Clément: Created page with "= Motorshield use it page = add links to get back add a descriptive header... == Things you should know == Remember, YMMV: this is a prototype, not a commercial product. * PWM..."

2011-12-13T22:53:59Z

Created page with "= Motorshield use it page = add links to get back add a descriptive header... == Things you should know == Remember, YMMV: this is a prototype, not a commercial product. * PWM..."

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= Motorshield use it page =
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add a descriptive header...

== Things you should know ==
Remember, YMMV: this is a prototype, not a commercial product.
* PWM frequency shall be under 11 kHz according to datasheet. It can be selected when you create a ''AF_DCMotor'' object: "AF_DCMotor motor_1_or_2(1,MOTOR12_2KHZ);" or "AF_DCMotor motor_3_or_4(3,MOTOR34_2KHZ);"
* I think I ended up messing with signals, that is motor x forward/backward isn't 100% garanteed to be the same as for Adafruit's version. That's lame, but it seems okay to me, given that it is a prototype. One can still pilot all four DC motors, you just have to figure out which one is where and goes which way - or wait for the final HW revision, or the specific SW library.
* because of previous issue, stepper support most probably won't work out of the box.
* speed value is messed up, see below.
* you can read each H-bridge status flags (see datasheet: indicates if everything's fine), if you have the right 0 ohm resistor soldered.

== Setting speed for DC motors ==
The PWMing for speed is an active low on the MC33932 vs an active high on the L293D. I have been lazy to implement a HW thing to compensate for that. I suppose I'll have to decide what I end up doing: either keep the hw simple or respect full pin/sw compatibility.
Anyway, on this prototype, speed values are inversed ! that means, "motorX.setSpeed(255);" will stop the motor and "motorX.setSpeed(0);" will have it go fullspeed.

== Current feedback feature ==
To use the current feedback feature, you should:
* have the right 0 ohm (eg, bridge) resistors in place (check schematic)
* do something like "analogRead(MOTORX_FBPIN)" with "const int M1_FB = A0;//M1 current feedback","const int M2_FB = A1;//M2 current feedback","const int M3_FB = A3;//M3 current feedback","const int M4_FB = A4; //M4 current feedback".
* use the datasheet, schematic and your brain to find the value ! Or read below.

How to find the right code to have a meaningful value:
*The current mirror on feedback pin is 0.24% of load current.
*The resistor in place has a value of 270 ohm (standard precision).
*Therefore, a 5A current will achieve 5*0.0024*270 = 3.24 volts seen on the ADC
*The ADC is 10bits with a 5v reference, so this 5A current will result in 3.24/5*1024 = 664 approx.
*Then 5/664 (or 0.00753) is the factor to have a value in amps.
*An almost correct code might be something like "value_miliamps = 8*analogRead(MOTORX_FBPIN);". Remember that the Arduino doesn't like floating point variables nor making divisions (no dedicated hw) and there are imprecisions here and there, so a x8 factor should be good enough.
*Note that at 6.5A the overcurrent protection kicks in, so the ADC should be fine in any case.

== Code example ==
formating sucks, sorry !
<nowiki>
// Adafruit Motor shield library
// copyright Adafruit Industries LLC, 2009
// this code is public domain, enjoy!
// adapted for Electrolab Motorshield prototype

#include <AFMotor.h>
const int STATUS_FLAG_1 = A2;//H-bridge1 status flag
const int STATUS_FLAG_2 = A5;//H-bridge2 status flag
const int M1_FB = A0; //M1 current feedback
const int M2_FB = A1; //M2 current feedback
const int M3_FB = A3; //M3 current feedback
const int M4_FB = A4; //M4 current feedback

//we need PWM freq < 11kHz
AF_DCMotor motor1(1,MOTOR12_8KHZ);
AF_DCMotor motor2(2,MOTOR12_8KHZ);
AF_DCMotor motor3(3,MOTOR34_8KHZ);
AF_DCMotor motor4(4,MOTOR34_8KHZ);

void setup() {
Serial.begin(9600);
Serial.println("Motor test! Everyone full forward !");

//enable status flag reading
pinMode(STATUS_FLAG_1, INPUT);//Status flag1
pinMode(STATUS_FLAG_2, INPUT);//Status flag2

// turn off (!!) all motors
motor1.setSpeed(255);
motor2.setSpeed(255);
motor3.setSpeed(255);
motor4.setSpeed(255);
motor1.run(RELEASE);
motor2.run(RELEASE);
motor3.run(RELEASE);
motor4.run(RELEASE);

// turn on (!!) all motors
motor1.setSpeed(0);
motor2.setSpeed(0);
motor3.setSpeed(0);
motor4.setSpeed(0);
motor1.run(FORWARD);
motor2.run(FORWARD);
motor3.run(FORWARD);
motor4.run(FORWARD);
}

void loop() {
int tempval;

Serial.print("motor1 current(mA):");
tempval = 3*analogRead(M1_FB);//check the datasheet & schematic, value in mA
Serial.println(tempval);

Serial.print("motor2 current(mA):");
tempval = 3*analogRead(M2_FB);//check the datasheet & schematic, value in mA
Serial.println(tempval);

Serial.print("motor3 current(mA):");
tempval = 3*analogRead(M3_FB);//check the datasheet & schematic, value in mA
Serial.println(tempval);

Serial.print("motor4 current(mA):");
tempval = 3*analogRead(M4_FB);//check the datasheet & schematic, value in mA
Serial.println(tempval);

Serial.print("status flag1:");
if(HIGH==digitalRead(STATUS_FLAG_1))
Serial.println("ok");
else
Serial.println("nok");

Serial.print("status flag2:");
if(HIGH==digitalRead(STATUS_FLAG_2))
Serial.println("ok");
else
Serial.println("nok");

Serial.println("");
delay(1000);
}
</nowiki>

Projets:Perso:2011:Motorshield:use - Revision history

Clément: Created page with "= Motorshield use it page = add links to get back add a descriptive header... == Things you should know == Remember, YMMV: this is a prototype, not a commercial product. * PWM..."