Problem with Servo Control (PSC)

skatj · 2008-01-18 04:13

My PSC (serial) just came in the mail and I managed to get to the stage where the LED is actually lit (which is a tremendous feat for me), so I tried the source code from the Parallax PDF page.

' {$STAMP BS2} 
'{$PBASIC 2.5}
ch VAR Byte
pw VAR Word
ra VAR Byte
Sdat CON 15
baud CON 396
ra = 7
ch = 11
DO
pw = 1250
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
PAUSE 1000
pw = 250
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
PAUSE

I copied and pasted it exactly as is, and it goes to the same positon each time, no matter what numbers I put in for pw or ra. Can someone explain to me in simpler terms exactly what variable does to control a servo.

Thanks

Zoot · 2008-01-18 10:48

Your code looks OK, but I don't think you posted all of it (your DO has no LOOP and your last pause has no parameter, which shouldn't tokenize and download to the Stamp).

pw is a Word -- two bytes (the two halves of the world are sent as pw.LOWBYTE and pw.HIGHBYTE). The PSC uses 2us units, so pw=750 = 1500us or centered.

If your servo always goes to the "same position" what position is that? Centered? If so, is the servo plugged into servo port 11?

Do you have adequate power to both the PSC servo V+ terminal block and separate power for the Stamp? Do you have the PSC plugged in to PIN 15 of the Stamp? When your program runs you should see the green activity light on the PSC flicker rapidly? (It does this when receiving serial data.)

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skatj · 2008-01-18 17:48

I left it out during the copy/paste.

'{$PBASIC 2.5}
ch VAR Byte
pw VAR Word
ra VAR Byte
Sdat CON 15
baud CON 396
ra = 7
ch = 11
DO
pw = 1250
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
PAUSE 1000
pw = 250
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
PAUSE 1000
LOOP

I double checked that servos were connected to the right port, as well as the PSC. I am using 4 AA batteries to power the PSC separately and a 9V battery for the stamp. I also see green activity light when the program is running.

I tied a rubber band to the left-most horn when I turned it as left as I could, and each time it moves to the position that is 90 degrees right of it. (The next horn over's position). No matter what numbers I put in or wherever I start it from, the horn will always go in that position.

Zoot · 2008-01-18 21:22

So if you try running this code, and if you enter 750 into the debug terminal, and then after that enter 1800, you don't get the servo moving?

'{$PBASIC 2.5}
ch VAR Byte
pw VAR Word
ra VAR Byte
Sdat CON 15
baud CON 396
ra = 7
ch = 11
DO
DEBUG CLS, "Enter servo position in microseconds (500-1500-2500):"
DEBUGIN DEC pw
pw = pw/2 MIN 250 MAX 1250
DEBUG CR, "Sending actual servo value: ", DEC pw
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
PAUSE 1000
LOOP

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skatj · 2008-01-19 03:41

Nope, I can't get it to move. I double checked all the wiring/channels/etc and it's correct.

also, I forgot to say but there's a green light (flickers a couple times for about 1 sec)

Post Edited (skatj) : 1/19/2008 3:46:34 AM GMT

Zoot · 2008-01-19 03:46

Can you post a photo of your setup?

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skatj · 2008-01-19 04:01

I only have a webcam, so the quality's really bad. Tried to fix it up with photoshop a little bit.

http://i137.photobucket.com/albums/q224/skatj/servosetup.jpg

(ignore the stuff on the breadboard)

Zoot · 2008-01-19 04:27

Well, if you ran either your code or my code, I wouldn't expect to see motion on either servo:

a) it sure looks like you have your servos plugged in to channels 14 and 15; the code sends changes to channel 11

b) code only does one servo (11)

In the PSC command, the ch var is the "channel" servo number 0 - 15 ON THE PSC.

So... if the photo is accurate, try this. I'm getting rid of most variables, so you can hopefully see some results.

'{$PBASIC 2.5}
Sdat CON 15
baud CON 396

servoPos VAR Word

DO

servoPos = 500
' after the !SC, 14 is the servo channel (on the PSC), 3 is the ramp (speed), then the position
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 14, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 1000
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 14, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 500
' after the !SC, 15 is the servo channel (on the PSC), 3 is the ramp (speed), then the position
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 1000
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

LOOP

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skatj · 2008-01-19 05:04

Nope, I changed the ch in your code to 15 for each time I ran any source code, even before I posted this thread =(

Zoot · 2008-01-19 05:27

OK --

1. Would you post the *exact* code and a picture of *exactly* the setup you have when you run that same code? That way we can at least baseline it.

