Servo on Fan output

  • I am in the process of building my custom made toolchanger.
    For this I use a TowerPro MG90D digital servo connected to my Duex5.
    Everything works fine but there is one thing that is bugging me. I would like to completely turn off the servo after a toolchange. If I just disable the PWM output by sending M42 P3 S0 the servo does not deactivate and "holds" the current position and the servo gets warm after a while.
    I was thinking to move the servo power connection to one of the FAN outputs and control that output to cut the power to the servo:


    Would this a feasible idea?

  • Anyone, @T3P3Tony or @dc42 ?

  • Would have to switch the V-FAN jumper over to 5V AUX.

    Code in your tool change macro might look something like this:

    M106 F7 S255 ; turn fan on full power
    M280 P3 Snnn In ; servo command
    G4 Pnnn ; wait nnn ms for command to execute
    M106 F7 S0 ; turn fan 7 off

    It might be possible to unmap the fan and instead use the M42 command, something like this, not sure the practical difference

    M106 F7 I-1 ; disable fan 7 (to open up pin for general purpose use)
    M42 P27 S255 ; set pin27 to 255 (power on)
    M280 P3 Snnn In ; servo command
    G4 Pnnn ; wait nnn ms for command to execute
    M42 P27 S0 ; set pin 27 to 0 (power off)

    Note I haven't tried any of this but it might work 😄

  • @nhof : I finally had some time to try this out and it works like a treat. Thanks!!! 😉

    Unlock tool macro (using Fan3 and PWM1 connector):

    M42 P23 S255
    M280 P3 S70
    G4 P500
    M42 P23 S0
    M42 P3 S0

    Lock macro is the same, only servo value changes

  • Did you pull power from the fan (and change it to 5v) or just use the switched fan earth to turn it off and on? Got 12v fans but like this idea as my servo got very hot when I tried this.

  • @oliverracing I did change to 5v instead of 12V and pull the power from the fan connector. I dont run fans on the duex so it isn't a problem in my case.
    I am not sure what you say will work, maybe @dc42 can acknowledge this.
    I am quite happy this works as my servo can stay cool now and only is powered when I actually change tools.

  • If this will work it's definitely of interest (Just running a base Wifi with no deux) to me as found it got hot enough to soften the ABS so had to abandon the design!

  • working on my own tool changer. does using PWN1 require disabling the heater channels?

  • administrators

    A common cause of a servo continuing to draw power when not moving is that you are commanding it beyond its maximum travel.

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