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Designing T-Bot

Discussion in 'DrawBot' started by Rakesh Raghvani, Sep 18, 2018.

  1. Rakesh Raghvani

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    Hello,

    Is it possible to use one gantry plate in-between two v-slot linear rails (20x60mm) so that it can be moved along the X and Y axis?

    I want to build a T-Bot similar to this design H-Bot…Just for fun at Buildlog.Net Blog, but I don’t know what gantry size I require, and I’m not sure whether it’s possible to have wheels on both sides of the gantry using the same holes.


    Thanks
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Absolutely. Here is an example for C-beams but a similar approach is viable for the belted example you referenced.



    You can download this example XY plate file here C-Beam XY Example Plate.zip
     
  3. Rakesh Raghvani

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    Thanks Rick 2.0, that’s exactly what I want. However, I don’t have a CNC machine to make my own part – yet!

    From openbuildspartstore.com, what gantry would I require, to achieve similar results? Is there anything else I need to consider, such as bolt sizes etc?

    Apologies in advance with the questions. I’m new to v-slots.
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Unfortunately there is no single plate that will do the trick. You might be able to make it work with a couple of V-Slot Gantry Set - Universal mounted back to back which would actually be similar to the referenced example. You will need 4 extra wheel kits, 4 extra M5x25 screws and 4 additional 6mm stand offs. You will also need to drill (4) 5mm holes in the plates for the additional wheels.

    Personally, I would take a scrap of 4mm aluminum and make/drill the plate myself. Hand made plates are really not that difficult.
     
  5. Rakesh Raghvani

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    I think taking a sheet of aluminium and drilling a few holes would be the easier option.

    Thanks again.
     
  6. Rakesh Raghvani

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    Here's my plate. Wasn't that hard to make after all!

    IMG_20181015_203850.jpg IMG_20181015_203819.jpg
     
    Amirali Nafe, MaryD, crispin and 2 others like this.
  7. Rakesh Raghvani

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    After purchasing the various V-Slot parts and building a suitable gantry plate, I’ve now managed to build my T-Bot. The T-Bot will eventually be used as a drawing machine, similar to AxiDraw, but using SlushEngine Model X LT and Raspberry Pi 3. Here’s my first working version on YouTube. My next task is to read G-Code and make to T-Bot move according to the coordinates.
     
    MaryD likes this.
  8. Rakesh Raghvani

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    I’ve made a T-Bot similar to this design. Using stepper motor driver L6470, I can control the movements e.g. up/down, left/right and diagonally using the equations shown here corexy, via the L6470 command MOVE(direction, number_of_steps) using MAX_SPEED(100 step/s).

    If I move from (0, 0) to (400, 400), both stepper motors move at a constant speed, and reaches (400, 400). Great.

    If I move from (0, 0) to (400, 100), then I need to reduce the speed of one of the stepper motors by 4 times (400 / 100 = 25 step/s). Fine.

    However, if I move from (0, 0) to (400, 300), I reduce the speed of one of the stepper motors by 1.3 times (400 / 300 = 1.333 step/s). Slight issue here, MAX_SPEED only accepts integers and therefore the linear path it follows is not correct – one stepper motor will stop before the other, and a diagonal line is not drawn correctly.

    Is there a way of resolving this issue?
     
  9. Rakesh Raghvani

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    Update,

    As I was unable to use the methods provided by the L6470 chip, to do what I wanted. I have now used Step Clock mode instead. I have written methods which allows me to rotate the stepper motors a step (i.e. 1.8 degrees); using Bresenham’s line algorithm to draw diagonal lines without having to decrease or increase speeds.

    Here’s a little video, which follows some basic coordinates.
     

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