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Oct 21, 2014, 10:22 PM
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The ultimate travel fan

Inspired by the continued existence of a AA consuming toy fan from the 1980's, it was time to build something more efficient with RC parts.

Dumb Blond hottie

You wouldn't believe how hard it is to make a fan. The mane problem was noise, which RC parts aren't designed to avoid, but which is a critical design feature for appliances. The other problem was safety. A prop saver did absolutely nothing. The prop still shattered in an obstruction test. This is 1 area where 3D printing a shroud would be useful. For now, a wire provides some minimal protection from accidentally coming in from the side.

The speed was controlled by a simple PIC with leftover pot from a 360' servo conversion.

This didn't work. It was extremely noisy. The vacuum created in front of the wide wooden plank was the reason.

This silenced the cavitation noise nicely, leaving manely the PWM noise from the motor. Cavitation noise was still significant, but bearable.

PWM noise was extremely loud. The problem is the only portable power supply was a laptop brick, which outputs 19V. Reducing the throttle doesn't make the PWM noise quieter, since the coils always go all the way to 19V. You have to reduce the voltage.

The quietest voltage before ESC shutdown was 6V 3A. There was no voltage which could be used with 100% duty cycle. A 6V 1.5A E-flight brick made far less power than its rating. The CP33 brick at 12V 1A was the only easy supply that worked & it was also the most compact. has a 5V 4A, 6V 1.5A, & many 12V bricks. The noise at 12V remaned quite intense. Eventually the old Yamaha adapter stopped working, so even the switching bricks don't have fuses.

It's unbelievable that ESCs to this day still go at 16khz, but that is because of the inductance of the motor coils. Gave up on compactness & went for a 12" in puller configuration to reduce the cavitation again.

That was the absolute quietest, but motor PWM was still awful. It turned out the most expensive ESC in the apartment, a $99 Castle Phoenix 35, supported 24khz PWM. The oscilloscope showed it doing 35khz, but either way, it still made a squeeling sound. The squeeling sound was quieter still, so hopefully good enough.

The Castle had the highest idle throttle of any ESC, making it useless at 12V. 5V provided the most useful RPM range, with a maximum current slightly above 4A. The only power supply was a good old, gigantic PC power supply. The entire 12" fan with 35khz PWM on 5V was virtually silent. Outdoor use still requires a 12V battery, but outdoor use also requires a higher RPM.

Power supply options are 5V 4A wall mount:

or a high input voltage UBEC:

The BEC would handle either a 19V laptop brick or a 12V battery. The CP33 needs a new wall mounted 12V supply, anyway.
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