# \[Review request\] Support multiple printer fans

**URL:** <https://klipper.discourse.group/t/review-request-support-multiple-printer-fans/9327>\
**Category:** Developers\
**Created:** [July 6, 2023, 6:43am UTC](https://klipper.discourse.group/t/review-request-support-multiple-printer-fans/9327 "2023-07-06T06:43:01Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Viesturz](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/viesturz/32/4604_2.png) [@Viesturz](https://klipper.discourse.group/u/Viesturz)\
**Post date:** [July 6, 2023, 6:43am UTC](https://klipper.discourse.group/t/review-request-support-multiple-printer-fans/9327/1 "2023-07-06T06:43:01Z")

</div>

I’m working towards a less painful toolchanging suport in Klipper.  
And this is the first self-contained step that seems to make sense.

> <https://github.com/Klipper3d/klipper/pull/6282>
>
> Multi extruder setups can have separate part cooling fan for each extruder. This… change allows runtime switching between fans using ACTIVATE\_FAN command, similar to ACTIVATE\_EXTRUDER.
> 
> The fix is to essentially make \[fan\] the same as \[fan\_generic\] and use ACTIVATE\_FAN to specifcy which fan is the printer fan. Inactive printer fans may be manually controlled using existing SET\_FAN\_SPEED command.
> 
> This helps primarliy with PrusaSlicer gcode, that just emits M106 S110; T1; when changing tools. Making emulation with macros quite complex.

This adds support for multiple part cooling fans controlled by M106, in a similar way that multiple extruders are currently supported.

Feedback and general thoughts on toolchange support appreciated.

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<div class="post-metadata">

**Author:** ![Viesturz](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/viesturz/32/4604_2.png) [@Viesturz](https://klipper.discourse.group/u/Viesturz)\
**Post date:** [July 13, 2023, 10:25pm UTC](https://klipper.discourse.group/t/review-request-support-multiple-printer-fans/9327/2 "2023-07-13T22:25:34Z")

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Much silence. Friendly ping?

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<div class="post-metadata">

**Author:** ![dmbutyugin](https://avatars.discourse-cdn.com/v4/letter/d/e0b2c6/32.png) [@dmbutyugin](https://klipper.discourse.group/u/dmbutyugin)\
**Post date:** [July 25, 2023, 10:15pm UTC](https://klipper.discourse.group/t/review-request-support-multiple-printer-fans/9327/3 "2023-07-25T22:15:01Z")

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Do not take this as a discouragement of your work, but this specific pull request does add some code complexity, yet it claims that making the similar support through macros is quite complex. However, I’d say this should provide the same functionality:

```auto
[fan_generic fan_extruder]
pin: ...

[fan_generic fan_extruder1]
pin: ...

[gcode_macro M107]
rename_existing: M107.1
gcode:
  M106 S0
  
[gcode_macro M106]
rename_existing: M106.1
variable_active_fan: 'fan_extruder'
gcode:
  {% if params.S is not defined %}
  action_raise_error('M106 requires S parameter')
  {% endif %}
  SET_FAN_SPEED FAN={printer['gcode_macro M106'].active_fan} SPEED={params.S|float / 255.0}

[gcode_macro ACTIVATE_FAN]
gcode:
  {% if params.FAN is not defined %}
  action_raise_error('FAN parameter must be provided for ACTIVATE_FAN command')
  {% endif %}
  {% if 'fan_generic ' + params.FAN not in printer %}
  action_raise_error({'FAN=' + params.FAN + ' was not defined as fan_generic'})
  {% endif %}
  {% if params.FAN != printer['gcode_macro M106'].active_fan %}
  {% fan_speed = printer['fan_generic ' + printer['gcode_macro M106'].active_fan].speed %}
  M107
  SET_GCODE_VARIABLE MACRO=M106 VARIABLE=active_fan VALUE={params.FAN}
  M106 S{fan_speed * 255.0}
  {% endif %}

```

I didn’t test this myself, so I may have gotten some details a bit wrong, but you get the idea. And it appears to be simpler than the code changes in question. That’s just my 2 cents though.

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<div class="post-metadata">

**Author:** ![Viesturz](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/viesturz/32/4604_2.png) [@Viesturz](https://klipper.discourse.group/u/Viesturz)\
**Post date:** [July 26, 2023, 7:38am UTC](https://klipper.discourse.group/t/review-request-support-multiple-printer-fans/9327/4 "2023-07-26T07:38:50Z")

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Thanks for the input. Yes this can def be done by using macros. As can be almost everything short of core kinematics.

However this means overriding core gcodes and in my book should not happen on regular basis and is an indicator that their code should be updated instead.

I’m leaning towards that the core should support a certain set of setups without macros and as more marginal setups need increasingly more macros.

Fan is currently at a significant disadvantage when it comes to any multi extruder setup needing significantly more complex macro than other parts. Except perhaps MMU that is entirely different level.

I needed about 2 years of tinkering with Klipper to be able to write such a macro, so yes I consider that a complex one. I suppose we can add yours to the examples, but that means a user needs to:

- know it exists, since it’s not documented
- copy it into their config meaning no updates
- deal with any conflicts to other macros they might choose to copy.

Adding this to core klipper means better documentation, testing and support for all potential users. I can buy and argument that this is too narrow of a use case, but not that there is no benefit over macros.

If code complexity is an issue, I can simplify it significantly at the expense of not introducing postfixed [fan] configs.

Sorry if I sound fired up about this. I’m looking for a bit more structured feedback:

- is is type of change overall good fit for Klipper at this time, why?
- is the ACTIVATE\_FAN API reasonable. Should it accept the config name or fan name or both?
- is the implementation as extras appropriate vs macro example - discussed here.
- is allowing multiple [fan] configs a reasonable idea. It should we stick to fan\_generic? Maybe only allow selecting between [fan] entries?
- is the python implementation okay, any changes to be made there?