title: struct.error: required argument is not an integer
body: <p>I have the following python code:</p>
  
  <pre><code>velocity = 0
  rotation = 0
  vr = velocity + (rotation/2)
  vl = velocity - (rotation/2)
  cmd = struct.pack("&gt;Bhh", 145, vr, vl)
  </code></pre>
  
  <p>I dealing with the following error:</p>
  
  <pre><code>File "control.py", line 125, in __init__  
  cmd = struct.pack("&gt;Bhh", 145, vr, vl)  
  struct.error: required argument is not an integer
  </code></pre>