The BEC you mentioned is not for powering the motors; it is primarily for suppling logic power to the RoboClaw, though you could use it for other purposes (e.g. supplying power to encoders, potentiometers, or switches). The RoboClaw will power the motors with whatever voltage you supply it with via the main power input terminals.
By the way, 6V is the minimum operating voltage for powering the RoboClaw 2x7A, so even if you are using it to control 6V motors, my recommendation would be to power it from a higher voltage source so you have some extra safety margin. Powering your motor from a voltage higher than it is rated for will result in higher speeds and more torque, but it can start negatively affecting the lifetime of the motor, and it can also put the motor at higher risk of catastrophic failure when exposed to excessive loads. If you want to avoid that, you might consider limiting the duty cycle to keep the average applied voltage around 6V or using the RoboClaw’s built-in current limiting capability to keep limit the current draw to around 25% of the motor’s rated stall current.
The issue is the RoboClaw has a lower registered battery input than what is supplied with the DC power source when motors are running. For example, when 7VDC is supplied to the RoboClaw, the voltage drops from 6.9VDC to 6.5VDC proportionally to the motor speed. This was shown in the Basicmicro Motion Studio software and was also measured with a multimeter (at the main battery in/out pins). This was not expected behavior, as the two different power supplies showed a consistent 7VDC output.
Following your suggestion, I would like to limit the duty cycle and also limit the current draw to a safe level. Since I aim to use speed or position control with the motors, I guess I can make a closed loop reading the quadrature encoder values and modulating the PWM that is capped. However, I am not sure how I can sense or limit the current draw of each motor and would appreciate support on this matter.
The configuration software for the RoboClaw, Basicmicro Motion Studio, has “M1 Max Current” and “M2 Max Current” fields you can modify on the “General Settings” screen. Basicmicro Motion Studio also has a readout near the top of its interface that shows the current draw from the motors labeled “M1 Amps” and “M2 Amps”. I suggest reviewing the documentation from the RoboClaw user manual, and the links on the RoboClaw’s product page under the “Resources” tab should have other useful information.
