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
http://www.azcessna.com/images/trimwheel.jpg

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-Motor-Driver-Board_W0QQitemZ310109464328QQcmdZViewItemQQptZUK_BOI_Electrical_Test_Measurement_Equipment_ET?hash=item4833f6e708&_trksid=p3286.c0.m14

http://www.opencockpits.com/catalog/electronic-cards-iocards-motors-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/Electronic-Components/Resistors-Potentiometer/Control-Potentiometers/3W-Multiturn-potentiometers/29588


http://www.opencockpits.com/modules.php?op=modload&name=Forums&file=viewtopic&topic=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 :D

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.

[OmniAtlas]

This thread is 7 years old but still pertinent today.

Cheers - I am still trying to decide if I should use a phidget or OC DF motorcard for my trim wheel. I would be open to suggestions, thanks.

[brianwilliamson]

2 ways you can get the position of the Trimwheel.
One ito use an ordinary pot and gear it as in this pic:



Or connect a multi turn pot direct or geared. (10 turns I think)

The 12 volt motors that are geared down to very low rpm are strong enough to break your arm !! So you do not need a 10hp. motor.


I use an ordinary pot and geared as in in the pic. using IO DC Motor card, which handles it without any hassle at all.

Not sure if this will help as I guess it depends on the room you have to install all this.


............Brian W.

[OmniAtlas]

Hi Brian, I must have been confused because I did not know the pot had to have a physical connection to the trim wheel. I was under the impression the motor card does some voodoo magic with the pot and is able to position sense.

I checked on the throttle shaft and it seems it turns 6 times from negative to positive trim.

Do you need the OC motor plus card or will the regular version do?

Unfortunately I do not have the expertise to build a pot into a trim wheel.

[brianwilliamson]

Ok a quick setup of how it works:

The trim wheel as you have indicated does 6 revolutions from full forward to full aft. The sofware and the DCMotor card need to know where the trim wheel is exactly.


So you connect a potentiometer to the trim wheel physically and connect the 3 wires from the pot., to the card.



The card then tells the DCMotor board to move the trim wheel with the 12volt motor to wherever the potentiometer needs to be.

The software does all the work, as it reads the pot.... and if it does not match where the aircraft says the trim should be, it then turns the motor in that direction.

As I said it depends how you can connect the Pot., but there should be one already connected to the trim wheel, as the real aircraft works in exactly the same way.


Hope I explained that a bit better. I am about to pull my throttle and trim out as I only have 4 turns on my setup, so need to rebuild.


Cheers................Brian

PS......Ordinary one is ok, but later one maybe more reliable

[OmniAtlas]

Hi Brian,

I've checked my pedestal and I don't think there are any connections from the trim wheel to the pots in the unit -- in the TCU (throttle control unit), where the pots sit, only the levers are connected. I will keep on experimenting, otherwise I will try and imagine how I can construct a mechanism to house the pot and dc motor.

I would like to connect the DC motor directly to the shaft seen here --

http://www.mycockpit.org/forums/attachment.php?attachmentid=11649&stc=1

[brianwilliamson]

I should perhaps have added that you may connect the pot., to either the trim wheel or the trim indicator.

Both do the same job except the indicator does only turn a fraction of a revolution whereas the trim wheel does 6 revolutions.



Cheers.................Brian W.