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Guest MikePowell

Simulated instruments using RC servos

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Guest MikePowell

All,There are some additions and modifications to the DIY instrument pages on my site. The new material is about a third of the way down this page: www.mikesflightdeck.com/DIY_servo_instruments.htm and includes pictures of an RC servo based attitude indicator and combined localizer-CDI.Mikewww.mikesflightdeck.comInfo for simpit builders.

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Mike, thanks for the update. You're just full of good info. You've helped me quite a bit, directly and mostly indirectly. THANK YOU!

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Mike,TWO THUMBS UP!!! Thank you for such a wonderful information about those motors and RC controller. I could use that motorized potentiometer for autothrottle control. But my concern is... would that potentiometer still do function even if I disengage autothrottle (which means motor would not be running at all)? If its a possible to have motorized potentiometer for autothrottle would the motor be strong enough to do push and pull the throttle handle? I suppose, if I did not use motor as in autothrottle, but push the throttle in full and whenever I am ready to enage autothrottle would the motor know where the precise axis and control it? I assume it is at weight of at least 4 oz (made of wood and aluminum rod). How much capacity could the motorized potentiometer be able to do the function? If I am able to connected up with PIC16F628 "motorized potentiometer controller" how can I program it? any idea?

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Hi Mike.Great pics. Have you given any thought to using the synchro resolver to drive the compass ring? I have several, but I don't know much about them or how they work.Regards,Jim

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Guest MikePowell

Arthur,The motorized pots are light weight units with just enough torque to turn the knob. They don't have the horsepower to move a throttle mechanism. Still, you could use the concept. A motorized pot is simply a geared down motor with a slip coupling to the pot. You could build something similar with two disks pressed together with springs. One disk could be part of the throttle, coupled to the pot. The second disk could be coupled to a motor. If the motor were energized it could move the throttle, but moving the throttle by hand would make the two disks slip against each other. Since the host PC would both be running the auto-throttle routine and reading the throttle position, most of the software complexity could be written in C or VB and execute on the host. Electrical control of the motor could be through two binary outputs, like from an EPIC lamp driver. Use one bit to turn the motor on and the other to set the direction.I haven't made any throttles, so please understand I am shooting from the hip and take this with a large grain of salt.Mikewww.mikesflightdeck.comInfo for simpit builders.

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Guest MikePowell

Thanks for the kind words, Matt.Mikewww.mikesflightdeck.com

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Mike, Actually, I was looking for space available for autothrottle, I thought maybe using motorized potentiometer would be the best solution. But I guess it wasn't afterall since you said it does not have enough torque to move the throttle mechanism. Might as well, I would move on to the second option, using Junji's idea.. like you indicated using EPIC lamp card which is known as output module card if I am correct. But due to my concern, I have a 12 volt DC motor that has 2 terminals assumed it has to be + and -, through the EPIC card which one would be used to turn the motor or set the direction? and to confirm programmingI would either ask Ralph Robinson, Junji Hiryama, or Marc (EPIC MAPPER) to provide assistance. On other concern, since I am not an engineer, how could I just calcuate the ratio of turns, number of gear teeth which would be used for 100K ohms potentiometer and other one that would attach to throttle rod? To let you know, I have a 12VDC motor that already have 10 gear teeth and it is about size of 3/8. (I could attach you a picture of motor with measure tape if you want to) I am planning to have it set at idle to full trust at distance of 8 inches, would you happen to know which kind of gear teeth would do those function?Let me know

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Guest MikePowell

Hello, Jim,Resolvers are intereting little beasties, aren't they? They practically beg for someone to make a project using them. I have a couple of synchros, but haven't pursued using them. RC servos and stepping motors are just too easy to use. As it turns out though, my issue with the compass ring is basically a mechanical one. The ring has to be supported and be able to freely rotate while having the localizer and CDI needles poking through the hole in the middle of the ring. Further, the ring has to mechanically couple without slippage to some sort of position sensing device, such as a resolver or rotary encoder. Things just started to get a bit too complex and requiring too much precision construction/costly parts.Any thoughts?Mikewww.mikesflightdeck.comInfo for simpit builders.

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Guest MikePowell

Arthur,You have a number of interesting questions. Unfortunately, they are pretty much outside my area of expertise. Electronics I can generally comment on, but as the questions get deeper into mechanical systems, I find I must defer to others.Mikewww.mikesflightdeck.comInfo for simpit builders.

