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When can we buy openbuild robotic joint ?

Discussion in 'General Talk' started by Fourchette, Sep 29, 2016.

  1. Fourchette

    Fourchette Well-Known
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    Hello

    I'm a big fan of openbuild. Its components are great for most linear applications.

    but now i want to go further and build my own serious robotic arm.

    I'm struggling to find open robotic mecanic joint and have little metal machining available (as in aluminium or steel) to build my own. It's also the reason why i love openbuild.

    The best alternative I have found until now looks like below (from igus)
    (please ignore the stepper motor in the image as i intend to use my own motoring solution)

    Do we have a chance to see appearing on openbuildspartstore.com any time soon ?
    How can i help to see that happening ?


    cheers
    fourchette

    source: igus® Blog INT | RL-D 4 DOF standard arm "big"
    [​IMG]

    [​IMG]
     
    MaryD likes this.
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    I wouldn't expect to see worm drive systems like those you have shown any time soon. Cost to manufacture would put them well beyond the hobbyist budget and make a manufacturing investment hard to recover. Direct drive is a little more feasible and there is already a lot that can be done with existing openbuilds parts. The only thing that is really missing is a proper hub. Had the jog knob been made with a 1/4" through hole it would be an easy drop in but it is also easily modified with hand tools to where it could be used as a hub for both 5mm and 1/4" shafts. Merely epoxy in an 8mm aluminum spacer, re-drill and tap the set screws and ream the center hole as needed.
     
    MaryD likes this.
  3. Fourchette

    Fourchette Well-Known
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    I beleive some of us are neither pro/industrial customers, nor hobbyists. Typically SMBs looking for cheaper and simpler, albeit being less precise or less durable options. My usecase here.

    Actually i am not a big fan of worm drive but mostly because i have yet to try it. And i have yet to find a direct drive option as well because most motors seemed too big + i have not found a cheap and easy planetary gears option nice and compact. Therefore i was thinking of a belt drive. It just seems easier and cheaper. But maybe this is just my ignorance when it comes to mechanics.

    Now for the joint itself, which is my core interest. Am i affraid i have difficulties understanding your description above. I lack vocabulary and expertise. Would you please point me towards and existing build using such techniques ? any book that i should read ? or maybe post picture ? what do you suggest i do next instead of just buying igus parts and hope for the best ?
     
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    As far as books go, I've never looked at any. I find instructables.com a decent source of information for level that I would be working at. (i.e. hobbyist.) I'm sure there is better information out there but I've had no reason to look for it.

    Nomenclature: A hub (or more specifically wheel hub) is just a means of attaching a plate to a motor shaft. Looking at a system like this you can see where the jog knob would fit as an interface between the two.

    The purpose behind worm drives is that they overcome a major issue with stepper motors. When the power is cut to a stepper motor it loses holding power and gravity takes over. So a direct drive arm (or a belted drive arm for that matter) would drop to the table when power ceases. Worm drives use gearing to achieve motion and are far less susceptible to release when power ceases. Granted, how resistant they are is all dependent on the ratio and angle of the gearing, friction in the system, inertia, etc. but you can easily see the benefit over plain steppers. This is why you see servos being used in many arms rather than stepper motors. Servos tend to stay put where you turn them off. A few examples of small arm systems can be found here.
     
  5. Fourchette

    Fourchette Well-Known
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    i see your point with worm drive but with my usecase, losing power or losing steps is not really a concern too. most of the time, the operation to perform happens in less than a minute and i usually have a homing cycle between operations.

    thanks for pointing towards the jog knob
    while facing heavy torque abrupt changes (such as spinning in one direction with a significant weight (say 2 kg), then immediatetly spinning in the order direction), aren't you affraid the two mini screws below would "slip" the shaft after a while ?
    [​IMG]
    Or maybe that manual operation you were refering too was about drilling the shaft itself for such tiny screw to actuall enter the shaft ?


    shouldn't i just use a "keyway" instead ? such as

    [​IMG] ref SC0810CKP4
    (not sure where i can find the "keyway" nor a compatible shaft, but that's another story)

    besides, all such options assumes there is a shaft.

    But since i am thinking of a belt drive system, the best joint would be two circular rotary panels/units, one of them having teeth to form a gear. such as "slewing rings" ?

    [​IMG](it does not need to be steel, i just google-image the keyword to illustrate my point)

    or is it too expensive or complicated ?

    i have no idea :|
     
  6. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    If you're talking 2 kg loads, yes it would need a keyway or at least a D-shaped shaft opening. But at 2 kg you're also getting beyond the hobbyist grade level of the parts here.
     

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