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3.a. Power and Motor Connections

The qik motor controller takes two power inputs: motor power supplied via the VMOT and GND pins at the bottom of the board and logic power supplied via the VCC and GND pins at the top of the board.

Motors and Motor Power

The qik can independently drive up to two bidirectional brushed DC motors, referred to as M0 and M1. The two terminals of each motor should be connected to the qik as shown above. Variable speed is achieved with 7-bit or 8-bit pulse width modulated (PWM) outputs at a frequency of 31.5 kHz, 15.7 kHz, 7.8 kHz, or 3.8 kHz. The highest achievable frequency of 31.5 kHz is ultrasonic, which can result in quieter motor control. Lower frequencies might make the motors louder, but they can decrease power losses due to switching and affect the relationship between PWM duty cycle and motor RPM. The resolution and frequency can be set via the qik’s PWM configuration parameter (see Section 5.c).

The motor direction convention used in this document is that “forward” corresponds to grounding the - pin while PWMing the + pin between VMOT and ground. “Reverse” is the same as forward but with the outputs flipped: + is held at ground while - is PWMed between VMOT and ground. As a result, the motor is rapidly alternating between drive and brake when the direction is “forward” or “reverse”. Variable speed control is achieved by varying the fraction of the cycle that the motor outputs are driving. Full speed arises when the motor outputs are driving 100% of the time (one motor output is held at VMOT and the other at ground), and full braking arises when the motor outputs are driving 0% of the time (both outputs are held at ground). See Section 5.e for more information on the motor commands.

In addition to forward and reverse, the qik 2s9v1 can set its motors to “coast” (i.e. the motor shafts will rotate freely) mode by configuring the motor driver outputs as high-impedance. See Section 5.d for more information.

The motor voltage must be between 4.5 and 13.5 V, and your motor power source must be capable of supplying the current your motors will draw. The qik 2s9v1 motor controller uses the TB6612FNG dual motor driver, which is capable of supplying a continuous 1 A per motor channel, with a peak output of 3 A per channel. Continuous performance is a function of how well you can keep the motor driver cool; addition of a heat sink or increased air flow over the board can allow the driver to output higher currents without overheating. The driver has thermal protection that causes it to shut down when it detects that it is overheating, but it is not a good idea to rely upon this thermal protection to prevent damage to the unit that can be caused by using it out of spec.

Logic Power

The logic voltage must be between 2.7 and 5.5 V and must be capable of supplying more than 15 mA (the logic draws less current at lower voltages and when the LEDs are off). Voltages that fall below 2.7 V trigger a brown-out and cause the device to reset. Note that the voltage on the qik’s serial input must not exceed Vcc.

While it is possible to use the same power source for both your motors and logic, we do not recommend this. Motors typically add noise to the motor power rail, and this noise can negatively impact the functioning of the device if it is introduced to the logic power rail. If you want to use the same power source for both motors and logic, you should decouple the two by using large capacitors and/or a regulator. Even if you use separate power supplies for your motors and logic, you should take whatever steps you can to limit electrical noise from your motors. For example, solder 0.1 uF capacitors across your motor terminals (as shown in the diagram above); using three capacitors per motor (one across the terminals and one from each terminal to the motor can) results in maximum noise suppression. You can further decrease motor noise by keeping your motor leads as short as possible and twisting the motor leads around each other in a helix.

Note: Even if your motor and logic power sources share a common ground, make sure you connect your motor power supply’s ground to the GND pin just above the VMOT pin. This ground pin is designed to handle the higher currents that your motors will draw; the ground pin above the VCC pin is not intended for high currents.

Related Products

Pololu Qik 2s9v1 Dual Serial Motor Controller
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