Ideal Torque and Rotational Motion Sensors
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I am trying to monitor the angular velocity and torque generated by a brushless DC motor. I am using the 'elec_brushless_dc_motor' example as a reference. The Ideal Rotational Motion Sensor block is an "across variable" block, so it should be hooked up in parallel to the motor and driver. The Ideal Torque Sensor block is a "through variable" block, so it should be hooked up in series with the motor and driver. As you can see, I have done this. However, the Ideal Rotational Motion Sensor block doesn't report any angular velocity (0 rad/s). There are no issues with the torque block, it reports the torque correctly.
What am I doing wrong?
Accepted Answer
Sebastian Castro
on 7 Mar 2016
0 votes
The setup of Through/Across looks correct. The problem may be with that "Goto" block.
By default, Goto blocks have a "tag visibility" parameter such that the data is local only to the subsystem that the block is in. If you change this from "local" to "global", does it fix the visualization of that velocity signal?
- Sebastian
14 Comments
Jonathan
on 7 Mar 2016
Sebastian Castro
on 7 Mar 2016
Edited: Sebastian Castro
on 7 Mar 2016
Oh, wait. I see the problem!
The R and C ports are directly connected to each other, so that whole thing is hooked up to ground. This is why you get zero motion.
What you want to do is use that Torque Sensor to measure the force flowing in/out of any Inertia blocks at that node... which hopefully are inside that "Motor and Driver" subsystem.
To rephrase: That Torque Sensor block is causing a "short-circuit" between R and C, where C is connected to ground. So, both R and C ports are constrained to have zero velocity.
- Sebastian
The output of the "Motor and driver" subsystem comes from a Servomotor model from the SimElectronics toolbox. The Servomotor has an inertia parameter of J = 5e-10 kg*m^2. So yes, the "R" port does have an inertia tied to it.
I simply want to get the torque and rotational speed PS outputs from the Servomotor. What is the most standard way of doing this with the blocks that I have laid out.
Jonathan
on 7 Mar 2016
Jonathan
on 7 Mar 2016
Maybe it helps to have context. I am trying to drive a revolute joint on a quadcopter model. The torque generated by the Servomotor model is used to drive the revolute joint modeling the propeller connected to the brushless DC motor.
What is the best way to hook this up?
Sebastian Castro
on 7 Mar 2016
(Sorry for the confusion, I kept editing my posts while you were responding)
The original Torque Sensor block is causing a "short-circuit" between R and C, where C is connected to ground. So, both R and C ports are constrained to have zero velocity.
So, what you want to do is stick the Torque Sensor inside that subsystem, to be in series between the Servomotor's R port and the connection port #5.
On the top-level, the R and C ports should not have a line between them.
Sebastian Castro
on 7 Mar 2016
Edited: Sebastian Castro
on 7 Mar 2016
Also, to answer your second question, connecting Simscape to SimMechanics shouldn't be a one-way connection. That is, you can't simply feed the motor torque to the SimMechanics model without applying the SimMechanics velocity back to the motor... the Simscape motor needs to know about the mass on the SimMechanics side it needs to accelerate.
This two-way connection can be done with standard blocks, but you can also download pre-made "interface blocks" from the following File Exchange entry:
- Sebastian
Jonathan
on 7 Mar 2016
Jonathan
on 8 Mar 2016
Sebastian Castro
on 8 Mar 2016
Those connections look right.
The quad is spinning when you drive the motors, so that's good. Not sure if this is the behavior you expect to see or not, but at least the model is connected right now.
- Sebastian
Jonathan
on 9 Mar 2016
Sebastian Castro
on 9 Mar 2016
Edited: Sebastian Castro
on 9 Mar 2016
Those warnings just look like version incompatibilities.
If you save the library file in your version and try again, those warnings should go away... hopefully.
Either way, that won't affect your simulation at all.
Jonathan
on 9 Mar 2016
Jonathan
on 24 Mar 2016
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