[simpits-tech] Driving Resolvers

[Marv De Beque]

Okay, my limited knowledge of resolvers is that it is a mechanism to 
read the position of a shaft.  I think you have a synchro.

A synchro can probably drive an ADI since they use precision bearings, 
but it might require a little current.

Here is a portion of my Syncro 101 post:

"A synchro is essentially a compass needle with two electromagnets 
located at the perimeter of the needle, one at the North pole and one at 
the East.  By varying the magnitude and the polarity of the current 
induced in the two electromagnets, you can make the needle point 
anywhere on the dial!  The two electromagnets are fed voltages that are 
multiplied by the  sine and the cosine of the desired angle which you 
want the needle to point.  If you feed the two electromagnets AC signals 
that are 90 degrees out of phase the needle will spin, completing one 
revolution for each cycle of AC.

You can also reverse the process and induce two AC signals with a 
synchro and use it as a means to indicate the rotational position of an 
object.  "Note: this is a resolver."

Another issue for the synchro is the interface.  There are chips made to 
do this, but they cost about $100.  A hobbiest can roll their own.  You 
simply need two digital to analog converters and a small 
microcontroller.  The micro would contain a sine lookup table and could 
translate a digital value (say for instance, fuel quantity) to the two 
digital equivalents which are then output to the two digital to analog 
converters that feed the synchro.  You need a good set of digital to 
analog converters with enough resolution and speed or it will look like 
a stepper motor when it moves.  You can add a small capacitor to the 
outputs to take some of the edge off of the movement."


As you can see, rolling your own isn't that hard.  I haven't tried it 
yet, but I probably will (in between making knobs, and a half dozen 
other goodies for you guys).  If I get a design I like, I will share it 
with you.  Basically, a small micro like a Basic Stamp might do the 
trick.  If you can get a 10-bit Digital to Analog converter cheap enough 
(actually, two) you can make the interface.

I don't know how your ADI is built, but you need to get an interface 
specification for it if you have any hope at all of making it work as it 
was originally designed.  You may find that a significant challenge in 
itself.

On a related subject, I just ordered and received a mico-servo to play 
with for analog gauges.  Using some gearing I can make a full 360-degree 
rotation, but that will not work for an ADI unless you never do 
aerobatics.  ;-)

However, the basic gauge module I have in mind, if I succeed, will be 
able to drive any of the 9 other gauges used in the F-16.  I plan to 
make a 1" diameter module that will accept any size "head" to make the 
finished gauge.  The reason I like the servo solution for the other 
gauges is it a simpler interface solution that is affordable.

Marv

On Thursday, March 28, 2002, at 09:53 AM, Ken Trager wrote:

> Well, I took the dive and brought a ADI out of a DC-10 for my KingAir 
> Sim.
>
> Question is - after looking at Matt Wietlispach's webpage
> http://members.aol.com/wietlpachm/howto/technical.htm
>
> There is got to be a way of doing it- Matt is doing it but HOW??
>
> Is Matt out there in SimPit land?
>
> His webpage does not show what he is using to convert digit into 
> resolver signals.
>
> Gene - I got an absolute encoder to work on the back side of the VOR. 
> Thanks - it is easy
> -
> it is using a 9 bit data bus with BCD code. The signals go into the 
> serial port and VB
> picks
> the number - i just have not wrote the code to write to FSUIPC.
>
> Back to the resolver - someone back a couple weeks said that resolvers 
> have little torque
> and
> to use a stepper motor - The ADI uses resolver for both Roll and Pitch 
> so I am going to
> stay
> with that. It will save me some time by not ripping the damm thing 
> apart and putting in
> stepper motors.
>
> Any ideas out there -
>
> Ken Trager
>
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