$50 Robot Servos operate sparatically

[maxonr]

hi,

I build the $50 Robot with my son.  It all came together after a lot of work.  We Ohm'd and passed the smoke test, then checked voltages, so we think our solder work is good.  However when we plug the servos in they operate sparatically, even though we have a constant 4.8v at the connections.  I hooked the servo directly toa 9v battery and we get the same sparatic operation.  I opened the servo up and put current directly to the servo motor and it run continously.  There must be something in the circuit board of the servo.  (BTW both servos operate this way)

has any one got any ideas or thoughts?

thanks,
rich

[VegaObscura]

If you're using the photovore code, then the problem could be your light sensors. 

Download this fine and upload it to your bot:
http://www.societyofrobots.com/downloads/hold_servo.hex

Then once your bot is on, your servos shouldn't move at all.  Try to move them with your hands.  It should be hard to turn.  Turn your bot off and try to turn the servos again.  Was it harder to turn the servos when the bot was on?  If so, your servos are working correctly and your light sensors or your code are likely the problem.  If the servos move constantly when the bot is turned on, don't resist being turned, or still move erratically, the problem is in your servos or your board.

[Conscripted]

I'm going to agree with what VegaObscura said. I had a lot of trouble with my light sensors. I never got them to work quite right. Eventually I replaced them with a sharp IR sensor and never looked back.

Conscripted

[maxonr]

Thanks.  I tried your code, and it doesn't hold the servo motors. 

However, shouldn't the servo motor run(or pulse) continously when hooked directly to a battery?  They do not, they run sporatically. 

thanks,

[Conscripted]

However, shouldn't the servo motor run(or pulse) continuously when hooked directly to a battery?  They do not, they run sporadically. 

Are you talking about opening the case and applying power to the motor or are you talking about connecting the red and black wires to a battery?

A servo is basically a gear motor with a lot of control circuitry built in. The control circuitry looks for pulses on the signal wire to move the servo to some position or another (based on pulse width). When you connect the servo to power (red and black wire) the servo will probably twitch. That is normal.

Did you have any trouble modifying your servos for continuous rotation when you built your bot? What servos did you use? Did they work when you loaded the hex file to center them?

What exactly happened when you loaded up that hex file that VegaObscura provided? Will you please describe the servos behaviour. "Sporadically" doesn't describe what they are doing exactly.

Conscripted

[maxonr]

I putting power to the red/black wires coming out of the servo.  WHen I say 'sporatically', what it really does it twitch randomlly.  at unspecifided intervals the servo motors start/stop rotating.    I didn't seem to have any issues when I modified them.  I am using HS-311's  I didn't have a microcontroller to center them, I did what I thought was good by hand. 

When I uploaded the that hex file that VegaObscura provided, it didn't seem to work at first. I unplugged the battery and one servo exhibited the behavior described.  It held, and I couldn't turn it with my hand.  I could feel that the motor was holding the wheel. 

does the battery need to be unplugged when removing the programming dongle?  I will try to upload the hold hex file again, and the photovore.

thanks so much,
rich

[VegaObscura]

I putting power to the red/black wires coming out of the servo.  

This would not make the servos turn.  This will power up the servos, but they don't turn until they're given a "signal" on the yellow or white wire.

I am using HS-311's  I didn't have a microcontroller to center them, I did what I thought was good by hand.

This definitely sounds like your problem right here.  Without a microcontroller to center the servos, you have no idea whether your pot was centered or not.  Now that you have a microcontroller, open up your servos and do the modification process again.

I unplugged the battery and one servo exhibited the behavior described.

Wait... the servo was holding without being plugged into a battery?  Or do you mean it was holding when the battery was connected and then released when it was removed?

does the battery need to be unplugged when removing the programming dongle?

Yes.  This is from step4 of the $50 bot tutorial:

Plug in your AVR STK Serial Port Dongle Programmer to both your computer and your robot if it isn't already from Step 3C. AFTER plugging your robot in, turn on the microcontroller by flipping the ON/OFF switch, or plugging in the battery if it doesn't have one. If you were to unplug the programmer, make sure you turn off your robot first.

Finally, try uploading the .hex file attached to this post.  What its supposed to do is go straight, turn left, go straight, turn right, and repeat.