Controlling servo with potentiometer program?

Lynxmotion Electronics & Software
1

Hello, i have a joystick that has two pots that rotate. i’ve connected the pots to the Bot Board II and i’m having trouble getting a program to move a servo porportionally. I’ve tested the values of the pots and they are 540 to 799. I’ve tried setting a servo position to the pot variable but had no luck. Any suggestions?

Bane

2

We are going to need schematics and your code. Explain how you tested the pots. What are the values 540 and 799? Ohms, variable values?

3

those values are what i got then i debuged this program (variable values)
(I just tested the code out again and i’m getting a variable value of 6 to 225)
Heres a pic of sch.
societyofrobots.com/robotforum/index.php?action=dlattach;topic=4054.0;attach=1583;image

[code]xpotvariable var byte
ypotvariable var byte

loopit:
adin ax0,1,ad_ron,xpotvariable
adin ax1,1,ad_ron,ypotvariable
DEBUG [dec xpotvariable, 19]
DEBUG [dec ypotvariable, 19]
PAUSE 1000
goto loopit[/code]
ps (is there anyway to post a image from my desktop?)

bane

4

any suggestions?

could i use some part of the program used here;
lynxmotion.com/images/html/build085.htm

5

It is sort of hard to answer this as you have not stated what you have tried, nor how the servos are connected to your board. Are the plugged into your BB2 or are they connected to an ssc32?

But for now assume that you have a servo connected to pin P4 and you are getting the range 6 to 225.

An obvious starting point is to use the servo command and simply scale the values. On the atom using the servo command, I believe that the valid range for the positions is from -1200 to 1200 with 0 as the center.
So for example lets take the mid point between 6 and 225. It is pretty close to 115. Now if multiply these values by 10 we get pretty close to the full range:

So a simple test program may look somthing like:

[code]xpotvariable var byte
xservo var sword

loopit:
adin ax0,1,ad_ron,xservo
xservo = (xservo - 115) * 10
servo p4, xservo
PAUSE 1000
goto loopit[/code]

if the adin value is 6 we would calculate (6-115)*10=-1090
if the adin value is 225 we would calculate (225-115)*10 = 1100

This may not give you the total complete range, but it might be good enough to experiment with. It also may not be proportional, this depends on how proportional your pots are. you may have to do corrections to make it linear. Code could be based off of lookup tables, etc.

I hope this helps
Kurt

P.S. - I have not compiled this or tested this so your millage may differ

6

I just remembered.

I played with inputting servo positions from a pot that is on Loki’s QwikFlash controller board. The pot is read into an analog channel, and scaled in range to match the range of one of the 'bot servos. Code is in C for a PIC, so I don’t know if any of it would be useful.

But I believe you’ll want to scale the FS (full scale) range of the pot into the desired range of a servo in the same fashion.

Alan KM6VV

7

I’m connected to BB2 and using pins (for the pots) ax0 & ax1. My servo ranges are 750 to 2500 with 1500 has 0.

So could i set the xservo variable (after the equation) the pot value and put in like this.

[code]
xpotvariable var byte
xservo var sword

servoloop:
adin ax0,1,ad_ron,xservo
xservo = (xservo - 115) * 10
for counter = 1 to 10
pulsout p0, xservo
pause 10
next
goto servoloop[/code]
(let me get my atom out and try it)

8

If in your example you needed the range of 750 to 2250 with a center of 1500, you would probably want the xservo equation to look maybe something like:
xservo = 1500 + (xservo-115)*7

So at the value of 6: 737
And at 225: 2270

You may want to use the min and max functions to limit the low and high ends to the valid range for your servo. Or you might want to try the servo command which has the scaling I mentioned in the first reply.

This is always the best approach!!!

Kurt

9

[code]
xservo var byte

servoloop:
adin ax0,1,ad_ron,xservo
xservo = 1500 + (xservo-115)*7
for counter = 1 to 10
pulsout p0, xservo
pause 10
next
goto servoloop[/code]
humm, the servo just goes to its max position and stalls. I think the value is greater then 2500. (i’ll play around with the #'s)

Can you make xservo value between 750 -2500 with this^?
I’m at school right now, but i’ll look up max and min when i get home.

I’m unformilar with this command but will do some research on it. Right of hand, would it be better to use it for this?

10

:smiley: :smiley: :smiley: :smiley:
Yes this code works (after 2 hours and reading about “servo”)

[code]yservo var sword
xservo var sword

loopit:
adin ax0,1,ad_ron,yservo
adin ax1,1,ad_ron,xservo
yservo = (yservo-638)*7
xservo = (xservo-638)*7
servo p4, yservo
servo p5, xservo
pause 4
goto loopit[/code]

I know what i was doing wrong before. I debugged my pot using a byte and then made the equation so that it would make into something that used a sword :laughing: . But when i debugged it using a sword, and re-adjusted the math it worked! :smiley:

However, there is a long time between when the pot is moved and when the servo moves. (way longer than needed :imp: )
I’m going to involve my sequencer next :wink:

bane

11

Figured it out!
I read some more about the “servo command” and if you put a …, ttime variable on the end of a “servo” and ttime = 1, you can control the time of it.

:smiley: Bane