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Lego EV3 set tacho-motor speed [message #1806711]

Tue, 14 May 2019 10:11

Mario Krizic

Messages: 6
Registered: April 2019

Junior Member

Hello,

Is there any way to set the motor speed for the Lego EV3 in 4diac? My application is working as expected during debugging, but when outA.motor.enable is called, the motor does not move. I have tried changing the speed manually in the file system, but got a "Permission denied" error even if the file was opened using sudo and write permissions were set. So it stays 0 after every start/reset.

From the documentation, I have seen that there is only a function block to read the speed, but not one to set it. Another thing I've found is that there is the option of reading and writing through custom access, but there is no fileWriter so I assume that is a QW block.

My question is now how to implement such a block that sets the speed to say 100 before calling enable?

I have tried using a QW block with PARAMS=/sys/class/tacho-motor/motor1/speed_sp and OUT=100, but then I get an error:
"terminate called after throwing an instance of 'std::length_error'
what(): basic_string::_S_create
Aborted"

I think I am missing something. Can somebody point me into the right direction?

Thank you in advance.

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Re: Lego EV3 set tacho-motor speed [message #1806713 is a reply to message #1806711]

Tue, 14 May 2019 10:43

Jose Maria Jesus Cabral Lassalle

Messages: 136
Registered: February 2016

Senior Member

You should use "pwm" with an QW to write the desired value -> outB.motor.pwm (QW writes the desired pwm, IW reads the actual pwm)

You're right, the fileReader and fileWriter are not in the IDE, this should be added

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Re: Lego EV3 set tacho-motor speed [message #1806715 is a reply to message #1806711]

Tue, 14 May 2019 10:52

Mario Krizic

Messages: 6
Registered: April 2019

Junior Member

Ok I found out that it is necessary to write to outA.motor.pwm in order to get the motor working. However reset does not stop the motor in my case, therefore it is necessary to set the pwm to 0 before resetting.

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