesting an analogue gauge. The neuron that was handling that idea collided with another one that was taking its time to decide what to do with a spare laser pointer I have. Presto-pronto an idea was born. 
A hacked 2 axis analogue joystick going straight to 2 ADC pins. That value mathematically translated to servo values (thank´s to Chench´s formula) and the laser pointer cable-tied to the horn. Let´s not forget the bracket I improvised to attach on servo to the other.
I am using a Picaxe 18X and here´s the code:
servo 4,75
servo 5,75
readadc 1,b1
readadc 0,b0
let b2=b0/2+75
let b3=b1/2+75
servopos 4,b2
servopos 5,b3
goto main
The problem I´m having (take a look at the video) is that of servo jitter. As fas as I can tell, it is caused by the instability of the ADC reading coming from the joystick, even when I don´t touch it. I have gone though many posts in the Picaxe forum trying to find a solution, with no real luck. The best I can think of, is writing code to round up the values. According to the debug screen, my instability is smaller than value 5 (inside of the 0-255 range).
 Any ideas, community? H-E-L-P!

UPDATE (July 25th, 2011)
Finally I have been able to integrate the new 3A power supply to the old experiment and the jitter is more under control than before. See secong video near the top. Next step is to tie down all unused inputs and change the pots in the joystick as suggested by many "colleagues" in the forum.
Thanks to all!

UPDATE (July 26th, 2011)
At this point, and after today´s experiments, I believe it is safe to say that I have tried out every suggestion posted here and on the Picaxe forum. "We" have managed to reduce the jitter an awful lot, but it is still there. Take a look at the third video uploaded. Here´s an unofficial list of everything I´ve tried, hoping that it will be useful to someone else who decides to go this route.
  • I´ve run the servos and the logic from the same power supply and from different ones. The last one I´ve used for the servos alone was 3A properly regulated.
  • I have made sure that, if using 2 PS, that the GNDs were common.
  • I have switched the pots from the hacked joystick from 100KΩ to brand new and noiseless 10KΩ.
  • I have tied all unused inputs from the Picaxe down via 10KΩ resistors.
  • I have tried to implement filtering in the code.
...and none of this has truly solved the problem.
The jitter has diminished considerably... but it is still there. I don´t think it is going to get any better than this, so I´ll move on to other things.

I want to express my most heartfelt gratitude to all those who took the time to read the thread and chime in ideas.

UPDATE (Sep 4th, 2011)
Down in the commentary section, Dan M. (among others) suggested trying servopos commands on their own, isolating them from the readadc commands. I has taken me a while, but finally I got around to trying it out. This is in the context of another experiment. However all the boards and servos are exactly the same as the PIC-AIM project, with the exception of the joystick. 
The idea come to me while watching one of Chris the Carpenter´s recent videos, a quick demo on a GGBot. That particular bot, while asleep, has the PING))) sensor looking straight down. When you wake it up, the turret tilts up for distance sensing in autonomous mode. I don´t know if that is only for personality sake or not. However, I thought that it would look cool to have just one (Sharp, in this case) sensor to determine distance and to make sure that there is floor ahead of the robot. You can watch what I have come up with in the last video uploaded.
With this experiment, it becomes obvious that the hardware is not the problem. I can also discard the joystick as a source of jitter, because I´ve changed all the pots in it. Conclusion: I don´t think my approach can be built like I wanted, at least not without the addition of a servo controller, like LordGG suggested in the comments. 

UPDATE (Sep 17th, 2011)
For some reason this project of Rick100 came to mind today. I reread his post and downloaded his code for the Picaxe 08M and found what could be the solution to my problem. I quote a bit of his code:
'couldnt use servo and servopos commands because of jitter
'used pulseout for servo pulses and pause commands adjusted with oscope to get close on timing
I will try to adapt his approach for my project tonight.
I´ll keep you guys posted.

UPDATE (Mar 18th, 2012)
SUCCESS, finally! I admit this has taken longer than anticipated, but you see, in between I started a company and got married, so I´m sure everyone will understand. The first video from the top shows the laser death ray in action.
I guess the only thing left now, is to figure out a way to get it to the moon so I can fulfil my plan of taking the world hostage, in order to make a trillion dollars...

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At this point I could benefit from a schematic of a PSU for 6VDC servos. One trusted by any of you. Thanks.

4xAA completly fresh?

Check mate! (insert embarrased smiley here)

Forgot to share this other one, with you all:

This is what happen to the servo train of pulses when the PIC shares the PSU with the servos!

I just LOVE this oscilloscope!


You could try oversampling to get rid of the ADC-Noise. Just add up 5 readings and then divide it by 5. Maybe you'll Be able to fix your problem.



Hey torrentula,

Thanks for the input. I had given that a try after a comment by user Gabriel_f. Unfortunately that didn´t solve the problem successfully.


I am not sure if there is still space left for another payload, but you coulod talk to MarkusB when he shoots his rocket to the moon.

Big thumbs up to Lumi! ;)