Change motion from rotation to linear

Home Forum Stewart/Gough Platforms Change motion from rotation to linear

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  • #27926
    AvatarKevin
    Participant

    I got a good start, I think. Some of the confusion was understanding the terminology. These pictures are what I think I discerned from my observations and assumptions.

    https://photos.app.goo.gl/F1sPXpLVqYmuEmPQA

    I think I sorted out some of the configuration:
    // measurements based on computer model of robot (in cm)
    #define NUM_TOOLS (6)
    #define BICEP_LENGTH ( 5.000)
    #define FOREARM_LENGTH (50.0)

    // top center to wrist hole (relative): X7.635 Y+/-0.553 Z0.87
    #define T2W_X ( 15.5)
    #define T2W_Y ( 4.5)
    #define T2W_Z (-1.0)
    // base center to shoulder hole (relative): X8.093 Y+/-2.15 Z7.831
    #define B2S_X ( 10.5)
    #define B2S_Y ( 14.0)
    #define B2S_Z ( 1.0)

    The next thing I need to sort out is how to change the motion from rotation to to linear.

    From looking at the code, it seems like I need to get rid of the bicep. Looks like in update_ik I need to get rid of update_shoulder_angles. Should be that a lot of the code should get a lot simpler, right?

    Anyway, I am done for the day. Thanks!

    #28961
    Avatarcrazymike
    Participant

    Hello Kevin,
    I’d like to build a linear hexapod as well. Did you get any further? As seen on youtube Dan already built a linear actuated hexapod (https://youtu.be/btxdl1TQBTw) but I don’t think the code is available in the git.
    My understanding of Dans code is the same, I guess we could change it and it would get ‘shorter’ .. I will try to figure out how … (Don’t know if I am capable of doing it due to my limited programming knowledge)

    #28963
    DanDan
    Keymaster

    The number one thing that stopped me from making more stewart platforms like this is that the linear actuators don’t have linear position sensors. Without that I don’t feel I can safely move the system around. Yes, there are less good ways of doing things – like limit switches and dead reckoning. I’m want reliable results.

    #28964
    Avatarcrazymike
    Participant

    The Actuonix actuators which are used quite often (little bit pricey) have a potentiometer ( Feedback Potentiometer: 2.75 kOhm/mm ± 30%, 1% linearity)
    Do you think this will be sufficient ?
    My plan is to use t5 lead screw actuators nema 11 homebrew design.

    There is an other code source which looks very interesting for building these type of robots
    https://github.com/shoarai/ParallelMechanism/tree/master/src

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