Let's Make Robots!

PIC-AIM

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:
init: 
servo 4,75
servo 5,75
main:
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.
Andrés

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...
Andrés

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Good point, birdmun! I have a parallel post in the Picaxe forum. I´ll give the technicians there some time to answer this and see if you are on the right track. 

The only thing that comes to mind, and I apologize if its already been mentioned, is that perhaps you have a stalled servo. I am into R/C Helicopters and have had that problem with my Heli's. Also, another thing, I haven't given the whole thread a read, and again, I apologize, is that if you are using Digital Servos, they are very susceptible to noise. You really need a good source of power for them. I have one Heli with nothing but all Digital and had to run a separate BEC to deal with the problem.

As part of Dan M´s suggestion, I have measured current and I can tell you that they are not stalled. Nor are they digital servos. I appreciate your input and am glad to see that there are no hard feelings after my not so happy choice of title for the video.

Cheers,

Andrés

Here are your suggestions and what I´ve found right next to them.

1.- (Dan M. and KingsJester89) Find out if either current or tension is the problem. Nope it isn´t. I have to admit that the original power supply was somehow more marginal than what I expected, so I did two things. One) I left only one servo hooked up (half the current draw) and it still shook. Two) I used a lead/acid 12VDC 4Ah battery (properly regulated) as my power source and the shake was still there. Different frequency. But still there.  By the way, I´ve added Dan`s trick to my code (MIN 75, MAX 225).

2.- (Rick100) Change the pots in the vintage joystick. I simply unplugged the joystick from the breadboard and the shake was still there.

3.- (Boriz) Add pause 100 to the code, because it was cycling faster than the refresh rate. Didn´t solve it either. 

4.- (Ignoblegnome) Add caps as described in the forum topic he linked to. Didn´t get to the shop on time. I´ll try again tomorrow.

Thanks to all who participated. Stay tuned for more updates!

Cheers,

Andrés

I have no clue then what is causing the jitter.  I have multiple picaxe chips and multiple servos, and have not experienced it.

Oh, I see you posted the code...  Maybe I could try your code and see if I get the same jitter.  I will let you know.

ADDED: Ok, I tried your code within limits: Let me explain. I did not have your input device, so I rem'd out the readadc commands and just put in fixed values. I set it to be 75, then 225, then 75 again.

When I first tried it, nothing happened. The servo did not move at all, (including no jitter) so I inserted pause 1000 in the code and then the servo moved back and forth, but still with No jitter.

I tried "servo" instead of "servopos"... --same thing, No jitter, it just went obediently from one end to the other.

 

If that is possible, I would love to see what you get, Dan!

See the added note in my post above.  No jitter.

I looked at your video again, and it is really weird.  I have no clue what the difference is...  slightly different servo, but I would think any should act the same.

I used a 28X2 chip, but which picaxe should not make a difference. I tried several different mods to the code and did not get jitter even once.

I appreciate you taking the time to do this, Dan. It is the damnedest thing. I agree. I´ll go ahead and try servo instead of servopos just for the sake of it.

In your experiment, did you use anything in between the servo and the picaxe? Maybe a servo controller like LordGG suggested? Or did you go straight from one to the other? I assume that your power supply was the one you mentioned earlier, right? The recheargeable battery packs?

Hmmm... Time to get my thinking cap out of the closet!

Thank you, sir!  

Nothing between servo and picaxe. 

EDIT:  The rechargeable batteries are on my robot; this was done on a breadboard layout, so the power supply was commercial power dropped down to 5.0 volts with the Rev-Ed breadboard supply. -- Oh, I do have extra capacitors on the breadboard power supply --about 1500 uF.  The same 5V. supply runs the picaxe and the servo.

What if you try this code?  For me, this works fine. I tried several different code combinations, first sticking to your code as exactly as I could, but this is a simple code that should test the servo/picaxe combination without any other variables.

 

init:
servo 4,75              ;This is an X2, so I used this on pin b.4
main:
;readadc 1,b1          ;rem'd out
;readadc 0,b0


b2 = 225
servopos 4,b2          ;servopos b.4,b2
pause 1000

b2= 75
servopos 4,b2          ;servopos b.4,b2
pause 2000

goto main

 

Again, I'm new to the PICAXE and some more experience person will chime in, but I think I recall reading about servo jitter caused by floating outputs (or maybe that was inputs).

Do you have any outputs/inputs floating?