Avionics Bending: Mechanical Synchro Signal Producer (Part 7)

Mechanical Digital to Synchro Converter - Test Assembly

Made lots of little tweaks to the individual parts and did a test assemble of some of the components. Eventually the entire assembly will be held together by four rods. Right now, I did a test assembly of the connector plate, the stepper motor plate, the synchro transformer plate and then the section that hold the electronics. Yep, those are cable ties holding the pieces together right now; however, I did this just to double check the sizing of the spacers and to make sure that the gear mechanism lines up.

Mechanical Digital to Synchro Converter

The image below shows the basic Beagle Bone Black in the the rear section of the design. There will actually be a cape on the Beagle that will handle the Stepper motor.

Mechanical Digital to Synchro Converter - Test Assembly

The images show the center core with the Synchro Transformer not yet assembled. I will try to get some rods over the next few days and then put the entire design together and cable it.

Mechanical Digital to Synchro Converter - Test Assembly

So far I am about $86 into this effort. Really want to keep it below $100 if possible. The most expensive part, so far, was the Beagle. Maybe in future iterations I go with a RaPi, but, actually both the BBB and the RaPi are a bit of an overkill for this.

Avionics Bending: Mechanical Synchro Signal Producer (Part 6)

Mechanical Digital to Synchro Converter - Connector and Electronics Bay

I added the connector plate and the electronics bay to the design. The Beagle Bone Black (BBB) will ride in an "electronics bay" on the backside of the design. This will be located behind the synchro transmitter. For the initial design there will be daughter board on the BBB driving the stepper motor (see image below). All connectivity, except for Ethernet, will be brought in through a Tyco Circular Connector. 

Mechanical Digital to Synchro Converter - Connector and Electronics Bay

The image below show the current design from behind. I envision a case around the complete design and a DIN rail holding bracket so that the unit, or multiple units, can be attached to a DIN rail in the simulator. The 26VAC 400Hz power sill also be brought in via the Tyco circular connector.

Mechanical Digital to Synchro Converter - Connector and Electronics Bay

Here is the left hand side view of the current design iteration. 

Mechanical Digital to Synchro Converter - Connector and Electronics Bay

Over time I will probably come up with a more space optimized design. If you have any design ideas please call them out to me. 

Avionics Bending: Mechanical Synchro Signal Producer (Part 5)

Mechanical Digital to Synchro Convert

Here is the first printed and assembled version of the mechanical digital to synchro converter motor assembly. It's a pretty simply assembly and together with the stepper motor and the synchro transmitter and the optical sensor I am about $22 into the project. In the image below you can see the proposed location of the optical sensor.  Next will be to design the plate that holds the Beagle Bone to drive the stepper motor with.

Mechanical Digital to Synchro Converter

Once I get a little further with the design I will put the CAD files on grabcad and the code on github. 

Avionics Bending: Mechanical Synchro Signal Producer (Part 4)

Mechanical Digital to Synchro Assembly

Here is the first design draft of the mechanical digital to synchro converter. The stepper motor on the bottom turns the Synchro Transmitter on the top of the design. The gear ration between the NEMA 17 motor and the Synchro should allow for very fine adjustment of the Synchro. The next rendering shows the the top plate and the Synchro Transmitter removed.

Mechanical Digital to Synchro Assembly

The picture below shows the assembly with the holder on the left hand side for the optical zero detection.

Mechanical Digital to Synchro Assembly

Another view of the prototype assembly from below. Here you can see the cutout for the NEMA 17 motor.

Mechanical Digital to Synchro Assembly

The entire assembly will be 3D printable. I will print the first prototype in PLA and then see how rigid the design is. The next step will be to add the design for the Beagle Bone Black holder and the 400Hz 26VAC  connections into the design.

Mechanical Digital to Synchro Assembly

Avionics Bending: Mechanical Synchro Signal Producer (Part 3)

L-1011 Project - Mechanical Synchro Converter

Modeled the motor and synchro components to go into the design. Here is how I currently envision the device to work .... it's actually quite simple. Above is a block diagram of initial idea for the device.

Let's take an example of the Airspeed indicator:

1. The device initializes by rotating the assembly until Zero Detection is reached. We have now stablished the starting point. 
2. Indicated Airspeed (IAS) is sent from X-Plane via UDP across the Ethernet to the Beagle Bone Black (BBB). 
3. The BBB translates the airspeed into angular information around the airspeed indicator dial. 
4. The BBB instructs the Stepper Motor Controller to move a computed number of steps forward or backwards. 
5. The linked Synchro Transmitter takes a 26V 400Hz input sources and creates the 3 Phase Synchro output needed by the L-1011 Airspeed Indicator. 

Avionics Bending: Mechanical Synchro Signal Producer (Part 2)

Mechanical Digital to Synchro Converter - Modular Mounting Plate Back

Mechanical Digital to Synchro Converter - Modular Mounting Plate Front

Working on the design of the motor mounting plate for the Stepper and the Synchro. This modular plate should accommodate a single stepper motor and a single Synchro Control Transmitter. The modular motor holder. I am also working on an alternate design that can accommodate the Coarse and Fine CTX for Altitude encoding. 

Once getting closer to a more practical design of the holder I will make it available as an Open Hardware project. 

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.

Avionics Bending: Digital to Synchro Conversion

Perhaps one of the bigger challenges in using older avionics is that most of them are deeply rooted in analog technology. More precisely, many avionics instruments form the 70s and 80s extensively use synchros and resolvers. Here is a picture of what a typical set of synchros in an instrument from the early 70s looks like:

Synchros are actually pretty old technology but are super resilient to noise and other external factors. They are still pretty common on just about all aircraft today, however, digital avionics have pretty much pushed them out of the cockpit. However, for the L-1011 sim project I will need a lot of synchro input to drive the avionics with. The good thing is that there are quite a lot of digital to synchro converters out in the surplus market that can be used for testing. The ultimate goal, of course, is to build some basic converters.

Below is a short video of my reference Digital to Syncrho converter. It's made by Shadin and actually designed to drive DME indicators ... however, it can be bent to control just about any synchro. It takes ARINC 429 data packets on one side and outputs an X, Y, Z synchro signal on the other side. What you see in the video is Label 251 data from 0 to 360".  The really tall wave (enlarged by a factor of 2x) is the reference wave, I use it to trigger the scope with. The two small waves show the phase shift on the X and Y phase: