DC motor Autothrottle

[Melnato]

Don't want to beat a dead horse or put Alan under pressure,
but Im wondering IF FS2Phidgets will provide a software solution to driving DC motors for Autothrottle.

I have seen several "work-around" solutions to this, but im still hoping for
a software solution.

Alan, if its impossible, that's cool...Ill get on with an alternative.

Thanks again,

Nat

[fordgt40]

Nat

What is the problem that you are seeking a solution for?

Regards

David

[Melnato]

G'Day David,

As yet there is no way (with Phidgets or any software I think), to control
the position of the DC motor when used for Throttle lever.

Unlike Servos which have a position sensor, DC motors can only be programmed to go forward and back.
If there was a way to use the analogue sensor connected to the levers in all TQ's to "tell" the motors when to stop and go,
like a feed-back loop, life would be easy

Nat

[fordgt40]

Hi Nat

I just picked up your reply before I turn in!

There is a way to solve your problem, by using pulse width modulation (PWM) to control the speed and direction of a dc motor, coupled with positioning via a potentiometer and software that can control it. There are a number of products/software that will do this and quite cheaply. It is now nearly 1am UK time, so I will provide the links and further info tomorrow.

Regards

David

[Ronson2k9]

I would be interested in finding this out to for the trim wheels I'm working on. This same concept should be applicable to that as well. For the autopilot is going to be moving the trim wheel. From what I've read about the trim wheel movement from one terminus to the other it's 8 revolutions of the wheel. So a servo couldn't be used to actuate the movement.

As you can tell from this image of Cessna 180 trim wheel


Perhaps a simpler approach to the spiral on the trim wheel could be a bolt on a nut or threaded rod that also moves a potentiometer to read the position of the trim wheel.

[fordgt40]

Nat

DC motors can be controlled by Pulse Width Modulation (PWM) using either of the contoller links below


http://cgi.ebay.co.uk/DC-and-Stepper...d=p3286.c0.m14

http://www.opencockpits.com/catalog/...s-c-21_34.html

With the Ebay item which only costs £9 you control the motor by 4 digital inputs to the card - motor enable (the card will drive 2 motors) turn left and turn right. The speed is controlled by sending pulses to turn on the motor, then a delay, then off, then a delay and on again. The easiest way to do this is via software and timing loops - an alternative would be to use a 555 timer though this is getting complicated.

I have tried both these cards using SIOC with the USB OC card or with the Ebay one being controlled by three digital outputs from an OC mastercard. By experimenting with timings I can control the speed. Although I have not written the software yet, it is possible by using feedback from potentiometers to drive the throttle levers under autopilot or to give positional feedback from manual intervention.

For trim wheel applications, by using a multiturn potentiometer, it is possible to compare where the trim wheel is, where it needs to go to, calculate distance to go and reduce the speed as you approach the target position. Links to multiturn pots and a SIOC example are below

http://www.rapidonline.com/Electroni...iometers/29588


http://www.opencockpits.com/modules....c=4085&forum=8

There are a number of other control examples in the OC site in the Forum under SIOC examples.

The only drawback to the contoller cards shown is the amount of current they can pass, however, I have no doubt that alternative beefier ones exist.

Regards

David

[Melnato]

Thanks David!

Currently with phidgets DC motor card and Alans FS2Phidgets,
I can control the direction and speed of the motors.

The bit I cant do or get, is where/how to write the positional software code.
Is it within FS2Phidgets or external code?...just cant get my head around it

Nat

[fordgt40]

Hi Nat

Sorry but I have no knowledge of Phidgets and it`s associated software. In the Opencockpits programming language SIOC you can assign a variable to an analoge input from a potentiometer with a range of values that are determined by the sweeper position within the pot - ie 0 is fully closed 512 is mid way and 1024 is fully extended. Therefore, you physically set up the travel on your throttle/pot movement so that when fully open it is 1024 and fully closed is 0. If you want to move the throttles to mid position ie 512 then you go into a loop of sending a move motor command and read the pot value until you get a value of 512.

I do not know the commands within F2Phidgets, but the above is the basic logic E&OE

Hope this helps

Regards

David

[Melnato]

Thanks David!

Thats the theory...Ill have to give it a crack.

Do you have to use OC cards with SIOC or can i use phidgets cards? sorry...

Nat

[CocnutAir]

Nat,

Short answer. yes.
I am planning on posting documentation on the newer fs2phidget version.
Send me an email and I will send you a pdf overview.

Regards,
Alan.