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Silverback01
Joined: 30 Sep 2008 Posts: 11
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Firgelli Linear Actuators |
Posted: Mon Jun 28, 2010 10:23 am |
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I'm working with some Firgelli linear actuators http://www.firgelli.com/products.php and they are potentiometer-controlled. Is there a way to control something like this through a microcontroller? It would be a serious waste of weight (for an airplane) to have to use a servo to control a pot, which controls the linear actuator.
Thanks! _________________ John |
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PCM programmer
Joined: 06 Sep 2003 Posts: 21708
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Posted: Mon Jun 28, 2010 12:19 pm |
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You need to post the part number of the actuator that you're using.
This one, for example, has a built-in microcontroller, and has the option
to use 4 different interfaces. One of those is the standard RC servo
interface. You don't need potentiometers to control it. A PIC can do it.
http://www.firgelli.com/pdf/L12_datasheet.pdf
CCS has some driver code to generate the servo signals:
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c:\program files\picc\drivers\servos.c
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Silverback01
Joined: 30 Sep 2008 Posts: 11
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Posted: Mon Jun 28, 2010 12:35 pm |
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The model is the PQ12. The ones that were ordered were the potentiometer-controlled ones which were used for a demo. I am trying to find out if they can be implemented in the robot in order to save a little money, but I may have to reorder them with the RC servo interface. _________________ John |
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Ttelmah
Joined: 11 Mar 2010 Posts: 19481
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Posted: Mon Jun 28, 2010 1:55 pm |
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As far as I can see, there is no such thing as a potentiometer controlled version!.
The 'P' says it has a potentiometer _output_. However the input, seems to 'auto switch' between four different interface standards, and will automatically detect a RC servo input, or 0-5v. Either could be driven very easily by a PIC. If you choose a PIC with a PWM output, and add a reasonable integrator to the output of this, you can use this as a 0-5v source in place of the potentiometer. Then to get real accuracy, use the output from the potentiometer built into the unit, and adjust the PWM to give the required position.
Best Wishes |
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Ttelmah
Joined: 11 Mar 2010 Posts: 19481
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Posted: Mon Jun 28, 2010 2:22 pm |
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Sorry, I was reading the data sheet in PCM programmer's reply.
However if these are positionable using a pot, then the answer stands. They must have a controller fitted.
You need to find out the letter/number sequence after the PQ-12 part. This is a bit like saying "it's a Ford [spam]". It is the letters and numbers afterwards, that say the trim level, engine, gearbox etc. etc.. These are what matter in terms of control.
_All_ can be controlled by a PIC. The most complex would be a 'bare' unit, requiring H-Bridge control (much easier on a PIC with a more sophisticated PWM unit). The simplest one with a controller already present.
Best Wishes |
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Silverback01
Joined: 30 Sep 2008 Posts: 11
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Posted: Mon Jun 28, 2010 4:38 pm |
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I've been emailing the company today and still haven't made much progress. The datasheet I was sent for the PQ-12-20-30-A http://www.firgelli.com/pdf/PQ12_datasheet.pdf shows a five-wire ribbon cable--three of which are tied to a potentiometer, and two for power. They have a control board (CIB) http://www.firgelli.com/pdf/CIB_datasheet.pdf that can apparently take an input from a standard R/C receiver and do a bunch of hocus-pocus on it to get the actuator to move where the user wants it to. I have their control board and there are a lot of components on it in order to make it robust. (Note the sliding potentiometer on the right of the CIB.)
However, since my application is for a very small UAV, the board eats power and subtracts usable payload weight and volume. Firgelli does have a larger version of this actuator (but heavier), which is the L-12 and has an option to plug directly into a receiver. I may have to make the sacrifices in weight, and cost to save volume and headache and go with the bigger one.
In a nutshell, the five wires on the PQ-12's engineering drawing is the problem area.
Thanks again. _________________ John |
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Humberto
Joined: 08 Sep 2003 Posts: 1215 Location: Buenos Aires, La Reina del Plata
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Posted: Mon Jun 28, 2010 5:19 pm |
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Quote: |
It would be a serious waste of weight (for an airplane) to have to use a servo to control a pot,
which controls the linear actuator.
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I guess that you didnĀ“t catched the point. The servo is used to control an electro mechanical actuator not a pot.
The potentiometer function is only to give the feedback position (error)info needed in a closed loop control algorithm.
Regarding the servo controller, after power up the CIB controller scan some pins of the X6 connector
to know which of the four controlling mode was selected ( in my opinion there are a mistake in the pins
description, is should be: 1, 2, 3 insted of 2, 3, 4 as stated in the CIB pdf info page 1).
After receive a valid signal, the CIB will self-configure to the corresponding interface controlling
mode (0-5V, 4-20mA, RC servo PWM).
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In a nutshell, the five wires on the PQ-12's engineering drawing is the problem area
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It is very straightforward, these five wires should be connected to the X2 in the CIB board.
To use the control actuator potentiometer do not forget to change J1 accordingly to EXT position.
Be carefull because there are some inconsistency in the names used in the technical info.
Humberto |
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