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Thread: Hexapod in vertical surfaces

  1. #11
    hoanglanjvb Guest

    Re: Hexapod in vertical surfaces

    Wonder if you might be able to do some query of the servo for error conditions? If you are using individual writes to the servos, than the status packet (assuming you have not disabled them),

  2. #12

    Re: Hexapod in vertical surfaces

    Again I am guessing that there is a thermal shutdown of the servo.

    As Kevin mentioned, when you are in a vertical position the Coxa servos are having to support all of the weight.

    My (ex)Math skills are really rusty, but have you calculated how much torque you are needing these servos to support?

    Things like center of gravity or ... I would probably start off doing some simple calculations, like weigh the whole robot and then maybe divide that by 6 (all legs on the ground) and maybe 5 (one leg off the ground). Then I believe there is a simple calculation to take this and also use the calculated leg length (how far is the tip of the foot away from the servo) and calculate the torque.

    Then look at the specifications of the servos, example AX-12 says it has a stall Torque(Nm) 1.5 at 12v... (And a stall Current of 1.5 amps).
    How close are you to these maximums?

    I believe that it is recommended that you do not typically exceed 1/5 of the stall torque. Hopefully there are others up here who know more about these limits.

    Also depending on your setup, I don't know if maybe adding something to relieve the stress on these servos like Springs would help? Again others may be able to help if they saw more of your design. But maybe assuming standard(ish) hexapod, adding springs that are above the servos (when going in the up position), might relieve some of the pressure. May have to be careful on how much spring, as what happens when the foot leaves the ground?

    Again it would help verify the thermal issues if you had the code try to read the servo current temp during the loops and maybe see what they are doing.

    A I mentioned, highly probable that you are overheating the servos and they are going into thermal shutoff. But could also be power issues.

    That is if all of the servos are running at maximum stall torque, maybe your power source is being strained, the voltage drops, and one or more processors reboot...
    Last edited by KurtEck; 04-23-2018 at 10:18 AM.

  3. Re: Hexapod in vertical surfaces

    Ok, thanks for your answer, I will check your advices. The thin is why the leg fall down before up, the five legs that are in contact with the surface support the weight, and the leg that is going to move is able to move up an down.

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