I am working on a project in which there are system components listed below as module:
- 8 ultrasonic sensors 12-30 V (Sensor module)
- 3 DC motors (Drive module)
- 35 V to 5 V buck converter and a 35 V - 5 V isolated DC-DC converter (Power module)
- 1 Microcontroller (Controller module)
- 2 Encoder (Encoder module)
Let me explain the required functioning of the module. I am using a LiFePo4 battery (26.5 V, 18 Ah) for powering the PCB and I have isolated the sensor module and drive module using optocouplers for the safety of my microcontroller.
The motor module optocoupler uses 5 V logic and the sensor module optocoupler uses 3.3 V, so the sensors gives signals to the controller through an optocoupler and then the controller gives a signal to the motor driver through an optocoupler and the motor runs accordingly.
I am using a buck converter circuit to convert incoming power from the battery to 5 V that it can deliver to the motor side optocouplers and I am using another isolated DC/DC converter circuit to convert the battery voltage to isolated 5 V to power up the microcontroller.
My microcontroller can source 3.3 V to the sensor optocoupler circuit and direct power from the battery is going to the power sensors and the motor driver; there is no regulation or any other circuitry.
Let me attach details of components:
- Buck converter IC 35 V - 5 V MC34063
- Isolated DC-DC converter Hi-link 18~36 V to 5 V
- Microcontroller CC1350 Launchpad
- 2 low power Motor driver DRV8872
- 1 High power motor driver Cytron MD10C
I don't have datasheets of the sensors, motors, and encoder right now but I remember some current ratings:
- Each sensor's current output is 100-200 mA; operating volatge is 12-30 V
- High power motor continuous current which I have noticed is 2-3 A but at some places when it require more torque it reaches 4-4.5 A and the operating voltage is 20-30 V
- Low power motor of which are are two each normally take 500 mA; at some places when they require more torque current reaches to 900 mA and the operating voltage is 20-30 V
My question: when I test the whole system on the bench, and there is almost no torque compared to normal operation, when I then try to put torque on the high power motor, why do both low power motors start behaving abnormally?
They start running with a jerky motion. I have placed a LED on the input from the controller to the driver, that LED also flickers so it seems the motor driver gets a similar signal from the controller I put torque on the high power motor. I want to know why it is happening even though the circuit is isolated (24 V <> 5 V).
Let me share the circuit diagram: