stepper motor resistance for soft based limits

Other Hardware Motors, Mechanics, Power and CNC
1

is there a way to track a stepper motor resistance to know when the motor has reached it's min/max rotation limit.

basically my stepper motor is connected to a adjustable damper that has a can only be rotated (depending on model) between 5 and 7 rotations.

what I am trying to do, is via software drive the stepper counter clockwise until it hits this physical limit in the damper (set 0 step), drive clockwise until limit while counting the steps. finally supplying the number of damper settings/total steps I can calculate the damper position.

i just don't know how to find min/max travel

2

Try to measure the current when the motor stalls.
You could have a small resistor in series with one of the stepper coils and measure the voltage being produced by the current flow. When the motor stalls it should increase and you can use this rise for triggering actions.

3

You need a limit switch to detect the end of physical travel.

4

Your description of what you want to do is not very clear.

A stepper motor applies its full torque all the time so there is no simple way of detecting a stall.

A complex solution would be to put a rotary encoder on the motor shaft to count steps. If the number of steps commanded is greater than the number counted by the encoder you would know that the motor had stalled.

If the thing the motor is pushing against is fixed and could have a limit switch attached to it that would be a much simpler solution.

...R
Stepper Motor Basics
Simple Stepper Code

5

limit switch won't work, think of screwing a nut and bolt together, there is a unknown number of rotations in either direction before the bottoms out or removes out of the threads.

6

OK. But I still don't have a clear picture in my mind of what you are trying to do. Maybe you can post a diagram?

Are you trying to use the motor to keep turning until a specific torque is achieved - like using a torque wrench?

If so it may be that a simple DC motor would be more suitable as there is a relationship between current and torque.

...R

7

before the bottoms out or removes out of the threads.

Whatever that means, a limit switch can almost certainly be arranged to detect it.

8

attached is a quick and dirty diagram

Drawing1.png
Drawing1.png636×610 23.9 KB

9

Image from Reply #7 so we don't have to download it. See this Image Guide

e159c335a2b03292dbbffd9c27da9494baf79975.png
e159c335a2b03292dbbffd9c27da9494baf79975.png636×610 23.9 KB

...R

10

Am I correct that you want to drive the adjustment screw on the damper to its limit without first knowing how many turns that might require?

If so I presume the stepper motor is intended to stall when that limit is reached.

And if my surmise is correct I think the only way to do it is with a rotary encoder on the motor shaft as I mentioned in Reply #3

If you have to go to the trouble of using a rotary encoder it may be simpler to use a DC motor.

...R

11

A stepper is possibly the right choice for this, but you must be able to control the current that is driving the stepper. Using an A4988 or DRV8825 type of chip, you can set the current limit so that the stepper only has a specific torque available. Then just drive it a thousand steps or whatever.

12

If you know which model of dampener you are using and the number of max turns, limit the torque and run it a full 600 pulses or what ever is required for a full stroke and work backwards from there. a stepper would work perfect in this application. by doing this in your setup it will reset the position every time it is powered up. I believe MorganS is saying the same thing.

13

You may try to mount the stepper directly inline with the adjustment screw if you have the room. Maybe a coupler made from a deep socket?