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Blog Smarter Life Challenge: Progress on The Robot Arm
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  • Author Author: PaulMakesThings
  • Date Created: 2 Dec 2013 2:19 AM Date Created
  • Views 690 views
  • Likes 3 likes
  • Comments 5 comments
  • psoc4
  • smarter_life_challenge
  • robot
  • smarter_life
  • auto_barista
  • arm
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Smarter Life Challenge: Progress on The Robot Arm

PaulMakesThings
PaulMakesThings
2 Dec 2013

I've gathered most of the components I need, including several 2A stepper drivers, a salvaged turn table base, and several stepper motors, mostly nema 17 and 23 bipolar. In my previous post I mentioned in a reply that DC servos sounded like a good option, that is still true, but I figure it's best to use what I have, and steppers and drivers for them abound at the Milwaukee Makerspace. I have used some of my contest funding to buy several encoders which I can integrate later to keep the steppers homed in. They could also be used with some gearmotors to make precision servos.

 

I will share the files when it is more complete. I have an overall plan for the arm, but started the drafting with the hand, as it is one of the most challenging components. I'm using 3D printing to quickly test and update the design. Currently I have the wrist tilt held level by a parallel bar linkage which can later be motorized to ad a 6th degree of freedom (DOF), the roll is controlled by a gear which fits around the wrist bearing. The motors rolling and gripping will be positioned at the back of the elbow as a sort of counterweight.

 

I've been playing with different ways of transmitting the motion, at first I had a pull cable in the hand with a spring to open it. I figured this would work fairly well since extra force on the open isn't needed and it would mean that by adding a swivel to the line I could rotate the wrist as much as I want with no tangle. I've also made a version that has a full loop so the motor could pull open and closed, this limits twist but gives more precise control.

 

The most up to date hand design is in the 3rd picture, that collar at the back holds the bearing and has a smaller bearing for the pinion which will drive the wrist, the plan is to run it through a universal joint which will run to the motor at the back of the elbow. Since I can print and try these things fairly quickly I haven't settled on that design, and I may switch either or both actions to use a push/pull rod.

image

Picture 1: CAD and real models. This is the 2nd revision of the hand, none of the other models show the rubber grippers, these are just case feet, but they allow it to pick up a coffee cup. Next to that, the CNC turntable I got for the base of it all, it's been abused a bit so I got it for a good price, but it has a little bit of backlash, still, it's the perfect size for this arm.

 

image

The gears inside the arm. This is a common design, so I can't take credit for the idea, just this implementation of it. The grips are made to fit the curvature of a coffee grinder bucket, since that is a bit larger than a coffee cup.

 

image

My current CAD model. The body of the arm is started but still too skeletonized to show off much. The wrist contains a bearing and a retainer.

 

Next up, stepper drive code and more of an arm

 

I'm using stepper motor drivers with built in controllers (DRV8825), so all I need to output is step and direction. The PSoC has an advantage here because the configurable digital can take much of the timing work off the CPU. I don't expect to have a system smart enough to actually find objects within 6 weeks from now, so I will be focused on controlling to taught positions. I plan to go as far as acceleration curves and coordinated moves, and I will build it with expanding to add streaming G-code in mind.

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  • cy.gul
    cy.gul over 11 years ago

    very cool 3d printed parts!

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  • PaulMakesThings
    PaulMakesThings over 11 years ago in reply to vsluiter

    Once I added the rubber case feet (seen on the prototype on the first picture) it could pick up a coffee cup without pulling the cable very hard. I only tested that manually. The case feet themselves did start to come off, but since it was an ABS print I applied some acetone and they fused with it pretty well.

     

    The actuation seems very low friction, just enough to keep it from rattling. That ring gear on the back also bolts to flanges on the top and bottom plate, and that's what supports them. They are spaced 0.020" wider that the height of the moving parts.

     

    All the parts are printed at 100% fill, 2 walls, ABS.

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  • vsluiter
    vsluiter over 11 years ago

    That looks really, really nice!

    How is it in term of friction, both to the coffee pot, and in actuation?

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  • yuritikhonov
    yuritikhonov over 11 years ago

    Cool arm Paul! I love robots and your project is great :)
    Yuri

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  • DAB
    DAB over 11 years ago

    Nice update.

     

    I know that there are a lot of different control arm designs to choose from, so you should be able to find a lot of easy control software as well.

     

    Looks like you are making good progress.

     

    DAB


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