Making a servo follow a potentiometer
Alphawookie
Posts: 14
Howdy folks. This is my first attempt so go easy.
I was interested in making a standard hobby servo follow the rotations of a potentiometer, but I ran into a snag. It does find the correct·position, as close as I can tell, but it's real jerky.
I started with the instructions for using photoresistors on the Boe-Bot, replacing the photoresistor with a 0-50k pot. I hooked up a standard, unmodified servo (way old, with layers of Pleocene·crud on it) to the connector on P12.
After a rude introduction to math without decimal points, I came up with the following program:
I was wondering if there was a cleaner method to arrive at the right pulse length, and why the thing is so jerky?
Any comments would be welcome, and heartily appreciated.
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Engineering is the art of doing·something well with one dollar, which any bungler can do with two after a fashion.
I was interested in making a standard hobby servo follow the rotations of a potentiometer, but I ran into a snag. It does find the correct·position, as close as I can tell, but it's real jerky.
I started with the instructions for using photoresistors on the Boe-Bot, replacing the photoresistor with a 0-50k pot. I hooked up a standard, unmodified servo (way old, with layers of Pleocene·crud on it) to the connector on P12.
After a rude introduction to math without decimal points, I came up with the following program:
'Robotics with the Boe Bot - LinkPotToServo.bs2
'Link potentiometer circiut connected to P6
'to unmodified servo on P12
'220 ohm resistor
'#103 cap (0.01F)
'0-50k Potentiometer
'Airtronics 34631 Servo
'{$stamp BS2}
'{$Pbasic 2.5}
'Full Left on pot TimeP6= 0.00364
'90 Left on pot TimeP6= 0.00360
'Center on pot TimeP6= 0.00200
'90 Right on pot TimeP6= 0.00052
'Full right on pot TimeP6= 0.00049
Leftpottime CON 360
cenpottime CON 200
rightpottime CON 52
TimeP6 VAR Word 'Rctime on #103 cap.
PulseLength VAR Word 'Pulse to standard servo
Pulseadj VAR Word 'Pulse adjustment from center
' PULSOUT 12, 1250 'Full left
' PULSOUT 12, 850 'Center
' PULSOUT 12, 450 'Full right
DO
HIGH 6
PAUSE 2
RCTIME 6,1, TimeP6
Pulseadj = (1+ (ABS(Cenpottime - TimeP6)*120/(Cenpottime- rightpottime)))*32/10
IF TimeP6 > 350 THEN Pulselength = 1250
IF Timep6 > 200 AND (Timep6 < 350) THEN Pulselength = (850 + pulseadj)
IF timeP6 <= 200 THEN Pulselength = (850 - pulseadj)
IF timeP6 < 52 THEN Pulselength = 450
PULSOUT 12, PulseLength
DEBUG HOME, SDEC5 ? TimeP6
DEBUG SDEC4 ? Pulselength
DEBUG SDEC4 ? pulseadj
LOOP
I was wondering if there was a cleaner method to arrive at the right pulse length, and why the thing is so jerky?
Any comments would be welcome, and heartily appreciated.
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Engineering is the art of doing·something well with one dollar, which any bungler can do with two after a fashion.
Comments
It's still on the pile to be read. Under "teach yourself electricity and electronics", "robotics with the boe-bot", "robots for dummies", "physics", and a whole passle of other .pdf stuff I printed out at work.
I'll look it up.
"The best design is the one with the fewest original ideas"
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Engineering is the art of doing·something well with one dollar, which any bungler can do with two after a fashion.
Using a pot. for position control involves a trade-off : accuracy vs time.
If you wanted 100 steps, it'd take you 0.2 sec to measure at the high end. It kind of ties up the BS doesn't it?
Is this why the encoder was invented?
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Engineering is the art of doing·something well with one dollar, which any bungler can do with two after a fashion.
The code is for one channel:
DO
GOSUB Read_Pot
GOSUB Out-Servo
LOOP
Read_Pot:
HIGH potPin
PAUSE 1
RCTIME potPin,pos
pos = pos ** $C800 'convert to 0-250
IF pos >140 OR pos <110 THEN
pos = ((pos*/$0219)+500)MIN 500 MAX 1000 'convert to 500-750-1000
ELSE
pos = 750
ENDIF
RETURN
Out_Servo:
PULSOUT servoPin,pos
PAUSE 20
RETURN
For me the secret was converting the pot data to RC commands. If you use an ADC0831 then just convert the 0-255 to 0-250 and then
after establishing your dead zone the code becomes: pot = (pot *2)+500. My servo runs real smooth and follows in both speed and position.
