RC13HighStrengthEncoderWires

Overview

In the past, there have been cases of encoder faults being detected due to encoder wires breaking. The terminals in use are the Molex 1.25mm pitch Pico Blade terminals (encoder side) and the Molex 2.00mm pitch Sherlock terminals (board side). Four of these signal wires are bound with heat shrink tubing to create each encoder wire.

Problems and Possible Causation

• The wires tend to break near the encoder side (connector terminal breaks off)
  • Imperfect wire stripping causes poor crimping, making the connector very fragile
• Wire tends to break on disconnect
  • The older revision E4P encoder used a through-hole version of the mating connector, which made disconnecting of the wire very difficult
    • E4P encoders manufactured after 11/29/2011 have the surface-mount version of the connector (signifcantly lower connection resistance)
  • High connection resistance and small room for handling the connectors required inevitable improper methods to be taken to disconnect the wire (partial tugging on the wire itself)

High-Strength(HS) Prototype

Goals

• Strengthen the encoder-side connection
• Allow the wire to be safely disconnected by tugging on the wire assembly

Assembly

• Cut off a short length of excess leads from through-hole mount components (e.g. IR LEDs, photodiodes, buzzer, etc.)
• Crimp an encoder-side terminal on the lead
• Solder on a length of stranded wire on the lead+terminal (make effort not to have sharp points around the solder joints)
• Place the lead+terminal+wire in an open slot in the encoder-side conenctor housing
• Put on a short length of thin heat shrink tubing on the lead+terminal+wire to cover the exposed metal (to prevent shorts between the signal wires when bundled)
• Repeat the above steps three more times using the same connector housing
• Strip off a small segment of the insulation and crimp on the board-side terminals on each of the four wires
• Use a larger diameter heat shrink tubing to bundle the four wires
• Put on the board-side connector housing

Results

• After 50 connect/disconnect tests (wire-tugging), the encoder wire assembly maintained functionality
• Crimped terminals do not slip off of solid-core wire (unexpected)

Issues

• Takes a long time to assemble
• No consistency in the quality of recycled parts (although the two prototypes were functional)