2. How are you getting power to the servos -- it looks like you connect the power leads from the AA battery holder into one of the servo cables?

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skatj · 2008-01-19 05:37

I used your code (the one where you input a pulse), and tried both channels 14 and 15. I didn't change anything apart from those two digits. I took the photo of my setup shortly afterwards. Unfortunately I don't think I can get one of better quality, especially since it is night now where I am, so the lighting will be awful.

I hooked up a battery holder with 4 AA batteries (1.5V each), to the positive and negative terminals of the PSC.

edit: I tried the last code you posted, with the exact same setup. Both servos moved this time (expectedly), but to the same position as I described before. It seems like the connections and everything are in working order but I dunno..

also, I don't know if this is significant, but the servos are locked in place while the PSC is on, I can't move the horn with my mind or anything, but then again that might be normal.

Post Edited (skatj) : 1/19/2008 5:44:47 AM GMT

Zoot · 2008-01-19 07:51

Somebody said...
but the servos are locked in place while the PSC is on, I can't move the horn with my mind or anything, but then again that might be normal.

Yes -- that's normal -- these are motors with circuitry to move them to the position set by the pulsewidth they receive, and they are always trying to maintain their position -- the PSC will always keep sending whatever pulsewidth (position) it was last told to send on that channel. On reset it sends 1.5ms (centered) position to all servos.

Unclear from your last post if it's working or not? My code should send each servo to 1ms then 2ms, in turn. Then back again, over and over. On most servos 1ms to 2ms would be about 45 degrees from center in one direction, then 45 degrees past center in the other direction.

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skatj · 2008-01-19 08:20

No =( It still has the original problem in that anything I do moves the servo to the same position each time, and won't go anywhere else.

Unsoundcode · 2008-01-19 16:21

Is the red LED lit

Did you check your communication set up with the version instruction, the code is in the PSC document.

Did you remove the jumper that sets the channels from 0-15 to 16-31.

If the above is OK try a fresh set of AA's for the servos remove one of the servos and just try and get one to work. Although you are providing power to the servos through one of the channel pins, which is fine, the PSC is designed to have the servo power connected via the small blue screw connector, but you may have a reason why you would rather use a channel connector.

If you get past the above checklist Zoot's code should work

Jeff T.

skatj · 2008-01-19 19:50

1. Red LED is lit.

2. I ran the code from the PSC document, if that's what you're talking about, my firmware version is 1.4

3. Which jumper is this? I have the red/black/white cable plugged into the left port, not the right one, but I dunno if that's what you're talking about.

4. I have the battery pack soldered onto the pins under the blue screw connectors. The batteries are fresh out of the box.

Okay, this time I tried using just one servo on channel 15. I used Zoot's code, changing 14 to 15.

' {$STAMP BS2}
'{$PBASIC 2.5}

Sdat CON 15
baud CON 396

servoPos VAR Word

DO

servoPos = 500
' after the !SC, 14 is the servo channel (on the PSC), 3 is the ramp (speed), then the position
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 1000
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 500
' after the !SC, 15 is the servo channel (on the PSC), 3 is the ramp (speed), then the position
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 1000
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

LOOP

What happened was, for some reason this time I could move the servo easily with my hand (although there was some resistance). When I started the program, the servo moved to the same position as before (the only one that it would move to), and every time I moved the horn away from that position, it would go back to where it was. Any reason why it's behaving differently today? I didn't change anything.

Speaking as someone who has no idea how servo pulse control works, it seems like the signals are reaching the servo controller, but something's causing it to interpret every signal as the same position each time.

Post Edited (skatj) : 1/19/2008 7:57:44 PM GMT

Unsoundcode · 2008-01-19 21:44

Hi skatj, the jumper joins two pins that are sticking up from the PSC circuit board on the right side of the large capacitor and above the "Inc" of Parallax Inc. It will likely be a blue or black small piece of plastic that you can remove with your fingers or a pair of tweezers. The jumper should be removed to use the channels 0 to 15. I'm at a loss to think what else the problem could be, your connections look good and you have already established that the comms are good.

Jeff T.

EDIT: I know you have this covered but I have to say make sure SW1 of the PSC is in the on position

Post Edited (Unsoundcode) : 1/19/2008 10:01:14 PM GMT

Zoot · 2008-01-19 23:23

Baffling. Your servos have power, or they wouldn't turn. I would not try to turn a servo horn, though, on a servo that's "under power".

