The user guide for the SVP-324 indicates that the VBAT-VM1 and VBAT-VM2 connection on the PCB can be cut or removed. I copy the text from the user guide " By default, the motor drivers are powered from the external power supply (VBAT). However, you can disconnect the external power supply from the motor drivers by cutting the labeled traces on the bottom of the board (VBAT-VM1 and VBAT-VM2)."
I would like to connect the controller to 3V DC motors while using 6 - 9V for the VBAT. Thus, I need to disconnect VBAT from VM1 and VM2 and perhaps connect VADJ (after setting it to 3V) to VM1 and VM2 solder pads, however, I am not sure what needs to be cut as there seems to be no direct trace between the two solder pads (VBAT and VM1 or VM2).
If you look at the bottom side of the board you should see a copper connection between the through-hole labled VBAT and the through-hole labeled VM1 (or VM2). To disconect VBAT from VM1 (or VM2), you should make your cut between the two through-holes (perpendicular to the long edge of the silkscreen rectangle). Maybe you’re being thrown off by the thickness of the trace? Since this path needs to be able to carry a lot of current, the copper trace is fairly wide. If you’re still having trouble seeing it, let me know and I’ll make a quick diagram for you.
Although cutting the trace isn’t a big deal, I think, it would be a good idea to have a jumper in place of the trace (perhaps in future PCBs). It would provide an easy way to remove the connection between VBAT and VM1 (or VM2) and revert back to it when needed.
My students will be controlling the 3V DC motors in the next couple of weeks; I will surely let you know of the results.
The through-holes are there so that you can solder in a 2x1 male header after cutting the trace, which would let you use a shorting block reconnect VM1 (or VM2) to VBAT, or you could just bridge it with a piece of wire. We appreciate the feedback; we designed the board to have a lot of customization options, but most of them require the user to cut a trace and replace the cut connection with a jumper. The PCB is intentionally routed the way it is because we don’t expect these to be common modifications, and in general it’s better to have motor current going through a short, wide trace than a removable shorting block that could melt if you try to put six amps through it.
I was able to successfully use the 3V DC motor after cutting the VBAT-VM1 connection on the PCB and connecting the Vadj (which I set to 3V). The motor driver worked just fine! Even so, I am thinking of instructing my students not to cut the connection, but rather use the duty cycle of the PWM to control the average DC voltage applied to the motor. Let’s say, our V-BAT is set for 8V. Now, if we set our motor speed such that the duty cycle of the PWM is no more than 37.5%, then the average DC voltage would be 0.375 * 8 = 3V. Although this means that the DC motor will be having 8V for part of the PWM cycle, I don’t think it would adversely affect the motor, especially that the PWM frequency is in the KHz range. Someone could argue that it might shorten the life of the motor, but in my opinion, it would be tolerable!
Thanks for explaining the reason for keeping the VBAT-VM1 connection wide on the PCB, but I still think it would be a good idea to have your future PCBs designed to make or break the connection without having to cut a trace on the PCB. Perhaps a thicker jumper or a few of them in parallel, etc. Of course, this all depends on the need for it and the extra cost and effort. If as you indicated, not too many people would need this feature, it may not be worth increasing the cost of the robot controller for a feature that would not be needed in most cases.
Thanks for letting us know how it worked out. It’s good to hear that the motor drivers worked at 3V! Running the motors at a higher voltage limited to a lower duty cycle and running the motors at 3V should both have a similar effect on motor life, though capping the duty cycle at 37% will decrease your speed resolution.
