Avionics Bending: Mechanical Synchro Signal Producer (Part 1)

Components for the initial Synchro Transmitter Controller

Today, I am embarking on a project to build a mechanical Digital to Synchro converter. Digital to Synchro converters are, of course, available in the form of very very expensive solid state devices form companies like DDC or other. However, for the L-1011 project I don't have the financial resources to purchase several of these devices to address all of my synchro signal needs. If you remember, synchro transmitters produce a 3 phase signal that is created form a single 400Hz 26V AC reference signal. The 3 phase shifted signals encode the angle of the synchro shaft. This technology has been around for a very long time and was, and in many cases still is, the standard for transmitting shaft angle between components.

For example, on the L-1011 the airspeed indicator and the mach number are both transmitted form the transducers to the cockpit instruments as 3 phase synchro signals. If you want to read more about Synchro Transmitter, like the ones I will be using to build this first prototype with, you can read about them here.

To build this first prototype idea I will create a mechanism for a stepper motor to drive a synchro transmitter. I will print the components using my Makerbot 3D printer and since none of the components need too much rigidity for the initial testing I will print them in PLA. I will use a Be able Bone Black as a way to drive the stepper motor and to read the Zero point on the Synchro. My initial idea is to zero the synch by using an indexer on the synchro gear.

PLA printed Synchro Gear with Indexer

The plan is to read the index with an optical switch.

I picked a NEMA 17 stepper motor not because they are needed to drive a tiny little synchro ... they are really an overkill and rather large ... but because I bought 50 of them for close to nothing on eBay.

I would very much like to make this an Open Hardware project and would like to invite you to participate in it. I am drawing the components in Autodesk Fusion 360. Please send an e-mail to curdzechmeister@gmail.com and I will add you to the Fusion 360 project.