motor hat parallel use of channels

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robotxy
 
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motor hat parallel use of channels

Post by robotxy »

I have a dc motor of 2A operating current. Since the MotorHAT has a limit of 1.2A per channel, can I use two channels parallel to drive one motor ? For example, can I use M1 and M2 wiring connections in parallel to run one motor to get the higher current capacity needed ?
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adafruit_support_bill
 
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Re: motor hat parallel use of channels

Post by adafruit_support_bill »

Unfortunately, no, for a couple of reasons:

1. It is not possible to change the output state of two channels as a single atomic operation. This leaves open the potential of one bridge output being in opposition to another wired in parallel - leading to a dead short to ground. A possible workaround is to be extra careful in your coding to make sure both bridges are turned off before actually reversing direction. But...

2. The PCA9685 PWM outputs are staggered, so unless you were always running at full throttle (100% duty cycle) the PWM pulses would not be in sync and the outputs would be fighting each other.

The DRV8871 would be a better way to go. It can handle a 2A motor: https://www.adafruit.com/product/3190

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robotxy
 
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Re: motor hat parallel use of channels

Post by robotxy »

Thanks for the reply. Understand now why I can't use two parallel MotorHAT outputs going into one motor. So I will go with DRV8871 which can provide 2A operating current that I am looking for.

However I have four dc motors to control. Can I still use the I2C controlled PCA9685 in the motorhat and tap the four PWMs and feed them into four DRV8871 s ? How do I access the four PWM signals coming from PCA9685 of the motorhat ?
Thanks.

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adafruit_support_bill
 
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Re: motor hat parallel use of channels

Post by adafruit_support_bill »

Can I still use the I2C controlled PCA9685 in the motorhat and tap the four PWMs and feed them into four DRV8871 s ?
To have both speed and direction control, you really need 2 PWM channels per DRV8871. There are 4 spare PWM channels available on the HAT. They are in the box labeled "xtra pwm" in the center of the board. You can access them using the PWM Servo library.

Image

The other option would be to use the PWM Servo HAT or PWM Servo Breakout boards. These have all 16 of the PCA9685 PWM channels accessible.

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