Debugging DualTB9051FTG Motor Shield

jfrye11 · December 20, 2021, 3:04pm

I have been playing with the DualTB9051FTG motor shield. I have been driving it with this battery, Pololu - Rechargeable NiMH Battery Pack: 7.2 V, 2200 mAh, 3x2 AA Cells, JR Connector . I am using a pair of these motors Pololu - 4.4:1 Metal Gearmotor 25Dx63L mm HP 6V with 48 CPR Encoder

Things have been going smoothly for the most part. My interface to powering the motors has been this function from the library (this is for the first motor)

github.com

pololu/dual-tb9051ftg-motor-shield/blob/d99a3380dd5ed98cb25541ffbd671e53843b5fef/DualTB9051FTGMotorShield.cpp#L89

    
      
              // PWM frequency calculation
              // 16MHz / 1 (prescaler) / 2 (phase-correct) / 400 (top) = 20kHz
              TCCR1A = 0b10100000;
              TCCR1B = 0b00010001;
              ICR1 = 400;
            }
          #endif
          }
          
          
// Set speed for motor 1, speed is a number between -400 and 400
          void DualTB9051FTGMotorShield::setM1Speed(int speed)
          {
            unsigned char forward = 1;
          
          
  if (speed < 0)
            {
              speed = -speed;  // Make speed a positive quantity
              forward = 0;  // Preserve the direction
            }
            if (speed > 400)  // Max PWM dutycycle
              speed = 400;

I have gotten to a point in my poking around where I can no longer drive the motors, even if I provide power of 400.

I am wondering if I may have either done something to damage the shield or if simply my battery needs recharging. Using my multi-meter, I did a reading on the 7.2V battery, which read ~6.4/6.5V.

Can anyone confirm this means the battery requires recharging to adequately power the motors via the shield?

BrandonM · December 20, 2021, 8:27pm

Hello.

Yes, 6.4-6.5V is severely discharged for a 7.2V NiMH battery pack, so the first thing you should try doing is charging the batteries. When fully charged, each cell should be around 1.4V, so the fully-charged voltage of that battery pack should be closer to 8.4V at that point. It is generally a good idea to charge it when the voltage drops below 1.1V per cell (6.6V for that pack).

If that does not fix the problem, you can post pictures of your setup that show all of your connections, as well as the code you are currently using, and I would be happy to take a look.

Brandon

jfrye11 · December 20, 2021, 9:41pm

I appreciate the timely response. I have gone ahead and purchased one of these Pololu - iMAX B6AC V2 Balance Charger and Discharger . Is this the preferred solution you offer for recharging?

BrandonM · December 20, 2021, 10:16pm

The iMAX 6BAC V2 is a well made charger that works with various kinds (e.g. different battery chemistries, nominal voltages, etc.) of battery packs, including the 7.2V NiMH pack you are using.

However, please note that it is has a lot of more complex features and abilities that are not necessary if you are just planning on using it with NiMH batteries. So, if that is the case, you can probably find a simpler charger, although I do not have any specific suggestions for one.

Brandon