SVP-324 motor control

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1

Hello everybody!
I need help to control motors in SVP-324. I wrote an extremely simple program

#include <pololu/orangutan.h>
int main() {
   int M1_PWM = 50;
   set_m1_speed(M1_PWM);
   clear(); // just to remove garbage from display
   while(1) { ; }
}

I cannot say it does not work, but it does not work as I expect. The program sets the speed of Motor 1 to low value (+255 is the maximum). The motor starts to spin, but non-uniformly. With period of about 2 seconds it speeds up and slows down. Speed variations are of about 80% at this speed value (M1_PWM = 50). When I increase it, the speed increases and relative variations become smaller, but still clearly noticeable. Another motor behaves exactly in the same way.

I worked wit DC motor control in my previous projects with PICs. Even without PID control motor speed was pretty constant. At least variations were unnoticeable without precise measurements. What do I do wrong? I am lost is three commands!

Just in case I provide some information about my circuit. Recently I updated SVP-324 firmware to version 1.01, because I was planning to run PID control and I have quadrature sensors on each motor. Probably, the version of the Firmware does not matter at this time, because the auxiliary PIC does not control H-bridges. I did not run this code before updating the Firmware. I have motors from Pololu (2 x #1101 100:1 Micro Metal Gearmotor HP) with encoder set (1 x #1218 Pololu 42x19mm Wheel and Encoder Set). I power my controller from 6V 1200mA adaptor. I tried to power it from 7.5V 2500 mA adaptor just to see if I have enough power. Motors behavior does not change.

Can anybody help?

Thank you.

Konstantin

2

Hello, Konstantin.

The behavior you describe for your motor is definitely not good.

Are you sure that your tire is not hitting something as it turns? While I was testing your code using my SVP-324 and an encoder set, my tire was hitting my chassis and it caused a problem similar to what you describe.

If that doesn’t solve your problem, then make sure you are using the right version of the Pololu AVR Library: the link step should have this command-line option: -lpololu_atmega324p.

Also, I’d like to know what your motor indicator LEDs are doing. When you set the speed to 50, the motor 1 green forward indicator LED should light dimly but steadily.

-David

3

Hello, David!
You were right. It was pure mechanical problem. The rim of the wheel periodically touched the base. Now everything works fine.

Thank you.

Konstantin