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New robot arm with BlocklyProp (documents online) — Parallax Forums

New robot arm with BlocklyProp (documents online)

Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
edited 2020-04-04 02:35 in Learn with BlocklyProp
I was tasked by the local high school to design a robot arm for their robotics class. The idea was that all the custom parts for it could be cut out on the class laser cutter and assembled by the students using stock fasteners, motors, and controller. Here's a photo of the completed prototype:


Constructed of 1/8" MDF and acetal copolymer, it has has three controllable axes with a manually-adjustable wrist joint. The controller is a Parallax Activity Board. The three axes are driven by Parallax Servo 360s, which are externally geared down to provide more torque. The gripper, which can be removed to allow other kinds of end effectors, is driven by a cheap 9G servo from HobbyKing. The Z-axis bearing is a cheap 4" lazy-susan ball-bearing unit from McMaster-Carr. The arm bearings consist of acetal sleeves riding on shoulder screws. There is no friction against the MDF to cause wear. Once I was happy with the design, I wrote an assembly manual (too big to attach, unfortunately) so the students could assemble their own arms from parts they cut on the laser. The CAD files for the arm parts are in Rhino3D format, although I actually designed them in CorelDraw.

Once I had an operational arm, I had to come up with some driver software for it. Since the class has been using BlocklyProp, that was an easy choice of platform. But, boy!, was I in for a learning adventure! I had never really used Blockly, so had to learn that (which was really easy). But I wanted custom blocks just for the robot, and that's where things began to get complicated. However, thanks to some amazing and incredibly patient and generous support from Matt Matz, along with some custom Blockly internals he provided, I was able to create custom blocks and get them into the toolbox. The driver software is written in C -- not my favorite language by a long shot, but more than adequate for the job -- and ported to my Blockly Solo repository on github, from which it runs -- another learning adventure. Here's a screen shot of BlocklyProp with the robotic arm tool flyout from the toolbox:


I still have some servo driver issues to fine tune, but the arm looks like it will perform well in the class (assuming classes in Washington State start up again before June). Once it has been proven in the classroom, I'll post the CAD files, a bill-of-materials, and other documents here in the forum.

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  • Wow, Phil, this is a great outcome. Is your version of BlocklyProp a custom stand-alone, or are these PTHS Robot Arm blocks enabled by choosing a particular board type?

    I'm looking forward to seeing this arm in action. I noticed you built in some really nice design concepts with geared-down motion control and Feedback360 servos. I'd like to put one on my laser cutter, too.

    Ken Gracey
  • Thanks, Ken. At this point the arm blocks are restricted to the Activity Board, but available to any project that uses it. There's a lot in the driver software that's particular to this arm design, including port assignments. The assembly manual shows where each servo and feedback wire is to be connected, in order to agree with the port assignments. The motor dynamics are pretty particular to this robot, too. I've spent a lot of time tweaking them, and they're still not quite there yet. At this point, all three servos use the same settings. But the arm servos are sensitive to static loads, while the Z-axis servo is more sensitive to inertial loads. So I may need to address them separately.

    The Blockly Solo software can be accessed from my repository on github. I'll email you the address so you can play with it if you like.


  • This is a really amazing project, and it's been fun to watch how this project has evolved over a few years. I first met Tim B. (who teaches robotics at PTHS) when I did a educator training in North Seattle. He brought one of the first versions of the robot arm and it was fun to learn about his goals and what he hoped his students could learn from it in his classes.

    What I like second most (because the thing I like most is that kids are going to learn some really cool stuff from this) is that this is a really great example of how the fact that BlocklyProp is open-source, which means it can be remixed and leveraged in some very cool ways. As Parallax moves from the original version of BlocklyProp to the new version called Solo (, making a fork of the project and putting it up on a website of your own isn't actually that hard to do. The code runs entirely in the user's browser (Chrome, Firefox, or the newest version of Edge, and I think even Safari works), so you don't even need advanced features for that hosting. Just put up the files and let it go.

    Phil is right in that the learning curve is pretty steep, but if you're up for the challenge, there are some great resources out there. If there is enough interest, I could even do a video that would be like a "tour" of the codebase for BlocklyProp.

    Because it's open-source, there are opportunities (and a need) for power users to contribute. One of the biggest needs is actually propeller c libraries for devices - for example, we don't have a prop-c library for a real-time-clock (RTC) module/chip, or for one-wire devices like Dallas thermometers, or "DotStar" RGB LEDs. There is a good tutorial written by Andy Lindsay on how to create a propeller c library on, and it's something we could really use some help on.
  • WhitWhit Posts: 4,191
    @"Phil Pilgrim (PhiPi)"

    Incredible work Phil - You never fail to amaze me with your creativity and innovation. I wish I lived close enough to be in your class!

    Hope you are well. Stay safe.
  • Thanks, Whit!
    Hope you are well. Stay safe.

    You likewise.

  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2020-04-04 02:27
    The robot arm stuff is alive now, but still very beta. To access the documents, including a build manual, programming manual, an Excel BoM, and laser cutout CAD files in Rhino3D and CorelDraw formats.:

    To use the special version of Blockly:

    To access the svg files referenced in the docs:

    The format is totally 1990s primitive, but the stuff is all there. I'll try to prettify things later.


  • WhitWhit Posts: 4,191
    Thanks for your generosity and creativity, Phil!
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