AeroPac Motortube Modification: July 2011

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This workflow illustrates a method for modifying a motor mount assembled <br />from instructions for a PMR retainer, so it can accomodate <br />a required AeroPac retainer instead. The motor tube was initially extended only 3/16" beyond the centering ring. <br />The AeroPac retaining ring requires a depth of twice this, or 3/8". A dremel tool is set up on a drill press at 90deg, and braced against the <br />base of the airframe jig using two adjustable cross pieces. This allows <br />for precise alignment of the cutting bit next to the motor tube and <br />ensures the drill doesn't move while the airframe is rotated. The cutting bit just needs to graze the motor tube, and cut into <br />the centering ring to a depth of about 1/4". A shop magnifying glass allows for detailed guidance of <br />the bit, and protects against flying debris... after the first hole is cut, the airframe tube is rotated slightly <br />and additional holes bored out in turn... With minor adjustments, it's possible to maintain consistent and <br />accurate progress around the motor tube... nearly around the entire circumference... The completed cut... The motor retainer now slides on the full 3/8" depth <br />and rests flush with the motor tube. The next step is to epoxy the retainer in place with J-B Weld, and then <br />fill in the gap left by the cut. This will also strengthen the <br />centering ring against the retainer. The motor tube after two applications of JB Weld were applied to <br />fill the gap, and then a layer of epoxy putty applied to taper the <br />bulkhead into the motor tube.