Air Coils

One of the most basic parts of many flight instruments is a device called an Air Core.  Air cores can move indicator needles of various types to a specific position based on two input signals that are 90 degrees out of phase, a sine and cosine wave.  The relative strength of these two signals determines the position of the indicator.

Mike Powell, the author of a now out of print book on building simulated flight instruments has a web page dedicated to construction of air cores: http://www.mikesflightdeck.com/instruments/diy_aircore_instruments.html

In looking at Mike's work in light of today's opportunities with 3d Printing, I came up with a nearly identical design for a hand built air core.  This so far untested design was created using a free account at Onshape.com and can be viewed using this link.

https://cad.onshape.com/documents/bdb91a1db5071919b3f06d12/w/1df14a84c751a7ce78a21975/e/d75c2da92298d8f9ce8b478c

At this point I am just beginning construction, so the design may change.

Like Mike's design, the mine fits inside a 1" long piece of 1" EMT tubing.  Some minor adjustments will be needed because some of the parts will be slightly different.  The Armature of the air core will be 3d printed.  I'll be using a slightly larger piece of Music wire for the shaft.   Mike uses Brass for the bearing at the front and rear of the shaft, I'm going to try nylon instead.

I'll be trying to drive the device with an arduino and an H-Bridge.  No doubt I'll be getting a lot of help with this part of the project.  I also expect to learn a lot more about electronics in the process.

I've joined the local Framingham, Ma - Makerspace to get access to various machine and electronic tools. 

Parts:

1" EMT
9/16 Brass Tube
Armature (3d Printed)
38 AWG magnet wire
.032 Music Wire
1/4 Nylon Rod
Tubular magnet magnetized across the diameter
1" fender washers (for additional shielding)



The first 3D printing of the armature was less than spectacular, but the Outer housing came out great.

Lessons learned:

• Printing took 1:30.
• Kyle Rivers at Framingham Makerspace advises trying slower print to get the small features to come out better.
• Since the center of the armature came out well, try making the armature as stock, without the cuts for the winding at the top and bottom.

• The outer housing was made using a band saw for the initial cut, with the first edge milled flat on a lathe.
• The second edge was cut 60% on the lathe and finished with a hacksaw.

This Blog follows: The Flightgear Wiki - How to Build Your Own Panel or Cockpit