Is it possible to model this DC motor with the provided parameters on LTspice?

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
I am interested on modeling this DC brushed motor on LTSpice, however, after looking online I feel that the datasheet lacks a couple parameters necessary to model it. I am interested on being able to model it since i am about to begin building a control system with this motor. any advice or guidance will be greatly appreciated.
1657586641520.png
 

ronsimpson

Joined Oct 7, 2019
2,246
I think I know what to do about current and voltage. How are you going to set the RPMs?
Do you need to enter torque removed from the shaft?
Do you care about Back EMF? Engine braking?

Do you need to go through a startup sequence?
-start at 0 RPMs 120V and 64.5A--in some time the RPM will head toward to 3500 and "0 current". ??? (0 current??)
 

crutschow

Joined Mar 14, 2008
30,431
One big question is how will you simulate the motor load (which may be non-linear) vs. motor speed.
If you built a control system, you will need to know all the static and dynamic characteristics of the load.
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
One big question is how will you simulate the motor load (which may be non-linear) vs. motor speed.
If you built a control system, you will need to know all the static and dynamic characteristics of the load.
The load will pretty much be a load cell, which will be used to test materials
 

Irving

Joined Jan 30, 2016
2,979
The load will pretty much be a load cell, which will be used to test materials
That doesn't make much sense to me, you need to expand on what you're planning. If your goal is to, for example, test tensile strength by elongation then your motor is, probably, driving a leadscrew that provides the tensile force. The load is the material under test together with the gearing effect, and losses of, the leadscrew. The loadcell that measures the applied force is not the load.

In this, and similar scenarios, most of the dynamic characteristics of the motor are irrelevant. What is relevant is the gearing of your system and the power/torque output of the motor. Modelling the dynamics of motor is of little benefit. Assessing the suitability of the motor becomes a simple matter of applying some basic mech eng equations.
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
That doesn't make much sense to me, you need to expand on what you're planning. If your goal is to, for example, test tensile strength by elongation then your motor is, probably, driving a leadscrew that provides the tensile force. The load is the material under test together with the gearing effect, and losses of, the leadscrew. The loadcell that measures the applied force is not the load.

In this, and similar scenarios, most of the dynamic characteristics of the motor are irrelevant. What is relevant is the gearing of your system and the power/torque output of the motor. Modelling the dynamics of motor is of little benefit. Assessing the suitability of the motor becomes a simple matter of applying some basic mech eng equations.
Thank you, your response really cleared some of the misunderstandings I’ve had.
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
You're welcome. If you would like to explain what you're trying to achieve maybe I can give you more input...
Definitely, so i am working on a motor control circuit for a tensile strength machine. I just want to make sure I have all my bases covered, and would like to know if there’s anything different when designing a motor control system for such machine vs another application. The given motor has presented many challenges in terms of control.
 

Alec_t

Joined Sep 17, 2013
13,043
would like to know if there’s anything different when designing a motor control system for such machine vs another application.
I don't know how you're using the motor to apply tension, but if the motor is allowed to stall, or nearly stall, the current it draws will go up a lot from the rated value.
 

Thread Starter

rfengineer28

Joined Apr 28, 2021
71
I don't know how you're using the motor to apply tension, but if the motor is allowed to stall, or nearly stall, the current it draws will go up a lot from the rated value.
It’s not supposed to stall, but if this is the case then this becomes a problem about designing the board properly to handle the stall current right? Correct me if I’m wrong.
 

Irving

Joined Jan 30, 2016
2,979
Definitely, so i am working on a motor control circuit for a tensile strength machine. I just want to make sure I have all my bases covered, and would like to know if there’s anything different when designing a motor control system for such machine vs another application. The given motor has presented many challenges in terms of control.
Well unless you are planning to do hi-speed dynamic stress/strain measurements there is little inertial consideration required. Depending on the materials being tested - and therefore the force required - the main control aspect is accuracy of positioning since what you're measuring is ΔL/L v force. So your leadscrew pitch and your associated gearbox gives you a torque multiplier and a speed reduction. As long as the output force requirement doesn't exceed the torque rating of the motor or gearbox and doesn't exceed the buckling strength of the leadscrew the main considerations from the motor control aspect is amps v torque (you should never hit the stall limit, or bail out before you do) and control loop response in terms of ability to stop and brake the motor either:
a) when the desired max strain ΔL/L or tensile load is reached (assuming the leadscrew doesn't back-drive); or​
b) when the sample breaks (assuming destructive testing required) in which case the load vanishes and you need to stop the motor before it free-runs into the end-stop (consider a limit switch option here).​
What challenges?
 

Danko

Joined Nov 22, 2017
1,392
Definitely, so i am working on a motor control circuit for a tensile strength machine. I just want to make sure I have all my bases covered, and would like to know if there’s anything different when designing a motor control system for such machine vs another application. The given motor has presented many challenges in terms of control.
Feed motor from controlled current source, then you will easily and accurate control torque
and motor in this case can be even in stall mode, if needed.
 
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