Was the gyro the wrong choice for this application?

Thomas Fletcher · 2010-05-08 16:09

I think I purchased the wrong thing for what I want to do.

I want to make a camera stabilizer that keeps the platform the camera is on horizontal reducing the effects of roll and pitch.

I thought each axis would be similar to a balancing bot so I got a LISY300 Gyroscope module thinking it gave tilt info only to find it gives rate of turn.

I am not understanding the values it is returning at all. Stationary it gives 505, the number then goes up/down randomly seemingly no matter
which way I turn it. I would think it would go down one direction, up the other?

I am totally confused on what information it is giving me.

Thomas Fletcher · 2010-05-08 16:21

ARGH!!!!! Rereading the product info it says :

the LISY300 Gyroscope Module can detect how many degrees it has turned on its planar axis

How do I get that value?!?!?!?

This is the code I am using that was on the product page, I modified it to print the measurement value to the serial terminal.

CON                                                     ' Propeller Setup
  _CLKMODE = XTAL1 + PLL16X
  _XINFREQ = 5_000_000
 
CON                                                     ' Gyro I/O Pins
  DOUT = 0 
  SCLK = 1
  nCS = 2



VAR                                                     ' Gyro    
  long Center
  long Deg               

OBJ                                                     
  DEBUG  : "Parallax Serial Terminal"  
    

PUB MAIN
    dira[noparse][[/noparse]2..1]~~
    Measure
    Calibrate
    DEBUG.start(250000)
    DEBUG.clear
    repeat
       DEBUG.Position(20,20)  
       DEBUG.str(string("Gyro angle: "))
       DEBUG.clearend
       DEBUG.dec(measure)




 
  Measure
  Calibrate

 

PUB Calibrate | Value, Sigma, Minimum, Maximum, Average

  result~
  Sigma~                                       
  Minimum := Maximum := Measure
  repeat 50
    Sigma += Value := Measure                           ' Sum Voltage Readings
    Minimum <#= Value                                   ' Find Minimum Voltage 
    Maximum #>= Value                                   ' Find Maximum Voltage
  Average := Sigma / 50                                 ' Find Average of Samples
  Center := Average


PUB Measure ' Clock data in for 13 bits.  (First three are zero, next ten are data.)

  result~
  outa[noparse][[/noparse]nCS]~    
  repeat 13
    outa[noparse][[/noparse]SCLK]~
    outa[noparse][[/noparse]SCLK]~~
    result := result << 1 | ina[noparse][[/noparse]DOUT]
  outa[noparse][[/noparse]nCS]~~

Thomas Fletcher · 2010-05-08 16:41

Nevermind. Missed an important part of the code.

Deg := Deg + (Center - Measure) / 2

Thomas Fletcher · 2010-05-08 17:43

Well Smile. That is just incrementing the reading fluctuations. This is really really confusing.

Thomas Fletcher · 2010-05-08 21:16

Well, I am getting there. after some reading I am now concerned with drift but I hope to try it when I get a servo. I am hoping to soak up about 30 degrees in each direction
of roll using a servo to control the platform. This is what I got so far.

'servo.init
    dira[noparse][[/noparse]2..1]~~
    Measure
    Calibrate
    DEBUG.start(250000)
    DEBUG.clear
    repeat
       DEBUG.Position(20,18)  
       DEBUG.str(string("Gyro Center: "))
       DEBUG.clearend
       DEBUG.dec(center)

       DEBUG.Position(20,19)  
       DEBUG.str(string("Gyro measure: "))
       DEBUG.clearend
       av := avermeasure
       if av > 508 or av < 504
          Deg := Deg + (Center - Measure) / 2
       DEBUG.dec(deg)
              
       DEBUG.Position(20,20)  
       DEBUG.str(string("Gyro angle: "))
       DEBUG.clearend
       degree := deg / 39
      if degree > 30
          degree := 30
      if degree < -30
          degree := -30
      DEBUG.dec(degree)

       DEBUG.Position(20,21)  
       DEBUG.str(string("Servo angle: "))
       DEBUG.clearend
      if degree > 0  
          servopos := 110 + (degree * 4)
      else
          servopos := 110 - (||degree * 4)
     DEBUG.dec(servopos)

wjsteele · 2010-05-09 13:03

In order to eliminate the drift, you'll need to integrate it with an external source for correction information. An accelerometer coupled to the gyro through a Kahlman filter will do the trick. There is an object in the obex for just that.

Bill

Was the gyro the wrong choice for this application?

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