Finally

It’s been a while. The first unit of Virk I has been finally finished (more than a month ago, indeed). There’s a fourth working axis now and I’ve polished my modified Marlin version.  Currently, I’m working on a simple python program to implement some simple tasks using OpenCV. Here’s the video.

The python software runs on a computer with a webcam, and the perspective transform is used to convert camera coordinates to robot coordinates. This implies a previous calibration process using four points. Eventually all this stuff could be, as far as I know, run on a RPI, thus avoding a full computer on the chain.

I’ve been decided to postpone the Open Hardware thing, as there’s really no interest, probably because the trend today is to 3D print arms, and milling is too overkill for most people.

So what’s next? I’m not sure. Maybe I’ll finish the other units and just try to sell them. Or I could make something else with all those robots. To be honest I will love to open a place with robots and cnc machines, where people can interact with robots and see cnc machines in action. A place to learn and have fun. Or maybe I will start to make and sell just some simple crafts. Who knows.

Currently, I’m competing on several local entrepreneurship contests, searching for a business plan, talking with people to get feedback, etc. In a few words, I’m going outside the shop, into the real world. Any ideas about my new direction now?

 

 

 

Virk I – Open Hardware Scara robot

This is a Virk I, a project I’ve been working for a long time. It’s A small, slim 3-axis scara wooden desktop robotic arm. It was meant to be a learning tool or hi-tech toy. The design will be open sourced once the first phase be accomplished and all the units on the first lot be sold. The aim is to provide a small, portable, quality and beautiful robotic arm alternative, either for the academic or applied hobbyist.

Current version it’s made of Australian Blackwood (Acacia melanoxylon), acetal, pvc and standard components. Most parts where machined on a cnc mill/router/lathe.

On the shoulder and elbow it has custom design, modular hollow axis rotary joint containing three bearings inside. Two thrust bearings give the joint very low play, allowing soft, low play movements. Being hollow means that you can route the wires inside the robot most of the time, so you don’t end with a mess of wires outside, and get a more cleaner look. On the z axis it has standard 8mm linear bearing rails.

Rotary joints are driven by a nema 17 stepper coupled to custom made 3mm pulleys. Z axis is driven by a nema 11 stepper linked to a 8mm pitch leadscrew. There’s currently no gripper on the end of the arm; gripper design and built will be tackled once the first lot of eight robots be finished.

Currently, it’s driven by RAMPS 1.4 electronics. As far as I know there’s no open source 3D printer firmware able to drive a scara robot, and it’s outside the scope of this project to make such a development, so final owners will have a challenge making this thing work. Of course you can use something like grbl to test the robot movements, but to be useful you need a firmware containing scara kinematic support. Maybe this marlin based parallel scara source could be a starting point.

I’m currently starting to test the first working unit and solving some final design issues, so the very first units to be sold will be available, very likely, at then end of this month (September).

You can find more info here.

Video here.

Update: It has been pointed out here and at hackaday that there are several platforms already supporting scara  kinematics:

  • Smoothieware: Morgan-scara: not single arm scara, but close.
  • Machinekit: According to the documentation, it has scara (single arm scara) support.
  • Reprap-helios:  That seems to be a similar arm, so I guess the same firmware could drive Virk I (I haven’t checked current status of this project).
  • Marlin for single arm scara: This seems to be a suitable option. I will test this at some point.

I would love to hear about someone experiences using those platforms to drive a scara robot.

Wood clamping

I’ve been making a lot of wood parts lately. Here, I show the three main ways I use to clamp the wood.

Long stick on vise

This is easy.

Pros: Low setup time, great for series.

Cons: Final cut-off should be carefully planned.

Disposable wood support

This is my favorite. You  just glue a piece of “decently” squared wood to the base of your blank, and use it to clamp to the vise. After machining the top and the sides, you cut away the base block and machine the underneath.

Pros: “Indexable”: you can use a vise stop so you can put your part on exactly the same position several times. So, if you have a lot of parts, you can make a round, use one tool on every part, and do another round with another tool. Of course this only have sense if you don’t have an automatic toolchanger.

Cons: Setup time: you need to cut a piece of wood squared enough, and glue to your wood. Also, if you make “rounds”, re-clamping can time consuming and, depending on your setup, prone to positioning errors.

Base block and screws

Here you machine a piece of wood and use some screws from below to secure the part. The block itself should be bolted to the tooling plate (or held on the vise). If your part has some straight holes you can look for a wood screw that thread on that hole without damaging it. I use this method for a second step on some parts clamped on previous ways (you can see the remaining of the disposable block on the back of the picture). This is the method I’ve used on my last video.

Pros: You can get a very precise positioning with the proper setup (e.g. using index pins). You can also clamp several parts at time.

Cons: Making the base block can be time-consuming. Also, you need holes where you screw can attach to, or you would need to make some holes on your part if you don’t have enough or appropriate ones.

As a final note: wood is a nice stuff to work with, but you should be careful and plan ahead your cuts to avoid tear out.