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[rickh]

I saw an interesting link to a video (Way of the Wrench) on Discord about building an under cabinet blower.  This system uses a duct that routes under the cabinet and goes to the front so that the vent is placed directly under the coin door.  This is a brilliant idea, as I don't like the aesthetics of having an axial fan on top of the back box.  The fan for this project is the ducted axial variety, specifically used as a marine bilge blower fan.  It is rated at 130CFM with a 3" (~75mm dia.) aperture on both ends.  This fan is mounted inside the cabinet requiring a 2" (~50mm) diameter hole.  An adapter fitting is used to reduce the 3" down to 2" through the hole.  Underneath this 2" hole is a rectangular duct that appears to be 3" wide (75mm) by 1" (25mm).   This duct runs about 6" to a telescoping 90 degree elbow with a vent on the opposite end.  This vent points upwards toward the player, directly underneath the coin door. The slight flair of the vent allows a flood of air ensuring the player is immersed in it.   

I'm going to digress for a moment to explain fluid dynamics 101 and compare it to electricity. CFM or air volume is analogous to Electrical Current, Static Pressure is analogous to Electrical Voltage, Air Ducting (including the aperture reducers and 90 degree elbows and vents) are analogous to Electrical Resistance and Air Velocity is almost (I'm going out on a limb here) analogous to electrical Watts.  To transmit air through a network or ducting requires lots of static pressure much like electrical power lines require very high voltage.  Air resistance is the enemy of air volume (CFM), the Reducer Adapter and two Elbows used in our example drastically reduce CFM and if there is substantial static pressure, it produces or increases air velocity (speed).  This is why every house that has an HVAC system uses a centrifugal blower instead of an axial fan, as it produces more static pressure rather than CFM. While Axial fans are optimized for pushing large amounts of air through an open space they are not suited for pushing air through a network. 

 

While this fan/blower is extremely effective, it does have a couple major flaws. 

• A large 2" hole is required to be drilled into the cabinet bottom.  This is a full commitment.
• The large ducted fan takes up valuable real estate inside the cabinet. 
• A ducted axial fan loses a lot of efficiency in a ducted system with two 90 degree turns

 

So, I took another approach and used a flat 33mm high pancake centrifugal blower.  It has less than half the rated CFM of the ducted axial fan and half the power, but it has slightly more pressure.  In effectiveness it produces less air flow, but almost the same velocity. 

To make this implementation effective I designed an adjustable vent to focus the air directly at the player.  The original design used a shotgun approach, a flared vent that disperses the air to a wider area.  I also added a vent cover that automatically closed over the vent during non usage to preVENT any garbage from falling into it, hence becoming a flying projectile.   The .STL files and fan specs are on my GitHub at www.github.com/rmhorwitz/Pinball-Blower-Toy .  I am also playing with a much bigger fan that is slightly more powerful than the ducted axial fan.  This increases the Z by 10 mm.       

Here are a couple photos of this system:

Edited by rickh, 28 March 2026 - 07:00 PM.