5V Power

[rbtying]

I've been having some issues with powering my robot's microcontrollers recently.  Currently the setup is as such:

11.1V LiPo -> Motor Vin & GND
7.4V LiPo -> Arduino Mega barrel jack (Vin/GND)
Arduino Vcc -> ATMega328 Vcc -> SN745510 Vcc1
Arduino GND -> ATMega328 GND -> SN745510 GND

The problem is that the motors will start spinning, then suddenly stop after about 3-5 seconds.  Since the entire system works as expected when an external +5v is applied (from voltage supply and from USB programmer), I think the problem's with the regulator; however, it doesn't heat up or anything.  Any ideas for a solution?  Thanks in advance.

[Webbot]

What pins are you using on the SN745510? Just wondering if some are left floating which then disable the output

[waltr]

Is the control lines from the processor failing or is the power to the motors failing?

[rbtying]

I'm using all of them (all four half-H-Bridges), something like this:
         _
P09  | | +5v
P08  | | P12
M1A | | M2A
GND | | GND
GND | | GND
M1B | | M2B
P07 | | P11
BAT | | P10

P* are Arduino pins, with 9 and 10 being the EnablePin PWM.

Waltr,
    I have not checked if it's control lines or power to motors, I'll respond back in a few minutes.

---EDIT---
  The control lines are failing, although both enable pins are working properly, the voltage to the input lines is 0v on both. 

[Webbot]

Is it a code problem? Does it stop sending the controls after the same time delay?

[rbtying]

Hm... the time delay is quite variable:

Code: [Select]

#define EN_1 9
#define EN_2 10

#define M1_A 7
#define M1_B 8

#define M2_A 11
#define M2_B 12

void setup() {
  analogWrite(EN_1, 255);
  analogWrite(EN_2, 255);
 
  pinMode(M1_A, OUTPUT);
  pinMode(M1_B, OUTPUT);
 
  digitalWrite(M1_A, HIGH);
  digitalWrite(M1_B, LOW);
 
  pinMode(M2_A, OUTPUT);
  pinMode(M2_B, OUTPUT);
 
  digitalWrite(M2_A, HIGH);
  digitalWrite(M2_B, LOW);
 
  pinMode(13, OUTPUT);
}

void loop() {
  digitalWrite(13, HIGH);
 
  digitalWrite(M1_A, HIGH);
  digitalWrite(M1_B, LOW); 
 
  digitalWrite(M2_A, HIGH);
  digitalWrite(M2_B, LOW);
}
It continuously writes the values out.  I think a lot of you are forgetting the problem doesn't appear when using an external supply, so I think it must be something to do with the regulator?

[madsci1016]

Could be noise. Try adding a .1uF and 10uF capacitor to both the Motor VIN and Arduino VIN.

Try adding a Serial.Println() to your loop function, and watch the output in a terminal. If it stops printing out when the motors stop, your Arduino is resetting and locking out.

[rbtying]

You're right, it was noise.  I put in the capacitors, and everything worked, so I'm happy for now... time to build the rest.