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    Coupling motors

    A question is often asked on LEGO forums: is it possible to couple motors to get more power? And if so, is it better to use direct coupling, or to use a differential based adder? As I was already in a motors testing campaign, I built the above contraption, allowing to couple two motors either directly or through an adder. Switching between the two modes is done by sliding the driving ring. Gearing and friction is the same in both modes (except for the differential gears not used in locked mode of course!), so comparison makes sense. We measure rotation speed of the composite motor (which is proportional to delivered mechanical power) under various torque (weight lifting).
     

     

    Torque
    (N.cm)

    Speed (rpm)
    Locked

    Speed (rpm)
    Unlocked

    Difference (%)

    PF Medium

    2.56

    328.3

    328.9

    0.18

    6.40

    239.9

    238.3

    -0.66

    11.5

    125.5

    123.8

    -1.34

    PF Large

    2.56

    315.8

    314.5

    -0.42

    6.40

    258.8

    258.5

    -0.12

    11.5

    184.3

    185.0

    0.33

    PF XL

    2.56

    197.1

    198.2

    0.54

    6.40

    184.1

    184.3

    0.10

    11.5

    165.8

    168.8

    0.60


    As you can see, there is essentially no performance difference between coupling methods... Of course this is meaningful for identical motors!

    The test results showing available mechanical power of coupled motors are here.

     

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