The fan web pages say they only need a motor with 1/250th of a horsepower, so it looks like my calculations above are off by 2 orders-of-magnitude .
Please let me know how to identify what motor+gearbox ratio will be appropriate to drive a 4" fan such as the one above at 3000 RPM as a constant load (until my batteries go dead ).
You could look at ducted fans for the RC world. Electric Ducted fans or EDF’s are used for jets. It might give you a lot of options. In my mind these could give you better response and can work off the shelf. Some come in cool colors too
Thanks much. I asked a co-worker about this, and he recommended a RC store, which I’ll visit this morning to see and learn about what EDF’s they have there.
If I can find a “weak” EDF, I’m imagining I’ll get 4 of them and mount them in a box-configuration pointing up and outwards from a common center, like the fingers of a hand reaching up to catch a basketball.
I’m imagining that this arrangement would be the most stable for catching/holding/suspending/guiding a balloon.
Actually, you want just one fan blowing straight into the balloon.
You can prove this to yourself by blowing up and into the balloon with just your breath. Blow steadily, not it spurts. You will find that a steady stream of air exerts a great deal of control, such that you can even have it 30deg or more off center and the balloon wont fall out of the stream. (This makes a great variation on the common kids’ party game of “keep the balloon up.”)
I returned from the store with their cheapest ducted fan, (tiny) controller board, and LiPo battery.
The Controller is called a ICS-300, made by GWS.
Their website is gwsus.com. They assume RC use, so they don’t say what waveform their ICS-300 expects. Instead, they just say, “Plug it into your RC receiver.”
What voltage and PWM range do these RC receivers generate?
The guy at the at the store suggested ~50Hz at 5V, but I thought I’d seek a second opinion what I should have my microcontroller send it before accidentally smoking the part.
To cut to the chase, which sort of uC output pin should I hook this to, and what should my program direct that pin to generate?
You control it the same as a servo. 50Hz is correct, with 1-2ms pulses. 5V is fine for the signal, and it should work down to (nominal) 3.3V.
The ICS-300 is also a BEC, so it’s power wire on the three pin header is designed to supply power to the receiver. If you don’t want that, you need to disconnect that line.
This ESCs has a simple safety features built in, such that it wont start running until it receives lowest throttle position (probably ~1ms) for about a second.
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