I’m looking in to designing a system that will wind/unwind from one roll to a second roll and then reverse direction to wind back to the original roll. This will be repeated about a dozen times, sending the web material back and forth.
I’m planning on using two 24VDC motors (one to drive each roll) and the G2 Dual high powered driver board to control the motors.
I am wondering if there will be an issue with current being generated on the unwind roller and feeding back into the driver board?
also, does it make sense or is it possible to utilize “brake” function described int he docs to help with the tension control. if so, what would be the best approach?
The current generated by the rotation of the unpowered motor should not be a problem for your motor driver, but it could be a problem for your power supply if you are using something other than a battery since many other supplies do not deal with reverse current well. If that is the case, then you might consider using one of our shunt regulators.
I do not understand what you are trying to use the braking functionality of the driver for. Can you describe your application more and what you mean by “tension control”? Some pictures or drawings of your setup would probably be helpful too.
Thanks for the reply. I’m using a Meanwell NDR-120-24 power supply, and spec sheet indicates it has overvoltage protection of 29-33 volts, so seems like it might be ok. Not sure how to determine exactly though.
I may be misunderstanding the braking functionality, but in roll-to-roll manufacturing one way to make sure the web (fabric or sheet material) is rolled nicely and doesn’t sag is to maintain some tension on the material via the unwinding roll, so it meters out in controlled fashion. Was envisioning being able to have the unwinding motor provide some level of resistance with the brake as the other one pulls.
There will inherently be some level of resistance from the unpowered motor in your setup due to its cogging torque (unless you apply some method to avoid that, like using a clutch), but I do not think the braking operation of our G2 High-Power Motor Drivers will be useful for helping you tension the material roll like you were envisioning. The braking operation of the driver just means that the outputs are shorted to ground when power is not being applied on the motor. That will add to the motor’s mechanical resistance, but it is not going to be something that you can dynamically adjust.
Thanks for your help. Hopefully the motor’s mechanical resistance will get us where we need to be for our testing.
Looking at the G2 board’s documentation it says the A & B connections to the motor short to ground when PWM is set to low (0V). I currently have my code set up to set the unwinding motor to low while the other is running. Do you think that is the best setting or would it be better to disable the driver?
Also, I was trying to spec out the shunt regulator you suggested. My 24V power supply lists over voltage regulation at 29-33V. I presume I want a 33V shunt. The motor has minimal documentation but lists 24V 15W 5K on the label. Would you recommend the 33V 15W shunt? https://www.pololu.com/product/3777
Putting the driver into its low-power sleep mode will make the driver outputs high-impedance (i.e. they will be floating), so if you find that the unpowered gearmotor in your setup is creating too much mechanical resistance, disabling the driver might be one way you could reduce that. But it sounds like you are expecting the main issue to be not having enough tension in your system, so you are probably better off leaving the driver enabled.
Typically, the set point voltage for your regulator should be about 10% above the supply voltage you are trying to protect, so we would recommend the 26.4V, 15W shunt regulator. If you use the higher voltage version with your supply then its over-voltage protection could just shut down the supply before the shunt regulator can dissipate any of the energy that caused the voltage spike.
I am not sure exactly what parameter the 15W label on your motor refers to, so it is hard to be certain whether or not the shunt regulator will be sufficient.