The jumper unsoundcode is referring to will make the PSC answer to channels 16-31 instead of 0-15. If it's not installed, fine. But I do suggest you read the PSC documentation which discusses the jumper and so forth.

You soldered leads to the terminal for power? Any reason not to just use the terminal block?

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
When the going gets weird, the weird turn pro. -- HST

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skatj · 2008-01-19 23:24

I removed the jumper but nothing happened. If by 'SW1' you mean the off and on switch then yea that's on.

I dunno if this is worth mentioning but when I move the servo horn out of its place and it goes back to its original position, the green LED doesn't flicker. It only flickers when it actually sends the pulse (I removed the do/loop from the above program to verify), but I don't know if that's normal behavior.

Thanks for the help though guys, maybe I got a defective one or something =/

zoot said...
Baffling. Your servos have power, or they wouldn't turn. I would not try to turn a servo horn, though, on a servo that's "under power".

The jumper unsoundcode is referring to will make the PSC answer to channels 16-31 instead of 0-15. If it's not installed, fine. But I do suggest you read the PSC documentation which discusses the jumper and so forth.

You soldered leads to the terminal for power? Any reason not to just use the terminal block?

To be honest, I wouldn't know how else to connect the battery pack wires. What plugs into that square opening in the blue terminal?

Post Edited (skatj) : 1/19/2008 11:31:44 PM GMT

Zoot · 2008-01-19 23:35

The green light blinks during serial activity (when your stamp is sending data via SEROUT to the PSC).

The blue terminal block lets you insert wires and tighten them down with the screws on top.

Now, I think there *is* something funky going on here, because your setup basically looks OK, BUT I STRONGLY advise you to read through the PSC manual *carefully*. It has wiring diagram for terminal block, explains the jumper, etc.

Additionally, you might want to download and check out "Robotics with the Boe-bot" and read the chapter on servo control -- it's a great a explanation of what servos are, how they work, and how to control them with microcontrollers.

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skatj · 2008-01-20 01:35

This is the manual you're talking about right? http://www.parallax.com/Portals/0/Downloads/docs/prod/motors/ServoControllerManualRevBv2_4.pdf
I didn't see anything about the wiring other than the picture with two wires going into terminals (which didn't really show whether it went under or in it), same with the jumper.

Anyway I'll keep trying.. and I'll definitely read through the servo control chapter. Thanks guys.

Unsoundcode · 2008-01-20 01:54

Yes thats the document, the jumper is mentioned on page 5. If the jumper was in place initially that would explain why the PSC did not work at first.

Strip back about 1/4 inch of the insulation of the servo battery leads, push them firmly in the blue connectors then tighten with a small screwdriver. As you look down from the top the red positive wire should be in the right hand terminal and the black negative lead in the left.

The servo channel numbers·are printed on the PSC board against their respective pins, they might be difficult to line up at first so just double check you have the motor connector in the channel that matches your code.

Jeff T.

skatj · 2008-01-20 02:28

Thanks Jeff, should I rewire the power source, or does that not matter?

Unsoundcode · 2008-01-20 02:32

Personally I would, it makes it easier to disassemble plus thats the way it's designed anyway. But if you feel the power supply is wired correctly and securely and you are happy with it then it's up to you.

Jeff T.

Zoot · 2008-01-20 02:32

Ditto. Terminal blocks are meant for poking power wires into and (and removing).

This code will cycle through all 15 channels. It will take ~32 seconds to go through the whole thing.

' {$STAMP BS2}
'{$PBASIC 2.5}

Sdat CON 15
Baud CON 396

i VAR Nib
servoPos VAR Word

DO

FOR i = 0 TO 15

servoPos = 500
' after the !SC, i is the servo channel (on the PSC), 2 is the ramp (speed), then the position
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", i, 2,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 1000

servoPos = 1000
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", i, 2,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 1000

NEXT

LOOP

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Post Edited (Zoot) : 1/20/2008 2:38:06 AM GMT

skatj · 2008-01-20 03:15

Ugh, alright, so I tried plugging the PSC into a different servo port on the BOE, 12. I tried this code that you posted earlier.