What cap do you use with the 5K pot on your joystick to be read by RCTIME I am trying to do the same and when I run your code I dont get a full travel I only get about 650-750-850 out of the servo when I debug the value...I want something like 500-750-1000..
I'm using a .1 ufd. What is the range of the raw data coming from your RCTIME ? I think that I got something like 1 - 304 which I scaled to 0-250. You will probably have to play with the " pos */ $0219" expression. You can always make it come out more than 500 on the low end and more than 1000 on the upper end and then limit with MIN 500 MAX 1000. Keep in touch and let me know how you're doing.
I tried a couple different resistors to get the results down to a reasonable time frame. I need to calculated the decay time based on the math, ran out of tinker-time.
Questions:
Does the stamp stop at the rctime command in the program for the duration of the decay?
Does the number returned from rctime represent the number of cycles it takes for the decay, or the time it takes. I'm confused because I get a value of 1 for very low settings. 2 milliseconds is (I think) the lowest resolution possible. I could be wrong though. (microeconds?)
Example: If rctime returns "350" does this represent 0.35 seconds?
The integer math is still giving me fits too. I've never seen a */ before, and ** used to be how you'd raise a number to a power (3**3 = 27). I'll just have to play with it some more when I get home.
Interesting code guys. Thanks.
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Engineering is the art of doing·something well with one dollar, which any bungler can do with two after a fashion.
Just one quick question. Have you referred to the PBASIC Reference Manual or the PBASIC Help file? The reason I ask is that nearly all of your questions are answered there, in one form or another, in much more detail than we might offer here.
Regards,
Bruce Bates
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I can never seem to find the info once I've read it in the printed book. I'll try again with the books though, I'm not sure the info I'm looking for is printed somewhere in the 1000+ pages I have on my table. In particular, the units of measurement don't jive with how I percieve the thing to work.
4000 cycles per second = 0.00025 seconds/ cycle
How (when I debug the program) does the stamp generate a number like .00001 as a time for the decay?
I don't have a Pbasic reference, just the Boe-bot and Microcontroller reference. (hard copies)
I've used the Help (that's where I learned about the integer math), but it is as limited as my experience.
I may just have to break down and buy something that reads .pdf files. (agony)
Thanks
Tom
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Engineering is the art of doing·something well with one dollar, which any bungler can do with two after a fashion.
I'm HERE for ANY man who know what a hitch in his git-along is! There aren't many of us left!
What operating system are you using? What kind of computer? Do you have all available Microsoft updates installed? Which version of Adobe Acrobat Reader DID you have, and which version are you now attempting to install?
What do you mean, specifically, by "Adobe will not reinstall after all exhaustive (regisrty deletion) attempts"?
Have you used the ordinary Microsoft "ADD/REMOVE PROGRAMS" feature of the Control Panel facility? The results of that attempt?
What error message or problem(s) do you get/experiene when you attempt a re-install, regardless of any of my previous questions?
At least in THEORY Adobe Acrobat Reader is so designed, that it can and will install successfully (even) over a prior version!
Regards,
Bruce Bates
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Just an old dog trying to learn a few new tricks. They're fighting me all the way.
I'm using XP, and the problem showed up a couple days before I installed all the updates a couple (3-4) weeks ago. The work 'puters a Dell, with that funky memory, and that MAY be the problem. But it doesn't explain why the work and home 'puter's messed up. I may be under attack, but I don't think this is the result of that.
Home 'puter's a Sony, XP home, recently updated.
I tried the standard removal first then, reinstalled 6.0 pro. - - Some memory error, it's been a while I forget.
Then I did another standard "remove", and installed 5.0. no change except "error opening file" now.
Then, standard uninstall, registry deletion in all users, current user, and my profile. All gone.
Reinstalled 6.0. Still no go. Another removal, and registry deletion.
I went back, and put in Adobe 4.0., (reader only) No dice. remove, delete, again.
Completely puzzled, I did a "system restore" to undo to a time a few weeks before I noticed the problem. (3 months)
Adobe 6.0 came back as expected, but still will crash just after giving me a glimpse of the document.
"error opening file" or "error writing file".
At work, I called the tech support guys in; they did the same procedures with the same result. I gave up at home. I may buy a Pentium (a bit faster than the stamp, but not much) just for adobe, but that'd be a hassle.
To add insult to injury, last night someone hacked my e-mail, and had it forwarded to another address.
They then proceeded to change my passwords to ebay, pay-pal, etc. and ordered up thousands of bucks in electronics, all to be shipped to Nigeria. They ruined my "good name".
I love computers.
Tom
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Engineering is the art of doing·something well with one dollar, which any bungler can do with two after a fashion.
It sounds to me like a good virus cleaning is in order, before you do anything else!
Regards,
Bruce Bates
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