Boe Bot (USB) Servos Unresponsive

manaox2

It seems my Servos have stopped responding. I wrote a test program that worked previously.

' {$Stamp BS2} ' Stamp Directive
' {$PBASIC 2.5}
pulse_count VAR Word ' Declare a VAR. FOR counting
 
DEBUG "Clockwise 3 seconds "
FOR pulse_count = 1 TO 122 ' Sends 122 clockwise right pulses
PULSOUT 12, 650 ' 1.0 ms pulse TO right servo
PAUSE 20 ' PAUSE FOR 20 ms
NEXT
DEBUG "Stop 1 second "
FOR pulse_count = 1 TO 40 ' Stop in 40 pulses
PULSOUT 12, 750 ' 1.2 ms pulse TO right servo
PAUSE 20 ' PAUSE FOR 20 ms
NEXT
DEBUG "Counterclockwise 3 seconds "
FOR pulse_count = 1 TO 122 ' Sends 122 right pulses
PULSOUT 12, 850 ' 1.0 ms pulse TO right servo
PAUSE 20 ' PAUSE FOR 20 ms
NEXT
PAUSE 500 ' PAUSE FOR 0.5 s
END ' END

I have made sure its position is on 2 on the BOE board and tested different batteries. I have even gone as far to try setting different power sources and a replacement BS2 stamp. When I set the jumper for the power source, then the·Stamp Editor no longer recognizes the stamp (?) Can someone provide some suggestions?

I have the red wire attached to P2 and the black wire attached to Vss.

Robert1770

Are you seeing all of the debug information on the editor?

Have you tried connecting the 470 Ohm resistor and LED to pin 12 as shown in the student guide page 48? Is the LED lit?

Have you tried using another servo on pin 12?

Have you tried the pulsout on pin 13?

You might have a broken connection.

I might have some more ideas once I get my Boe-Bot and start playing with it.

Robert

manaox2

I have tried everything but the LED, which btw, is a great suggestion. The debug information shows up, but neither servo works on either pin 12 or 13. As soon as I can try connecting the resistor and the LED, I'll get back to you.

manaox2

LEDs work fine... ·They visibly dim though when I unhook and connect the servo back that it is controlling though. I hope that gives you a hint.

Post Edited (manaox2) : 3/28/2007 5:24:57 PM GMT

Chris Savage

If you ever used a power source with too much voltage, such as a wall adapter you may have damaged the servos.

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Chris Savage
Parallax Tech Support

manaox2

what is the proper voltage for the·servos? I know it uses pulse, but it seems to be four volts coming out to them from the robot. (I'm using a multimeter to diagnose any problem)

EDIT: considering that the servos might me damaged, I connected them to a 9V battery directly. It works when you tap the connectors to make a pulse... its one directional as well. This makes me think that they should still work.

Post Edited (manaox2) : 3/28/2007 6:10:26 PM GMT

Chris Savage

Hello,

I think you may have misunderstood what I was saying…The servos must have a separate power source…The signal that drives them is not the source of that power. It sounds like you’re measuring the voltage at the signal pin to get this 4V. As a note, 9V is technically too much…If you did it for short periods of time it would be okay, but running the servos from 9V continuously would be very bad for the life of the servo. The typical range is 4.8V to 6V. Take care.

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Chris Savage
Parallax Tech Support

manaox2

I believe I am confused. What do you mean by a second power source? I am being encouraged to learn a lot very fast for a class of mine.

Mike Green

Servos have 3 wires coming from them. Usually one is red, one black, and one white. The red wire connects to the positive terminal of a power source of between 4.8 and 7.2 volts capable of supplying perhaps 1 amp, perhaps more under peak mechanical loads. This power source supplies power to the motor and the servo's electronics. The white wire connects to the control signal which supplies a series of 5 volt pulses between roughly 1 millisecond and 2 milliseconds in duration, repeated about every 20 milliseconds. This control signal (by its width) indicates the position the servo should move to. The black wire is the ground lead and should be connected to the negative terminal of the power source AND the ground connection of the controller that supplies the control signal. This controller often has its own power supply to prevent problems with electrical noise from the servo motors. Commonly, when the servos are operated from batteries, the controller through a regulator may also run off the same battery. The regulator helps isolate the controller from the noise and voltage drops caused by the motor(s).

Does this help your confusion?

manaox2

Yes.. that clears things up on that. Its too bad that it only makes diagnosing my problem harder it seems. I may have to give up and move to a different platform soon (and right after getting the serial print kit too!)

Chris Savage

manaox2 said...
I have the red wire attached to P2 and the black wire attached to Vss.

Are you still connecting like this?· How are you doing this?· You should have the servos connected to the X4 and X5 connectors with the white wire toward the outside of the board.· In this manner the red wire will not be attached to P2.· If putting the voltage jumper on causes the Stamp to not be recognized, that is a symptom of a short.

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Chris Savage
Parallax Tech Support

manaox2

Those wires are refering to the piezo crystal speaker that I was using to test before. They are connected to the board with a red and black wire unrelated to the servos. I just named the color to help distinguish the negative and postive connections. I have my servos connected to X4.