I’m doing research that will at some point need to use a Piezo Rotary Actuator (stepper) to control motion in a cryogenic vacuum environment. Fortunately there’s some time before that, but I could really use some help in getting some footing in how people actually control motors. My limited experience with electronics is from 10 years ago, so I’m coming at this fresh with my only related experience being some coding.
The task required is to:
rotate freely at a casual pace (~20rpm) until resistance is felt
push through the resistance at approximately 4-12 oz-in
manually instructed to rotate freely (~20rpm) back in the opposite direction
Extra notes:
Since the final version will use a stepper motor I would like to use stepper motors throughout and it also has to be dual shaft. Being able to adjust the torque at step 2 between runs would be really useful.
From what I’ve read it seems like my parts list should look something like:
NEMA 11 dual shaft stepper motor
Controller of some sort (which can be programmed by a computer using some provided software via usb?)
Driver if the controller can’t output the amperage needed by the motor
Power supply (probably less than 5V from what I can tell)
Some buttons to give the “start”, “return”, and “stop” commands?
Breadboard and wiring junk
Can a stepper motor perform the tasks that I’m asking it to do? I would assume that most stepper motors take an input of “make x steps” which leaves no room for controlling torque, so it would just push against the resistance (task step 2) at or near its stall torque? Can I use a potentiometer to downscale the input voltage to crudely control torque?
If anyone can provide some insight into things that I’m missing or resources to help me along, then that would be greatly appreciated.
You should be able to use steppers. You can write scripts for your moves, and some sort of a strain gauge to measure resistance. The speed can be programmed.
Perhaps a clutch of some sort to limit pressure? Stepper drivers often have a “reduced torque” state to reduce current while idling, so some sort of selection of motor current resistors could give you what you need.
NEMA 11 steppers? Maybe a 17 or 23. Not familiar with size 11.
A strain gauge could certainly be used to measure the resistance as there’s a spot where I think I’ll be able to slap one on. Good suggestion.
As for a motor current resistor, it seems like that approach would seek to do the same thing I had thought with the potentiometer. I believe the effect would be limiting the voltage over the motor, thus dropping current. However, I can certainly imagine that motor current resistors would be better at it, given that they’re designed for the job. I’ll definitely look into this and as I would prefer using an electrical approach to a mechanical clutch, as space on the device itself is limited.
You can’t just change the voltage, it likely won’t work. All that affects is the time to charge (L/R) of the stepper, the top speed of the motor.
The resistors I refer to are ‘sense’ resistors, so that the motor driver knows the current in the motor winding. LMD18245 stepper motor drivers employ these sense resistors.
We offer a few dual shaft stepper motors here: robotshop.com/en/stepper-motors.html
Ex: robotshop.com/en/rbsoy06-soy … =RB-Soy-06
The above is 36oz-in max, which is beyond the 14oz-in you indicated, and 6V nominal
If you need to operate it at 5V, it will provide less torque, but should still be enough for your application.
It is a unipolar motor, so ideally choose a unipolar stepper motor controller able to provide 1A+: robotshop.com/en/stepper-mot … llers.html
Most require input from a microcontroller (you choose which you want to work with), and you would connect the buttons to the microcontroller.
Power supplies: robotshop.com/en/robot-parts … l?limit=60
Torque control of stepper motors is not easy and you will really need to do additional homework.
