There are at least 3 types of Power fans: A) 2 wires (+, -) B) 3 wires (+, -, TACH) C) 4 wires (+, -, TACH, PWM)

A, B types:

For A, B types you can connect a H-bridge https://www.ez-robot.com/Shop/AccessoriesDetails.aspx?prevCat=9&productNumber=14 and you can control the fan with https://synthiam.com/Support/Skills/Movement-Panels/Dual-HBridge-w-PWM?id=16067 control.

it works similar to a continuous servo but is not a continuous servo.

C type: The fan has a embedded micro-controller, and the proper way to drive the fan is to use the PWM pin. Note: Some fan's PWM pin requires a high frequency i.e. 25Khz.  You can try connect the PWM pin to an EZB's digital pin and use the pwm slider: https://synthiam.com/Support/Skills/Pwm/PWM-Slider?id=16047 IF does not work due the frequency (EZB PWM is not 25Khz) you will need an arduino micro-controller  and code some custom firmware to generate the 25Khz frequency.

it works similar to a continuous servo but is not a continuous servo.

And one further suggestion is to remove the electronic pcb from a continuous rotation servo and connect it to a regular fan.

that way you use the servo pcb to control the fan speed. And in ARC you’ll just a regular continuous rotation servo control with speed for both directions

Both @PTP and @DJ Sures answers assume you want speed control on the fan.  For a simple on off, you just need a transistor (and potentially a voltage regulator or alternate power source depending on whether the fan can run on the same voltage you are providing to your controller).

Alan

Ha ha ya and Alan is right on that observation. The easiest solution is the most elegant

Thanks very much for details of the numerous options. This level of support is amazing!!!!!

Let us know how it works out for you

Here's a thread on this forum that explains and shows how to do this with a simple transistor like Alan suggested. I have quite a few of these ion my robot and they work great:

https://synthiam.com/Community/Questions/Tip120-Tip122-Transistor-Switching-Circuit-9239

You could also use a relay and simply turn it on an off with one of the digital ports on an EZB or iotiny. One like this: 5v relay