After reading the documentation on the Jrk motor controller I was wondering if there was an analog interface that I could connect between my Maestro and the FB (feedback) pin on the Jrk. The goal is to use a brushless motor for position control using the Maestro?
I am using the Maestro and would prefer not having to convert to a micro controller.
All help is appreciated, thanks.
Hello.
Neither the Maestros nor the jrk motor controllers can directly control a brushless DC motor, so it is not entirely clear how you want to use them in a system together that does that. If you tell me more about the rest of your system (like maybe you are planning on using an ESC) and application (a schematic of your proposed connections would help), I might be able to make some suggestions.
-Jon
Hi Jonathan, My error, I meant to say brushed DC motor. I wrote a computer application using the maestro SDK and currently, I have a setup that uses a Maestro controlling 8 servos and I am currently using an 18v7 simple motor controller for each motor connected to the remaining channels. I am finding it too difficult to control the motors by judging speed and duration. So positioning the motors using an RC interface would solve my dilemma.
After reading about positioning using the analog setting for the FB pin on the Jrk, I thought maybe there might be an interface that would convert the RC signal from the maestro to an analog signal to drive the FB pin on the Jrk.
Right now I am experimenting with the Tic T825 which I just recently purchase. My only concern with the Tic is it’s minimum 8.5V power requirement (I am using 7.2 as my standard) and the extra power consumed by the stepper motors holding their positions. So brushed motors seem to be the way to go.
Thanks, Randy
You could use the Maestro to generate RC signals, which the jrk can use as an input to control a motor. Those RC signals can control a motor with or without feedback. The jrk has a single feedback pin, and it can use the frequency from speed measuring devices, like a tachometer, or analog voltages from something like a potentiometer. So, if you want to use feedback, then you would have to connect something like a tachometer or potentiometer to the output of your brushed motor. You can learn more about the jrk’s feedback under the “Feedback Options” section of its user’s guide, which you can find under the “Resources” tab of its product page.
The interface you described “that would convert the RC signal from the maestro to an analog signal to drive the FB pin on the Jrk.” would not work. A key aspect of a closed loop control system is to use measurements of the actual output (which in practice is different from the commanded output) to update the input. You can read more about PID controllers like the one used on the jrk in this Wikipedia article.
Both the Tic and jrk motor controllers can be controlled with hobby RC signals that the Maestro can generate. If you tell me more about your application, I might be able to help you decide if a stepper motor or brushed DC motor is more appropriate.
-Jon
Hi Jonathan, thanks for the explanation on the Jrk controller.
My current setup uses the maestro with an 18v7 controller and a Titian 550 brushed motor. This meets my requirements for speed and torque however, maestro frames are difficult to create since we have to carefully calculate speed and duration and then create a following frame to stop the motor. The Tic T825 works great when positioning a stepper motor with the maestro. But I have discovered that torque is greatly reduced at higher speeds using a stepper motor.
My problem is: how do I use the Maestro to position a brushed motor like the Tic works for a stepper motor? I understand that a maestro channel can be set for digital output. Is there a way to take advantage of that?
Thanks, Randy
It sounds like you are coming across some fundamental differences between stepper and brushed DC motor control and behavior. Stepper motors are mechanisms that are specifically designed to perform small rotations at discrete angles (i.e. steps) and brushed DC motors are designed to continuously rotate. So, to get a brushed DC motor to rotate to a specific position, you would have to build a system around the motor (e.g. use a potentiometer at the output shaft) that incorporates feedback about the position. This is basically what a hobby RC servo does, and you could use the jrk with its feedback mode set to Analog to make your own custom servo. (As an example, this Torxis servo uses one of our jrk motor controllers.)
Using a Maestro’s channel as a digital output is not likely going to help control a brushed motor more like a stepper motor since it could only output 0V or 5V, and the Maestro’s channel cannot handle the kind of current needed to drive a motor. A single digital pin is not really a useful interface used for controlling motors, either, unless it is capable of generating PWM signals.
-Jon
