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Thread: HELP - Darwin Mini

  1. HELP - Darwin Mini

    Hi all

    I am fairly new to robotics (built a HEXY before)and just completed my Darwin Mini - great project. The robot seems to be working properly, but I notice two things:

    1. The front LED on the OPEN controller is lit up red. I cannot find a manual anywhere as to what that means (no rev c manual online, only rev a and b) - I notice on the youtube demos that the LED is not lit, so I guess something is wrong..

    2. When the robot is connected I notice a "gear grinding sound". I guess this is coming from one or more servos - any advice on resolving? Is this normal?

    Phil

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    Re: HELP - Darwin Mini

    Not sure about the LED, but the bluetooth module and OpenCM usually each have one or more LEDs turned on to let the user know that power is connected and that it will be trying to run the sketch and/or connecting to another BT device.

    Does it make the noise only during a part of the motion or is it continuous? Does it make the noise if you power off the bot and move the joints by hand? Is it a clicking or chattering, or just a pulsating groan?
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  3. Re: HELP - Darwin Mini

    Quote Originally Posted by tician View Post
    Not sure about the LED, but the bluetooth module and OpenCM usually each have one or more LEDs turned on to let the user know that power is connected and that it will be trying to run the sketch and/or connecting to another BT device.

    Thanks - there is a blue light at the back that I assume is the Bluetooth connection. The green one (right side) at the front comes on during power on, but then goes off - the red one (on the left) stays on. May not be a problem, just want to know why.

    Does it make the noise only during a part of the motion or is it continuous? Does it make the noise if you power off the bot and move the joints by hand? Is it a clicking or chattering, or just a pulsating groan?
    The noise is continuous and is a low level pulsating groan. I can tell that the noise is coming from some of the servos (not all of them), just not sure why. The robot performs fantastically, but this doesn't seem right (again, perhaps it is normal).

    Really appreciate the advice.

    Phil

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    Re: HELP - Darwin Mini

    The OpenCM has two LEDs: red is Power and will be ON whenever the board is powered; green is the user LED that can be used however desired within the sketch.

    Some amount of noise from the servo is expected from various influence of servo loading, the gearset, the motor, the control algorithm, and the electronics switching at frequencies in, or near, the average range of human hearing. There are a couple very annoying AX-18F that made a rather distinct high-frequency whine under certain horn loading conditions, and a sporadic 'tv static' or 'morse code'-like collection of noises/tones under others, because of how the control algorithm was switching the H-bridge (there is a PC power supply in the lab that makes a similar whine). If you put the bot in one pose then pick it up (or just move the limb a little bit within the backlash of the gearset) so that the servos are not supporting the weight of the bot, does the sound change or go away?

    There are a few sounds and behaviors that are never nice to hear or feel from a servo. A damaged gear is the likely culprit if there is a loud clicking sound, or if the servo is unable to reach/maintain a certain position while powered off (not due to frame interference), or if there is a periodic sticking/skipping when rotated while powered off. Damaged brushes in the motor can result in an increased resistance to rotation while powered off and quite a bit of extra noise when powered. Having the output shaft of the servo shear off will usually cause an inability to maintain a horn position for a significant range of the servo (the screw securing the horn may lock the horn to the output gear for some direction/part of the rotational range).
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    bleh

  5. Re: HELP - Darwin Mini

    Thanks so much - I assume everything is normal then! Funny how they used red for power :-)

    Quote Originally Posted by tician View Post
    The OpenCM has two LEDs: red is Power and will be ON whenever the board is powered; green is the user LED that can be used however desired within the sketch.

    Some amount of noise from the servo is expected from various influence of servo loading, the gearset, the motor, the control algorithm, and the electronics switching at frequencies in, or near, the average range of human hearing. There are a couple very annoying AX-18F that made a rather distinct high-frequency whine under certain horn loading conditions, and a sporadic 'tv static' or 'morse code'-like collection of noises/tones under others, because of how the control algorithm was switching the H-bridge (there is a PC power supply in the lab that makes a similar whine). If you put the bot in one pose then pick it up (or just move the limb a little bit within the backlash of the gearset) so that the servos are not supporting the weight of the bot, does the sound change or go away?

    There are a few sounds and behaviors that are never nice to hear or feel from a servo. A damaged gear is the likely culprit if there is a loud clicking sound, or if the servo is unable to reach/maintain a certain position while powered off (not due to frame interference), or if there is a periodic sticking/skipping when rotated while powered off. Damaged brushes in the motor can result in an increased resistance to rotation while powered off and quite a bit of extra noise when powered. Having the output shaft of the servo shear off will usually cause an inability to maintain a horn position for a significant range of the servo (the screw securing the horn may lock the horn to the output gear for some direction/part of the rotational range).

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