Making Thor Fail

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  • #2184
    RobotArmature
    Participant

      Hi,

      I’m a university student in NZ doing a thesis on a new type of 3D-printed polymer and my partner and we are looking at the Thor arm as a test subject. To do this we’ll be focusing on material testing and were wondering how and where the thor bot typically fails mechanically.
      A large portion of the robot’s bulk appears to be in the first and second arm sections, with a much smaller third arm. Which of these arms fails firsts and are they all fairly equal in strength?

      Zac.

      • This topic was modified 8 months, 3 weeks ago by Angel LM. Reason: Moved to Get Help > Others category
      #2186
      Angel LM
      Admin

        Hi Zac!

        First of all, thanks for your interest in this project! I am very happy that after years, this robot is still being studied 🙂

        To answer your question, indeed, in terms of load support, joint 2 is the one that has to support the most, followed by joint 3.

        In terms of mechanical failures, the most sensitive parts and the ones that have ever broken are the gears that attach directly to the motor shaft. They are sensitive for two reasons, the first being temperature: Motors get hot during robot operation, and as the printed parts are in direct contact with the motor, they can reach temperatures high enough that they become malleable and deform due to the combination of stress and heat. That is why for all small parts that are in direct contact with the motors it is recommended to print them in ABS.
        The second reason is the force that the gear teeth have to withstand. As they are small parts and are printed, due to the force they are supporting, if the layers are not well bonded to each other, they can break.

        In the rest of the structure of the robot I have not observed mechanical failures of this type, but there is another that occurs in many axes and has to do with the flexibility of the assembly of the parts and their clearance. For example, the body of joint 2 (the one formed by the 8-shaped pieces and their intermediate connection) can be seen as an H if you look at it from the side. Because the connection of this body is only in the middle, when it is subjected to a lot of load the ends (especially the lower ones) tend to open up a bit. If this opening is large enough, the gears of the motors may not make good contact with the inside crown of the second joint, which can cause anything from a loss of steps of the motors to gear breakage.

        Regarding the mechanics, these are the faults that I have detected the most, I hope it is of help!

        #2188
        RobotArmature
        Participant

          I’m not sure if you can view the message that was deleted but I’ll try and summarise it.

          The material that we’re looking at using is based on PLA and is a mix to create a less brittle 3D printable biodegradable polymer, and so, this material will be primarily focused on replacing the PLA sections. We might test this for the gears but it seems unlikely to be suitable from what you’ve said. To this end, we might substitute the gears for another material that might be better suited than ABS.

          For the weight limit of the arm, is this due to the torque of the motors or the failure of the gears?

          #2189
          Angel LM
          Admin

            I am sorry that the previous reply has been deleted, the anti-spam system has deleted the message and I am not able to recover it.

            Regarding your question, currently with ABS printed gears, the limit of the robot load is due to the maximum torque provided by the motors.

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