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I'd like to use an EV3 brick to power an old 9V motor (74569). To do so I'm going to get one of these conversion cables (x1676) but I'm not 100% sure if it's possible to control the speed of the motor with it. I'm aware of the limitations of these cables but RPM control is crucial to my project. These cables became quite expensive nowadays so I don't want to waste money on them.

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  • Hi Adam, I have provided a link to the conversion cable you are asking about, but I can't find any motors or other parts with the 74569 identifier. Could you please check if you got the number right, or alternatively link the motor similarly?
    – zovits
    Feb 22, 2021 at 15:16
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    @zovits, 74569 is the lego id for the 9-V motor, see here: philohome.com/motors/motorcomp.htm
    – Michael Verschaeve
    Feb 22, 2021 at 15:51
  • @MichaelVerschaeve thanks, neither Brickset nor BrickLink knew about this ID, which is quite strange. I have added the relevant link now.
    – zovits
    Feb 22, 2021 at 16:20
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    Does this answer your question? Lego RCX to NXT converter cables not working properly with EV3
    – David Lechner
    Feb 22, 2021 at 17:08
  • Not entirely a duplicate imho, the other question and answers do not reflect on suitability for speed or positional control.
    – Michael Verschaeve
    Feb 22, 2021 at 20:59

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You'll be able to control the 9V motor as an unregulated motor with the similar named motor block, you'll be able to set the speed approximately, but any accurate RPM control is out of the question as there is no feedback pulse signal from the motor to the EV3 telling it how fast it is going.

Also there are some programming quirks with this cable and an EV3, like having to specify two motor blocks as the first one is ignored, but I don't recall the specifics.

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  • This is correct. Emphasis on the fact that the cable will work as expected, but the motor is inadequate for OP's purpose. A motor with no encoder can't provide any feedback. Also, this details the "programming quirks" that were mentioned: bricks.stackexchange.com/a/15342/6720
    – MindS1
    Feb 22, 2021 at 20:39

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