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Topic: Motorshield and electromagnet ? (Read 1 time) previous topic - next topic


Feb 14, 2011, 05:29 pm Last Edit: Feb 14, 2011, 05:31 pm by kuno86 Reason: 1
Hi ,
i have a rc-car with a magnetic steering (+volts right, -volts left) which i'm controling it with a L298P Motorshield.
The only Problem is that the steering kinda vibrates an won't really move.
So my question is, how can i make the motor shield working with this electromagnet ?
Or could PLL-mode on this shield (for three-phase-motors) control it ?
Before i do anything maybe dangerous for the circuits, i want to ask someone with more experience :)


What is the code you're using to control the motorshield?  You don't want to PWM the motor driver for an electromagnet steering mechanism.  Either drive it full on one direction, full on the other direction, or full off.  If you PWM the signal, that will cause the electromagnet to vibrate.


Feb 15, 2011, 12:36 am Last Edit: Feb 15, 2011, 12:21 pm by kuno86 Reason: 1
Thats the code:
Code: [Select]

#include <SPI.h>
#include <Ethernet.h>
#include <Udp.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = { 10, 56, 35, 178 };
byte gateway[] = { 10, 56, 35, 1 };
byte subnet[] = { 255, 255, 255, 0 };

#define MAX_SIZE 32 // maximum packet size
char packetBuffer[UDP_TX_PACKET_MAX_SIZE]; //buffer to hold incoming packet
byte remoteIp[4]; // holds recvieved packet's originating IP
unsigned int remotePort; // holds received packet's originating port

const int ledPin = 13;

int E1 = 5;
int M1 = 4;
int E2 = 6;
int M2 = 7;

void setup() {
 Ethernet.begin(mac, ip , gateway, subnet);
 pinMode(ledPin, OUTPUT);

void loop() {
 int packetSize=Udp.available();  // holds received packet size
 int DriveSpeed = 0;
 boolean SteuerFehler;
   int packetSize = packetSize-8;   // minus 8-Bit Header
   Udp.readPacket(packetBuffer,UDP_TX_PACKET_MAX_SIZE, remoteIp, remotePort);

for (int i=1;i!=8;i++)    //Searches for illegal characters inside the control-string
 if(packetBuffer[i]!='-' |packetBuffer[i]!='x' |packetBuffer[i]!='0' |packetBuffer[i]!='1' |packetBuffer[i]!='2' |packetBuffer[i]!='3' |packetBuffer[i]!='4' |packetBuffer[i]!='5' |packetBuffer[i]!='6' |packetBuffer[i]!='7' |packetBuffer[i]!='8' |packetBuffer[i]!='9')
if (SteuerFehler)
 packetBuffer[0]='-';    //Reset the control-string to all off

   case '0': DriveSpeed=30;break;
   case '1': DriveSpeed=55;break;
   case '2': DriveSpeed=80;break;
   case '3': DriveSpeed=105;break;
   case '4': DriveSpeed=130;break;
   case '5': DriveSpeed=155;break;
   case '6': DriveSpeed=180;break;
   case '7': DriveSpeed=205;break;
   case '8': DriveSpeed=230;break;
   case '9': DriveSpeed=255;break;

if(packetBuffer[0]=='-' & packetBuffer[1]=='-') //Stop
   {digitalWrite(M1,HIGH);analogWrite(E1,DriveSpeed);} //Reverse
if(packetBuffer[1]=='x')                       //
   {digitalWrite(M1,LOW);analogWrite(E1,DriveSpeed);}  //Forward    

if(packetBuffer[2]=='-' & packetBuffer[3]=='-') //Straight ahead
if(packetBuffer[2]=='x')                        //Left
if(packetBuffer[3]=='x')                        //Right                


Steering-part is at the last lines.

I send a control-string of 8 characters, [2] is left and [3] is right, i'm always using the max. 255 for steering in one direction and LOW/HIGH. If [2] or [3] is not 'x', i set it to 0 volt.

It currently uses PWM and i'm not sure what the PLL-mode is...
When i listen to the sound that it makes, i get the feeling that the controller is giving out a stuttering (_-_-) voltage, like on->off->on... in very fast.
Maybe the magnet could work better without that fast on-off...

I have set the Motor2 to PLL, but i don't rellay know a thing about it.
Heres what i have figured out so far:
M2 LOW -> Does nothing on any E2-Value ?
M2 HIGH -> enables Speed Control (in only one direction ?)

With M2=HIGH and E2=0, i can turn left just fine. But what about Right ?


E1 and M1 are the FWD/Backward setting pins, Reverse is HIGH, forward is LOW. 
E2 and M2 are the PWM pins, you should be able to use these as digitalWrite pins and not use pwm at all. This will send Full Left with lets say E2 at HIGH and E1 at LOW. Center is E2 = LOW. Full right would be E1 at HIGH E2 at HIGH
"Human beings, who are almost unique in having the ability to learn from the experience of others, are also remarkable for their apparent di


Back to the PWM-mode, it dosent work perfect, but at least i have left and right...

But there was something else i've noticed, the controller seems to get the signal, but then its sending out a low power (~40%) which then switches to the set power value after ~0,5 seconds delay.
shouldn't it give out the full power instantly ?

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