I am attempting to drive my stepper motor to a speed of about 0.5 rpm using just the Tic Control Center. The goal is as smooth of movement as possible since it is moving a piece of analytical equipment that is taking a video of a drop of water on a surface so even small vibrations could jostle the drop. I do not know much about stepper motors, so after some tinkering I have set the Tic to these settings:
- Step Mode - 1/256
- Current Limit - 931mA
- Decay mode - fast
- All the other settings are set to default
When I rotate it at 200 pulses/s for example, it rotates very smoothly but makes a pulsing noise and jitters ever second or so, its almost like it sounds like its ramping up and then down and then it kind of clicks and stutters a tiny bit. I assume that that is the microstepping and the jitter is between the actual full step points of the motor or something like that, but im just guessing. I assume there are settings I need to change but I don’t know how to make this work. Thank you for any help!
Hello.
Could you post more details about your setup, like what power supply you are using and how you are controlling the Tic? Also, if you have any kind of load attached to the stepper motor shaft, I suggest removing that for now. Since your desired motion is pretty slow, it might be helpful to use a piece of tape on the shaft as a flag to help visualize the motion.
A video showing the behavior you are describing would be helpful too. Please note that the forum does not allow users to post very large videos, but it does work well with videos linked from other sites (like YouTube or Vimeo).
Brandon
Hi Brandon, here are some details:
- here is a link to a video I took: Pololu Stepper #1472 w/ tic 36v4 - YouTube
- I hope you can see what i meant by the stuttering, its like it is chugging and the stutter happens every 2 chugs, if you look closely you can see it in the video!
- Power supply is a meanwell LRS-350-48, the tic is receiving ~46V at VIN
- I am currently controlling the tic with the Tic control center, but plan on transitioning to python
- The load can be seen in the video, it is on 2 bearings near its center of mass so the load is very little, it can be moved by very lightly pushing it. I would prefer to not disconnect it if possible as it was a lot of work setting up
I can do so if needed though!
Thank you again!
That movement doesn’t look especially jittery to me considering how slow it is going. I suspect the larger “stutter” is just an uneven step size (probably when approaching a full-step position). You mentioned wanting 0.5 RPM, but it sounds like you are only stepping at 200 steps per second, which is closer to 0.25 RPM. You might try running it closer to 0.5 RPM (~427 steps per second) to see if the motion looks smoother at that speed.
Also, the decay mode can have some effect on how smooth microstepping is, so you might try different modes to see how they affect the movement.
Brandon
Hi Brandon, Im still struggling to get an even velocity on my rotation. I have tried every decay mode and fast definitely seems the smoothest, but when I crank it up to ~300 or 400 steps/second it is very clearly oscillating in speed. As you hear the motor go between full steps the movement speeds up and then slows down and then speeds up and then slows down and so forth; Is there any way to get a consistent speed out of the motor so there is no variation in its velocity? Thanks for your help,
Alec
If you are just setting the target velocity through the Tic Control Center and leaving it, the Tic will be stepping at a constant rate (once it accelerates to the commanded speed). Are you actually noticing the speed oscillate or are you just going off of the sound? If you are seeing some kind of oscillation in the speed, it might just be that your stepper motor is missing steps.
It sounds like you are driving your 7.4V motor at 46V, which might be making it hard for the Tic to accurately limit the motor to lower currents (which is required during certain phases of microstepping). So, you might try reducing your operating voltage to something like 12V to 24V to see if that makes any difference.
In general microstepping is not always that great for getting smooth movement at low speeds, so if reducing the voltage does not help, you could consider gearing it down. You can find some discussion related to this in this thread.
Brandon
