Synchronous DC Motor

Thread Starter

CStreb777

Joined Jun 23, 2021
11
Hello all I have a control loop with of a motor that lifts a load. When I have a filter of 0.35hz on the loadcell, my load goes up and down smoothly with the control loop using 100lbs. when I set it to 0.7hz, I feel oscillations, in fact, when i go real slow, it almost feels like a stepper with 100lbs, with 40lbs works fine. I don't feel oscillations with 100lbs with the 0.35hz loadcell setting. so it appears i have a resonant frequency in the system with heavy weights. any suggestion on how to eliminate this? or isolate it
Thanks
 

shortbus

Joined Sep 30, 2009
8,971
Do you really have a DC synchronous motor or do you have a PMSM? DC synchronous motors were very large old motors, but the PMSM is more like a brushless DC(BLDC) motor. If it is the PMSM type motor, they will "cog" just like a BLDC motor if the speed is too low. The cogging effect is what it sounds like you have , from the very small amount of information given.
 

Thread Starter

CStreb777

Joined Jun 23, 2021
11
Do you really have a DC synchronous motor or do you have a PMSM? DC synchronous motors were very large old motors, but the PMSM is more like a brushless DC(BLDC) motor. If it is the PMSM type motor, they will "cog" just like a BLDC motor if the speed is too low. The cogging effect is what it sounds like you have , from the very small amount of information given.
i have an inmotion asm103 PMAC brushless motor with 25to1 gear ratio
 

Thread Starter

CStreb777

Joined Jun 23, 2021
11
the other motor type that seems to work is the https://www.br-automation.com/ 8LS series 8LSA36 R0045D300.
This is a working motor. I am new to motors and dont understand the differences. i believe this motor as lower inertia. There is no good data out there to look at,
 

MaxHeadRoom

Joined Jul 18, 2013
23,945
When using a BLDC or similar PM motor, it is imperative to use a suitable PID loop between motor and controller, ran open loop they 'cog' very noticeably at low RPM.
With the correct control, I have used them in CNC machining where cgging would not be acceptable.
 

Thread Starter

CStreb777

Joined Jun 23, 2021
11
When using a BLDC or similar PM motor, it is imperative to use a suitable PID loop between motor and controller, ran open loop they 'cog' very noticeably at low RPM.
With the correct control, I have used them in CNC machining where cgging would not be acceptable.
as i have mentioned with a low pass filter of 0.35hz measuring the load, oscillations isn't an issue, but not very responsive. i need at least 0.7hz to get good responsiveness but it gets jerky with 140lbs, actually scary, a bit. i am trying to figure out how to tune or at least look at the response.
There is a pid control loop in the controller for the inmotion motor. I just send velocity commands.
i am waiting on instructions for a tool to talk and tune this controller, canbus based, i dont have access to the constants via canbus currently

i have a embedded controller sending set points to motor controller w pid, for motor

do you think i need a pid in the embedded system?

APS3-Datasheet-rev-9.pdf (evs-inmotion.com)
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
23,945
I have used similar BLDC motors as those, but I have used a motor controller where I can tune the PID loop directly in the controller and using a simple trans-conductance amplifier/drive.
 

shortbus

Joined Sep 30, 2009
8,971
i have an inmotion asm103 PMAC brushless motor with 25to1 gear ratio
You still haven't really told us what you're attempting to do here.

But something I was taught back when electric motors were first replacing horses(a joke), was to choose the gear box to fit what your doing. You say you have a 25:1 gear box, but what is the average RPM of the motor verses the RPM you want the output shaft to turn? If the desired output is lower than what will be supported by the 25:1 gear you will have to slow the motor way down. Slowing this type of motor too much leads to cogging/jerking motions like you described in your first post.

All motor drives for a machine must be made with all things thought out, not just putting a group of parts together that may not play well together.
 

shortbus

Joined Sep 30, 2009
8,971
i have a motor lifting via a belt 140lbs of weight.
Can I ask a dumb question? Why choose a motor more commonly used for power steering in a car for this. This, the power steering comes from your link to the motor. 140 pounds seem like way more than a power steering motor should be capable of.
 
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