Fix spring dimensioning calc error

We have 4 springs, so the effective spring constant is 4 times higher.
Reflect this in the calculations and adjust the CAD model for the
updated spring length.

Spring-Dimensioning.ipynb

@@ -2,7 +2,7 @@
  "cells": [
   {
    "cell_type": "code",
-   "execution_count": 17,
+   "execution_count": 1,
    "id": "5bef2913-4855-471d-9594-5ec45c029048",
    "metadata": {},
    "outputs": [
@@ -10,8 +10,8 @@
      "name": "stdout",
      "output_type": "stream",
      "text": [
-      "Length: 236.9 mm\n",
+      "Length: 143.2 mm\n",
-      "Freq:   1.411 Hz\n"
+      "Freq:   2.822 Hz\n"
      ]
     }
    ],
@@ -19,7 +19,7 @@
     "import math\n",
     "\n",
     "# Parameters\n",
-    "spring_constant_n_mm = 1.1\n",
+    "spring_constant_n_mm = 1.1 * 4\n",
     "spring_length_resting_mm = 112\n",
     "\n",
     "def spring_length_at(weight):\n",
@@ -39,7 +39,13 @@
    "cell_type": "code",
    "execution_count": null,
    "id": "f21d84d9-c7a1-4fd2-aa32-136f04db32e5",
-   "metadata": {},
+   "metadata": {
+    "editable": true,
+    "slideshow": {
+     "slide_type": ""
+    },
+    "tags": []
+   },
    "outputs": [],
    "source": []
   }