Testing rig upgrade II

This is a follow up on an original article Testing Rig Upgrade, as it just keep going!

Ad the first thing, I have to admit that those rubber-bands were not good enough. I’ve left our model hanging there for a week and they got loose (with a great help of Queensland summer temperatures as well). So they’ve got replaced by springs.

You may wonder why two types … because that C-161 wasn’t strong enough, so I had to upgrade to C163s! All values below are in imperial units – but I suppose it is clear C163 are almost 3-times stronger than those C161s.

Specifications for the Century Spring C-161 Extension Spring

Part Number:C-161
Manufacturer:Century Spring
Ajax Part Number:50161
Spring Type:Extension
Material:Galvanized Hard Drawn
Wire Size:0.035
Body Length:1.875
Max Ext Length:5.900
Spring Rate:0.5
Max Load:3.3


Specifications for the Century Spring C-163 Extension Spring

Part Number:C-163
Manufacturer:Century Spring
Ajax Part Number:50163
Spring Type:Extension
Material:Galvanized Hard Drawn
Wire Size:0.047
Body Length:2.626
Max Ext Length:3.600
Spring Rate:2
Max Load:8.4

In a next stage I’ve decided to somehow reorganise all the wiring and amplifiers, so they are all not hanging there in the air. That already proven being a bad idea as I’ve damaged couple of those cells in a irreparable way.

The first was a set of load-cells clamps.

Their design was quite trivial.

module pcb_cutout(z) {
  cube([21, 2.3, 39], center=true);

  //space for pins etc.
  cube([18, 12, 37], center=true);
  //slide for a chip on a side
cylinder(39, d=3, $fn=3, center=true);

D() {
  union() {
    //pbc + meat
    minkowski() {
      cube([45.2, 3, 36], center=  true);

  //pbc cutout
  pcb_cutout( 12);

  hole_size = 3;
  T(12, 0, 1)Rx(90)
cylinder(15,d = hole_size, center = true);
  T(-12, 0, 1)Rx(90)
cylinder(15,d = hole_size, center = true);

And they come up nicely.

Well, rainbow data cables needed some clamping as well. I’ve printed a set of very simple L-shapes to hold those well.

Another step was to get some nice box to hold our RaspberryPi. I’ve been lazy to start designing it myself so I’ve simply downloaded Raspberry Pi 4 Case, active cooled with wall mount from someone with nickname tipam and which looked pretty cool on a picture.

Mainly it came with a promise of a wall – mount, which honestly needed some more love and I actually ended up tweaking it myself to fit the testing rig beam. It all still worked out very nicely.

Final touch was a set of screws to reduce a surface area between the load cell and our cart. Serge sharpened them for me and here they come mounted.

Then I spent three weeks developing an app which would visualise readings from all those load cells.

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