Hello,
I use two of your motor drivers (VNH2SP30 and VNH5019) on different projects. I optoisolate the boards because that dramatically attenuates noise going in to my microcontrollers. You should consider adding optoisolators to the mentioned drivers.
My project uses 3 batteries: one for the microcontroller, one for the motors (VIN), and another for the motor driver (VCC +5V). Question: I’d like to get rid of a battery - is it possible to power the motor driver with VIN?
randomvibe
I use the VNH5019 Motor Driver Carrier and power the logic supply for the motor driver from the same 5V supply used for the microcontroller. In general, you need only separate the motor supply from everything else.
Yes, that was my original setup. The issue with that is high noise injected into the microcontroller, specifically the ADCs for a tracking robot. Also got strange latency behavior (more on this in link below). All these issues went away when I optoisolated the microcontroller from the motor driver.
So back to my question, is it possible to supply driver power (VCC +5V) from the motor supply (VIN)? These drivers are pricey so I’d rather ask for confirmation first. Thanks.
Of course you can power the motor driver logic from the motor power supply. The same holds for the microcontroller (toy manufacturers do it all the time). But unless you employ proper voltage regulation, adequate power supply decoupling and proper grounding techniques, you are guaranteed to have problems.
Fortunately, both power supply decoupling and proper grounding are old, old problems with very well understood solutions. However, to apply the standard solutions properly you must fully understand the source and nature of the power supply noise, and due to its transient nature, you will need an oscilloscope to investigate.
For example, does the motor power supply voltage transiently drop below 5V, or are there voltage spikes large enough to destroy the logic supply regulator?
Hello.
Thank you for your suggestion about optoisolators; making drivers with some form of galvanic isolation (not necessarily optical) has been on our to-do list for a while now.
Jim’s advice sounds good. You should regulate to an appropriate voltage for the logic supply and take measures to prevent too much noise or voltage drop.
-Jon
Since Pololu knows their motor drivers best, can you suggest a more specific solution for using VIN to supply VCC with +5V? Is it as simple as adding a 1amp 5V regulator with a 1000uF low-ESR capacitor? The driver powers your Tamiya 72101 Gearmotor set. I appreciate your help on this. Thank you.
We do not expect the VNH2SP30 logic to draw much current, so while you could use a 5V, 1A regulator, you could also probably use a much lower power regulator, like this 5V, 300mA step-down. I do not know what value of capacitor would work best for that, but 1000uF seems like a good start.
Also, we have found that the Mabuchi FA-130 motors used in many of our Tamiya kits generate a lot of noise. You could help mitigate that by adding external 0.1uF capacitors across the motor terminals and between the terminals and the motor casing. You can learn more about the noise on those FA-130 motors and adding capacitors to reduce that noise in this post. Alternatively, you might consider replacing your motors with this lower power FA-130 size motor, which draws less current (and should produce less noise), though it looks like it will also produce lower torque.
-Jon
Jonathan: Thanks for pointing us to the post on FA-130 noise.
Nothing like an oscilloscope, to clearly show you something you probably never wanted to see!
Okay, the VNH2SP30 driver is now self powered with a 5V, 1A regulator and 1000uF filter connected to the motor battery. It seems to work. I was concerned that current spikes drawn by the motors would pass the the regulator and damage the driver. Is this correct?
I did not mention my motors - I use the Tamiya 72101 Gearmotor set (12A stall per motor) and bane bots RS545 (21A stall per motor). Serious motors with serious noise.
I purchased several “VNH2 Motor Driver + Tamiya 72101” combination deals here at Pololu. Any chance of it coming back, or a similar deal with high end motors?
Instead of placing the capacitor close to your battery supply, I recommend adding your 1000uF capacitor as close as you can across the regulator inputs. This should protect the regulator from voltage spikes and provide a smooth 5V to the VNH logic.
Those 72101 motors were discontinued by Tamiya, and while we are continually expanding our selection of motors, we have no immediate plans to carry similarly high-power motors.
-Jon
