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Thread: Sensing RC receiver impulses & PWM motor control
www.piclist.com/techref/io/motors.htm?key=motor
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face BY : Valehrach Roman email (remove spam text)



Hi to all PICers out there!

In an attempt to reduce the amount of 'reinfented wheels' (esp. my own's)
I'm looking for some code (preferable with application notes for the circuits)
concering radio control and motor control - preferable with PICs (but no
exlusive):

1. Decoding the servo impulse/s from a RC receiver:
  * preferable a 'self learning' application
  * determination of multiple levels of modulation (centre, and max. would
    certainly be of help for the beginning)
  * 'fail save'-state whilste there is a signal loss/no signal

2. Controlling of a model motor (car/aeroplane):
  * multiple steps of speed/fine control of revolutions
    preferably PWM (pulse width modulation) with a high frequenzy
  * acceleration/deceleration slope (programable)
  * high currents of 50A (standard, with shorttime current of up to 100A)
  * single/dual direction control
  * motorbrake
  * current sensing to detect shorts/blocking motor

I thing it's obvious that I'm trying to build a RC motor controller. Since I
know that many commercial products nowadays have a PIC (I know of 54 or 84)
inside, it should be possible to build such a thing.
my draft for such a device:
  combination of the above (1., 2.)
  PIC 16C84 (still the only one I can program) with information storage
  in internal EEPROM (receiver impuls, slew rate, motor data)
  modular final stage for cars or planes (brake, single/dual direction,
  etc.)

Since there are so many (aren't there?) RC modellers on the list it would be
interesting to share informations/experiences on the subject of using PICs in
RC models (in the whole and motor controllers especially).

With the minimal research I have done so far I also encountered some questions:
* What is the best way to do multiple tasks with a PIC (esp. 16C84)?
 Ex.: In a motor controller I would have to watch for the incomming impulses
      whilst pulse width modulating a motor, sensing the current, etc.
      To bad if I'm stuck in a wait loop... (If you know what I mean :-)
      Since I want to use the 84 - How do I put the interrupts to best use?
* Which (power) transistors should I use in the final stage?
  BUZ11 looks promissing.. but SIPMOS TEMPFETs/PROFETs/TOPFETs also look good
  (though a much higher price, but temperature/shorts protection)
  What would be the "best" transistor for my task ? (low Rds[on] <50mOhm,
  Id[max] >20A, reasonable pricing/pice, etc.)

  BTW: I bought some BUZ11 which have an 'A' mark on the cooling metal.
       Does that mean that those FETs are in fact BUZ11As and not BUZ11s.
       The plastic housing has printed 'BUZ11' on it (NO A) but what about
       the mark on the metal... ???
       What's the best way to measure the Rds[on] with hobbiest equipment
       (some DVMs [not acurate in mOhms-Measuring], Scope [10MHz])?


Finaly you might ask yourself, why I don't buy one of those commercial juwels
(Ahh.. controllers)?
A. Inflexibility: ('Please define [in-]flex-i-bil-i-ty... Ahh')
  Commercial controllers are trimmed for a single task. If I want to
  control a model car and a model aeroplane I would have to buy two
  controllers <cliiing>, although I wouldn't use both models at the same time.
  It's allmost impossible to find a controller which is really adequat for the
  given task. 'Testing a controller ? - Impossible - buy it first!' <cling>
  I also want to control the slew rate ('Expensive... 8-]' <cling,cling>) of
  the motor with my PC ('Impossible... :-(').

B. The Price: (Isn't it allways ?)
  As I wrote above - RC motor controllers are sold at the price of juwels.
  But a diamond wouldn't explode/burn out if you connect the power supply
the     wrong way - And who didn't/doesn't make mistakes. Such controllers also
  age at a rapid speed (Every year there is something new). If the nowadays
controller is damaged nobody but the manufactorer will repair it (time delay,
  prohibitive cost). So it's off to the bank to get a new loan.

C. Experience:
  I'm still very new to the PICs. I know it will be a hard way to a functinal
  unit but I certainly will learn my share.
  With the knowledge gained I could easily repair the RC motor controller :-)
  Thus *no more garbage collection* for high tech stuff! ;-)
  And ... 'What you know You KNOW.'

Thanks in advance for your response(s)!

****************************************************************************
*   Roman VALEHRACH               eMail-to: .....e8927070spam@spam@student.tuwien.ac.at  *
*   student of technical university vienna     (subject of annual change)  *
*                                                                          *
*  "SHARE AND ENJOY, SHARE AND ENJOY... "               furry creatures  ->*
*  "The EARTH: ..... (ed., revised: MOSTLY) HARMLESS"   from alpha-centaur *
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Subject (change) Sensing RC receiver impulses & PWM motor control

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