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Fast Times at Marginally Clever

I’m working overtime right now and loving every minute. Today the 3d printers are running, the laser cutter is running, and two Makelangelos are drawing sample pictures for the Vancouver Mini Maker Fair this weekend. There’s going to be a workshop to make line-following robots (so nervous, so excited!), first view of a new kit, the 3-axis arm, and the prototype of the 5-axis robot arm will be there. This is also the first year I’ll have help at the booth, because we’re growing like crazy here. I’ve just received the new Marginally Clever shirts and they are suh-weet. So sweet I might just put them up for sale.

Next week I’ll finally be able to take a breather and then I can start prepping a slew of new products (parts, not kits). I calculate I’ll run out of stepper motors in about two weeks and then I’ll have a 2-3 week period where I can’t ship the related kits, so I’ll be investing the time on all the stuff I don’t normally do – like upgrading the website to be mobile friendly.

In about two weeks some of my code will be going to the White House. Yes, that White House. The GcodeCNCDemo was used in another open source project that has been invited to show their work to POTUS. Nice! I’m now 1 degree away from the oval office in two different ways.

All this success wouldn’t be possible without you, dear reader. Thank you for your continued support and feedback!

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New Forum for Educators

There’s enormous interest in using robots to teach STEM subjects, all the way from K12 up through university. I’m not a qualified teacher and I can’t handle all the email so I’ve created a section in the forums just for you beautiful, hard working people. Let’s work together to help each other!

Check it out

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Building a 5DOF robot arm 3

Here’s the latest on the 5DOF arm.

Tomorrow I’m preparing the last Makelangelo kits that will ship before the Vancouver Mini Maker Faire. I spent the better part of the day connecting the forearm to the bicep based on yesterday’s design. My design software crashed and corrupted a few files. Boo! I also experimented with limit switch positioning. I think the two opposite sides of the wrist are best – I can catch three different kinds of dangerous movement with only two switches. Plus the wires all run the same length, which makes them easy to measure and bundle together. The next time I rebuild the arm I’ll have specially placed holes for flawless switching.

Am I starting to experience diminishing returns? The tiniest change can have a trickle down that affects 4 or 5 laser cut parts. I’m resisting the urge to scratch at parts of the design that “itch” but still work. I tell myself they’ll get better soon enough. Keep your eye on the prize.

I can see how the shoulder and the base should look in my mind’s eye. Just like the switches it will take a few iterations to work out the details. I’m a little excited by the idea that I might not have enough power to lift the arm. What if I have to print a whole gearbox? Can I do it? How long would it take? It seems like a judicious combination of bearings and gears, both of which I’m learning about quite a lot these days. Heh – I thought these were good minecraft blocks, but it turns out maybe I can put them together to make an even better block.

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Wearable robot arms for those times when you need a helping hand

Supernumerary Robotic Limbs (SRLs) give you that extra hand when you need it. There’s also a version with arms at the waist. Find out more in the
IEEE times article.

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Building a 5DOF robot arm 2

Here’s a shot of my workbench right now.

I went through three different wrists before I got the measurements right. The bevel gears were brushing against the forearm or the mounting screws. I also reprinted the wrist gears with a smaller center hole so they can hold the 5mm bolt that runs across the center. I need to find a way to attach that bolt to the wrist. A nut, a lockwasher, and another nut? Double nuts? Seems to work on the Prusa 3D printer hobbed bolt.

In the next version the elbow joint will change to increase the range of motion. In the current version there’s little or no room to add braces across the bicep pieces. Braces are needed to keep the bicep from twisting along it’s major axis. I haven’t worked out how to drive power to the elbow rotation yet. I’d like to put the stepper motor down at the shoulder again, but I might have to put it up near the elbow. Try it and see!

I’ve also started to plan the limit switches. In the Arm3 the switches are very close to the shoulder. There is less opportunity for error the further out they move. An error of 0.1mm near the point of rotation can turn into many mm out at the far end.

The total length of the forearm is something like 235mm. Once the tool changer goes on the end the distance from elbow to tool changer will be 250mm.

We got a mention in MAKE at the tail end of Robots Week. Thanks, Caleb! Please keep sharing with your friends. All my marketing is all done through word of mouth – usually my own. Your help drives sales, which gives me the resources to keep designing.