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I know, mechanical stuffs isn't my things either... Only other options is to go for a reserch, and if I find something better and something very interesting I will share it out with you... Thanks anyway.

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Mike.I'm asking questions that are WAAAAAAAY beyond my capability at the moment, but how do you interface these beauties to the comp and FS2002?I read on your site that you use a board that goes to the serial port, but what makes FS talk to the port? FSUIPC?Thanks in advance. I'm hoping to understand all this in say, oh, twenty to twenty five years. :-)

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Guest MikePowell

Whoops! I've been found out. Time to roll out the smoke and mirrors. (Anybody got a spare can of vaporware I can borrow?)This is a topic I do not as yet have a firm grasp on, but here's the game plan...There are two basic paths I will develop. One is based on a very simple circuit that converts a control voltage, say 0 to 5 volts, into the pulse format that the RC servos expect. This is a fairly generic solution and would require the use of a digital to analog output from the host, such as an EPIC gauge module or one of the Weedtech interfaces. EPIC already comes with hooks to MSFS (I think) so that solves the problem for this approach. Using a Weedtech or other vendor's output card would get the instruments interfaced to the PC but a software link would have to be developed to tie into FS.This first path is cheap if you already have analog outputs, but doesn't support complex behavior in an instrument. It's also not so cheap if you don't have analog outputs. So segue to the second approach...The second approach is based on a PIC16F628. These little beasties are cheap and relatively powerful. They can drive the servos (or stepping motors, or dc motors with a bit of power buffering), the seven segment displays, interface to a rotary encoder, support a serial com port connection to the PC, in addition to having enough horsepower left over to let the instrument display complex behavior without requiring a resource-hogging ddriver on the PC. So this second approach gets to your PC but, as you so rightly determined, not into your sim software.There appear to be two viable approaches to making this final, software connection. The MSFS panels and gauges SDK mentions proxy variables that can be read for use in controlling add-on gauges. So one approach is to write code that executes as a "pseudo-gauge", reads the appropriate proxy variables, then sends the needed control information across a serial com port to the instrument cluster. Each instrument has two IDs. One is common to all instruments and is used for global commands like reset. The second ID is unique to each instrument and is used to command individual instruments. This allows all instruments to be controlled through a single com port.Please note that the above paragraph has a serious smoke and mirrors quotient. I have read parts of the SDKs but have not written any code to try this technique. (But it sounds good, doesn't it??)The other technique, which is probably easier, is to use FSUIPC. I've made about as much progress with this as I have with the MS SDKs, so we're still talking smoke and mirrors at this point.To date, I have written ("hacked together" is more discriptive) a very basic windows app that gives me a dialog box I can use to send test data to the instruments. I am just about to add the capability to read back from the instruments. (The VOR/Loc CDI OBS value has to be read back, plus it's nice to read the revision level of the instrument firmware.)I really need to spend the time on the host PC software, but I really, really like building things.Mikewww.mikesflightdeck.comInfo for simpit builders.

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Hi Mike,Thanks for the update again. I'm really enjoying following your work on these instruments. Is the book your final goal or are you planning on selling the working instruments too?Peter http://bfu.avsim.net/sigpics/PeterR.gifBFU Forums Moderator[table border=2 cellpadding=0 cellspacing=1][tr][td][table border=0 cellpadding=8 cellspacing=0][tr][td bgcolor=#540000]http://bfu.avsim.net/sigpics/logo75t.gif[/td][td align="center" bgcolor=#FFFFF6]Bush Flying Unlimited"At home in the wild"Looking for adventure? Come join us! * [link:bfu.avsim.net|Web Site] * [link:www.cafepress.com/bfu,bfu2,bfu3,bfu4|BFU Store] * [link:bfu.avsim.net/join.htm]Join!][/td][/tr][/table][/td][/tr][/table

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Guest MikePowell

Good Morning, Peter.The thought is to offer the book, blank PC boards and programmed PICs. The book is to be self contained with complete schematics and source code, so the reader really won't need anything else. Still, having them makes building the projects easier and faster.I don't plan on manufacturing them myself. Too lazy. Besides, if this one covers its costs, I have ideas for two more.Mikewww.mikesflightdeck.comInfo for simpit builders.

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