• Three point clamped wedge secured laser cutter joinery

    03/29/2018 at 03:04 0 comments

    On a few occasions I have had the need to secure something to a flat bit of laser cut wood. In all cases, I created precise shapes that allow me to rigidly and accurately grip the object while not depending on the exact dimensions of the cuts themselves. The method requires final alignment to be performed during assembly, but does allow for post-assembly re-alignment and doesn't require any adhesives or fasteners. A few examples from a recent #NeuroBytes patellar reflex model iteration:

    The top image is a simple T-joint, used to connect two right angle bits of 3.2mm aircraft plywood. The middle piece goes through the base in two spots and has cutouts for wedges, which are inserted and tightened during assembly to pull the joint tight. The angle isn't exactly 90 degrees due to the aforementioned kerf taper, but it works well enough for this application (a mounting plate for a demonstration model).

    The lower images show a second joint from two sides. In this case, I needed to precisely locate a Touch Sensory Neuron with respect to the patellar tendon (the blue wire and O-ring assembly). I didn't want to modify the circuit board at all, and the exact orientation of the snap-action switch at the end of the PCB is critical to proper functionality of the model. Since the tendon is made by the end user and may vary slightly in length, part of the leg adjustment process requires the switch orientation to be adjustable, lockable, and potentially re-adjustable down the road. A cross plate with a few machine screws would have done the trick, but this method avoids the need for a screwdriver and easily lost hardware. I call the weird curved clampy bit the 'connector plate'. Not a great diagram but hopefully you get the idea. The wood base has several layers, and you have to imagine that the leftmost layer extends out towards the viewer along the dashed line. That way, when a wedge is inserted into the rectangular 'wedge goes here' slot, it pushes the upper bit of the connector plate to the left as its driven into place, clamping the board securely in place. I really should reference a side view or 3D model with this sectional image, but... here we are.

    During installation, the connector plate slides in from the bottom (which is open and rotates into position, pivoting on the lower 'catch'. To ensure clearances with the holes in the wood base, I keep track of the connector plate's position extremes on the wood base using guides in Inkscape. Rotating the connector plate like this is a synch if you just move the cross symbol to change the center of rotation to the bottom contact point:
    Note that in the third frame, I actually translated the connector plate up a bit so one of the corners can clear. This is much easier during real life assembly; you really just need to be sure everything clears at all points during the rotation/translation, as manual assembly makes combining both movements quite intuitive.

    I used a similar method to hold the servos on for the latest NeuroBuggy design. Again, I needed to secure an object (in this case, a continuous rotation servo) to a flat laser-cut sheet. The object needed to be adjustable (toe angle!) and quite secure, but also removable. The connector plate is bigger but otherwise similar to the previous example -- it slides in from the rear of the car, rotates into position, and gets secured by a wedge:

    This method is still very much a work in progress. I think a lot of optimization could be done to reduce the material requirement and cut length; for example, the width ratios of the tenons and slots could be standardized (probably based on a woodworking joinery book's advice), and the curved shape of the connector plate itself could probably be generated parametrically once a few constraints are figured out. The wedges are also probably beefier than needed and the angles could be optimized. But it's a good start -- feels good to assemble something without glue or fasteners!

  • I've got extra time in a 10m EMC test chamber next week!

    02/09/2018 at 21:07 3 comments

    [EDIT: I didn't have the form configured right and folks couldn't access the questions. That has been fixed, so try the link again!]

    We're headed back for #NeuroBytes EMC testing next week (unintentional radiator) and the chamber requires a 2-hour minimum reservation. If you have a project that you are considering commercializing, I'll run a pre-test scan for you FOR FREE! Some requirements:

    • I prefer to only work with open source projects, and I want to share the results publicly. EMC testing is expensive and mysterious (at least for hobbyists), and building a public record of known-good / tested boards would be a great thing for the community.
    • Time is short. We are looking at Friday, February 16th, at 8AM in Minneapolis, MN. So you need to be ready to ship your project to me NOW.
    • I will need you to provide a self-addressed and postmarked envelope for return shipment.
    • Tests sweep from 30 MHz to 1 GHz. Standard unintentional radiator stuff. That means no radios -- ESP32, ESP8266, Bluetooth, Wifi, etc. Sorry folks.
    • Your project needs to set up and tear down quickly. As in, I plug it in (or insert batteries) and put it in the chamber, and we go. 5 minutes max.
    • This is just a pre-test -- you'll get a report but it won't give you certification.

    If you're interested, fill out this Google Form and we'll start the conversation. Again, time is of the essence here.



  • How To Fix Your Broken Onion Omega2 Board For Only $3.20

    02/03/2017 at 16:26 8 comments

    Yes, it is broken. Step One is to accept this fact:

    Above: a $5 Linux computer that uses 2mm header pins, meaning it requires a $10 - $15 dock to use.

    Step Two is to bitch about the problem on Hack Chat (you have to scroll back a few weeks to see the post). Half an hour later, be gracious when @davedarko throws together a quick PCB design and sends you the @oshpark purchase link. Get stoked and order the boards immediately (including one free!):

    Step Three: wait two weeks, find an envelope in the mail, snap apart a header, solder 64 thru-hole joints, and be excited that you saved money:

    Yes, it fits -- the board straddles half a breadboard and gives you plenty of space to pick up all 32 pins. @Onion.io: please consider changing to 0.1"/2.54mm headers like the rest of the world for your next spin, it wouldn't change the board dimensions by much and would make your product substantially more user-friendly!

    Thanks again, Dave!