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creating boards to control model airplane — Parallax Forums

creating boards to control model airplane

ashleygashleyg Posts: 1
edited 2007-07-16 20:44 in Robotics
We are trying to make the control surfaces of a model airplane controlled by a programmed board for a wind tunnel test we are planning. However we're not sure how to approach this, meaning what board/s we might need. We will need to command 8 servos to determined angles for the ailerons and other surfaces. Power might be an issue so we would like something that can easily have additional power supplied. Any help would be appreciated. Thanks

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2007-07-16 20:10
    The BS2 with a Board Of Education (BOE) would be perfect for this. I believe a servo takes about 100 mA when moving, so a single 6-volt DC 1 amp supply would work fine.

    A model airplane servo is commanded from the BS2 with a 'PULSOUT' command, repeated every 20 to 50 mSec. The 'PULSOUT' duration is 1 mSec to 2 mSec, with 1.5 mSec being 'centered'. Thus 8 servo's would take 16 mSec 'worst case', allowing you 4 to 34 mSec for processing before you'd have to 'refresh' all 8 servo's again. This is very practical.

    Plus, the BOE/BS2 serial port would allow you to communicate with an attached PC for control on-the-fly, if desired.
  • Capt. QuirkCapt. Quirk Posts: 872
    edited 2007-07-16 20:44
    {(edit) This is a subject that I have experience in, but with flying models. My friends and I race giant scale pylon racers (USRA) and much of the what I have to say is based on what won't work in a flying model and why it won't work. Perhaps you can use a 1 stamp to read data from your sensors and another·stamp to control your servos to complete your·initial testing with. After you have a test program finished perhaps you could use a LED to signal the next predetermined test and eliminate the sensors that require pause statements or just reprogram the stamp each time. Otherwise perhaps this post is a better example of why a Propeller is necessary, especially if you want to implement·your system in a flying model in the future.}



    First off your going to need a servo controller and a BS2, SX, or Propeller to control it. If you use a Stamp, you need a Parallax Servo Controller. It may also work with the SX, but I haven't tried that yet. The SX can only transmit serial data 1 byte at a time, where as the BS2 series can transmit a word +.

    Don't let the processor data specs fool you, there are processors like the SX and Propeller that·have more horsepower,·but the Pbasic language trumps them by making it easy to finish a project in the least amount of time. **·(If you do have time to learn a new language, the Propeller's ability to perform "Parallel" processing vrs any other processor's "Serial" processing is also a huge advantage)**.

    When you use the servo controller, you can't have any significant PAUSE statements in a BS2 or SX program that controls it. But with a Propeller·you can assign the device or routine that requires the pause to another Cog.

    There are Servo Controller options besides the Parallax Servo Controller. In the SX Forums under the sticky "Best SX Threads" there are several links to servo controllers including a link to the·May, 2007 Nuts n Volts article #143 that you can adapt·to be controlled by another processor.

    Second, you will need to keep track of your·control surfaces and possibly the angle of the fuselage. There are 2 accelerometers available from Parallax that can be used report the·angle of a control surface or fuselage·to the processor. But both of them have a PAUSE 200ms or greater statement·in each of the sample programs.

    Those "PAUSE" statements will disable your servo controller. I own 2 of the Mesmic 2125's but I haven't used·either yet and so I have no experience·with either the, Mesmic 2 axis·or Hitachi·3 axis. Maybe someone else can tell you if the "Pause" statements are necessary or not.

    Another way to watch your control surfaces would be with a 10K pot and an 8 bit ADC like the ADC0834 0r ADC0838. Either have plenty of resolution to report angles without a pause statement.

    Serial LCD's can add significant pauses to a program to, I prefer the parallel style for that reason.

    Bill

    ·
    Allenlane 5 ,
    (makes a good point about computer control, the Parallax USB Servo Controller can be completly controlled by a PC and has an excellent interface program to accomplish it)
    Post Edited (Capt. Quirk) : 7/16/2007 8:55:14 PM GMT
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