'{$PBASIC 2.5}
Sdat CON 15
baud CON 396

servoPos VAR Word

DO

servoPos = 500
' after the !SC, 14 is the servo channel (on the PSC), 3 is the ramp (speed), then the position
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 14, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 1000
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 14, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 500
' after the !SC, 15 is the servo channel (on the PSC), 3 is the ramp (speed), then the position
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

servoPos = 1000
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", 15, 3,  servoPos.LOWBYTE, servoPos.HIGHBYTE, CR]
PAUSE 2000

LOOP

And it worked! Then, after running it again three times, it stopped working. So um.. Yea. I really don't know. Is it possible I'm damaging something somehow?

Also, looking at the PDF manual on page 3, the plastic jumper thing on the diagram appears to be on the Vin side, rather than the Vdd side. Is that correct?

Unsoundcode · 2008-01-20 03:49

What you say raises a point, be sure the servo supply selector· on the BOE is set to VDD and not Vin,is that the jumper you refer too. Setting that jumper to Vin·could damage the PSC.

Jeff T.

Zoot · 2008-01-20 04:50

OK, back up. When you mean page 3 of the manual you mean the PSC manual, but it sounds like you are talking about the Vin/Vdd jumper on your BOARD OF EDUCATION? Is that right?

The jumper on your BoE must be set to Vdd if you are plugging the PSC into one of the servo ports on the BoE. The "power" that goes through the red wire from the servo port to the PSC needs to be the "regulated" Vdd -- which is a stable 5v. Vin is raw power from the batter and *could* damage your PSC.

- jumper on BoE to Vdd

- no jumper on PSC (so it responds to channels 0-15)

- plug a servo into any channel on the PSC and run the code I posted most recently. Wait at least 64 seconds and the servo should move through it's cycle twice.

- if not, triple-check your connections again and go through the PSC manual one step at a time. It can be tedious sometimes, but it's always worth it.

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
When the going gets weird, the weird turn pro. -- HST

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skatj · 2008-01-20 05:01

It was always set to Vdd so that's not the problem, the diagram in the manual looked different from mine so I was just asking to cover all bases. I ran your code before to no avail, I emailed Parallax and I'll just keep trying different things for now =/

skatj · 2008-01-20 21:00

Well, so here's what happened morning.

I took out my stamp and ran some code.

'{$PBASIC 2.5}
ch VAR Byte
pw VAR Word
ra VAR Byte
Sdat CON 12
baud CON 396
ra = 7
ch = 0
DO
pw = 1250
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
PAUSE 1000
pw = 250
SEROUT Sdat, Baud+$8000,[noparse][[/noparse]"!SC", ch, ra, pw.LOWBYTE, pw.HIGHBYTE, CR]
PAUSE 1000
LOOP

(Channels and stuff were correct). And it worked, again. After running it a couple of times, it stopped working, again.

I then tried your program that inputs position values through the DEBUG terminal, and that didn't work either. (I triple checked channels) In fact, the PSC wasn't even holding it in place. I could push the servo horn without any resistance at all. (the green LED still flickered though).

So I turned it off and went to work on another project, and disconnected it from the stamp.

And then...

I heard a gurgling sound and I looked around frantically for the source - It was my battery pack: one of the batteries leaked a blackish liquid! My PSC was off and disconnected at the time, so I don't know if that damaged it somehow, but this makes me suspect that the underlying cause of all my problems is with the power. Any ideas guys? What does this battery leak mean?

(All batteries were fresh from the same box, btw)

Post Edited (skatj) : 1/20/2008 9:05:06 PM GMT

Unsoundcode · 2008-01-20 21:12

The batteries are probably shorted somewhere, could be where you soldered them to the board or maybe you forgot to switch off the servo supply. In some ways this could be a good thing, it's pointing to the probable cause why your PSC is not working. Try removing your solder joints and connecting the battery leads to the screw connectors.Unplug the servos and with no batteries check with an ohmeter between servo positive and negative at the blue screw connecor.

Jeff T.

skatj · 2008-01-20 21:21

Unsoundcode said...
or maybe you forgot to switch off the servo supply

What do you mean by this? I've been meaning to ask this, but is there some protocol on what to turn off when you're DLing a program? I usually turn off the PSC first, then switch the Stamp power back to 1, DL the program, then turn on the PSC and switch the stamp power back to 2, but I know there are times when I didn't follow this order.

But yea, I'll try connecting the battery leads to the terminals this time.

(I heated up the solder on the pins and sort of flicked it off, if there's a little solder left on them but they aren't touching the other pins, that's okay right?)

Problem with Servo Control (PSC)

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