Virk I

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Virk I, my current project, is a 3 DOF mini scara desktop robot targeted to education and hobbyists. It’s a quality, robust, neat and cute robot, designed, machined and assembled in my workshop. If everything goes well the design will be released as open hardware in the near future.

Main features are:

  • Three bearing, hollow axis precision rotary joints
  • Linear bearing on Z axis
  • Wooden, slim structure
  • Compact and easy to carry

Price for a complete, functional unit, will be around US 2k (free international shipping included) .  If you wish more information, just send me an email to igarrido@automaticartisan.com.

 

Current status and plan

Currently there is a lot eight units being built. What is left:

  • Gripper construction (design was finished on Oct. 4th)
  • Homming switches
  • Software testing
  • Asthetical improvements

I’ve discarded to sell the arm without the gripper, so I will put units on sale only once they will be completed, hopefully at the end of this month (October).

 

You can see Virk I first moves here.

 

Specs

  • Australian blackwood body
  • Motors: Nema 17  stepper on rotay joints, Nema 11 stepper on z axis
  • Full extended range: 26cm (from shoulder axis to end center)
  • Travel: ??° on base, ??° on elbow,  75mm on Z.
  • Weight: ?? kg without electronics.
  • Rotary joint: three bearing, acetal/pvc construction, hollow axis, modular.
  • Z axis slide: 8mm linear rails.
  • HTD3m timing  belt on rotary joints.
  • 8mm pitch leadscrew on Z.
  • Homing switches.

 

Hollow Axis Rotary Joint

One of the most interesting part of this robotics is our custom designed, hollow axis modular rotary joint. Being hollow axis means that the wires can go hidden and not be a mess as in other designs. And is modular as you can reuse this joint in your own robotic designs; you only need two flat surfaces and some holes.

This joint has three bearings inside: two trust bearings and one deep groove, thin bearing. It has three acetal parts and one PVC mount base. Also, there’s a custom made timing pulley attached to the rotating part of the joint.

There’s currently no spare joints to be sold, but if there’s enough interest maybe I make some of them to be sold.

 

Electronics and software

First set of prototypes will use RAMPS 1.4, the standard for many 3D printers today.

As for control software my aim is that, at some point, someone from the open source community creates or adapt a suitable software for this kind of arm. As far as I know you can download grbl source, make some  changes, and get a basic but usable software interface to start with. In fact, first tests are currently being done using grbl as is, so I can move the arm, though I don’t have real position control.

 

Q&A

  • ¿Could be used to engrave? I don’t think so. This arm has enough power to move itself and lift small things, but lower enough so it can’t damage itself or the user. Engraving requires more stiffness and power.
  • ¿Could be adapted for 3D printing? Maybe, but I guess this will not be practical. Belt transmission and arm mass add some “spring effect” on every movement, so the faster, the less precise. That is, of course, just theory.
  • ¿And the gripper? The gripper will be tackled once the eight units be ready. I’m currently working on the gripper.
  • Your arm lacks a theta axis on the end of the Z, hence isn’t a full scara robot. Technically right. I’ve I have left aside the theta axis for the sake of simplicity, but in the future I wish to be able to provide this as an option.
  • ¿How much precision can you get from this? To be honest, I don’t know. Rotary joints are very precise, but final precision depends on a lot of factors: calibration, proper belt tension, load, belt fit, total stiffness, etc. I guess it will be precise enough to be a useful as learning tool and to give fun to robot lovers.
  • ¿Why wood? Because it’s beautiful, cheap, lightweight and easy to work. And because I love wood.
  • ¿What kind of machines and skills I need to make something like this? You can probably do all the parts using a cnc mill or a good cnc router. A manual or cnc lathe will be handy, too. This is not a simple project, and has a lot of parts, so you need to have experience using cnc  machine and be able to grind your own cutting tools. Also. you will need a lot of tools; drills, taps, etc.
  • ¿Could this be 3D printed? May be on a professional 3D printer, not in a reprap style one. Typical 3D prints lack required precision and strength. I guess some wood parts could be 3D printed, but not the rotary joints and other precision parts.
  • When will be the design available as open source? Currently, I have just some messy draft drawings for just some parts, so a fair amount of work will be needed to get a decent set of understandable drawings. I will start working on the drawings after the eight units be finished and sold, and probably will publish first the rotary joint design, very likely before the end of the year. The full design will be published when I finish the second lot of units, hopefully within Q1 of 2019. However, if I’m not able to sell all the units on the first lot I will understand it’s not worth the effort to publish the design.
  • This will be a ready to use product? No actually because of the lack of software, but I hope it can be on the future. I hope some talented people of the open source community be interest on make some developments for this kind of machine. Anyway, complete units will be shipped with grbl so end owners will be able to test robots movement and play a bit.
  • Why so few units? Because this is actually a one-man project and I don’t intend to turn this into something bigger. My hope is to be able to produce small lots of this arm one or two times a year.
  • Can I take your design, built it and sell it once Open Sourced? Yes. The more people have access to this, the better.
  • You say your units will be prototypes. Will they have issues? I’ve worked hard to make things right, but I will provide required support if something goes wrong. Just don’t buy this if you want something bulletproof or don’t wish, eventually, to fix things by yourself with my help.

 

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