Hi everyone. I am trying to make a wind simulator for my sim racing system using Uno V3 and Adafruit Stepper motor V1.2. I currently have 2 120mm 12v brushless fans connected to the shield and a 12v mains power source wired into the board.
I have fan movement and they turn on when they are supposed to, but for a 200cfm fan I dont seem to get much flow when advancing through engine rpm and speed. Any information is greatly appreciated and just have to say this is the first ever project of its kind I have attempted.
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Hi Adam
For a fan to move 200cfm it has to have a supply capable of 200cfm. For instance if this fan was blowing air out of a room with all air entry points closed it would only be able to sit there and cavitate, that is blow nothing. If the entry points were only dimensioned to allow 100cfm into the room only 100cfm would come out.
An embarrassing situation at a country NSW TV site many years ago. The standby diesel generator had been installed in its room. The normal operation would be for the diesel to take outside air via a filter, across the engine, through the cooling radiator through an exit hole in the wall closed by flaps when the diesel was not running. At this stage the inlet hole had not yet been cut in the wall. Power glitch, diesel started. The doors to the room opened outward and because of the air screaming through whatever gaps it could find the doors could not be opened and the diesel just had to be let run until it ran out of fuel. As it was under no load it did not overheat so the over temp system did not shut it down. I might remark this situation was rectified at the first opportunity.
Getting back to your fan, even if it were sitting in the middle of a room you may find the air simply going round in circles from the front to the back giving the impression of no air flow where you expect it.
Cheers Bob
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Thanks Rob for the reply and story. So what I took from that was I have to have something feeding my fan ?
Thanks again.
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May I just add a note, when i power the fans up on a desk top the move a substantial amount of air, so could it be a powering issue or incorrect hardware I am using ?
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Hi Adam
Not quite âfeedingâ the fan but making sure the fan has adequate supply of air. Something like a pedestal fan in a room will blow air but the further away you get the weaker will be the âwindâ. The fan is blowing air but when you think about it the air is really going round and round within that room. If you want an air change (fresh air) you need an entry point and an exit point.
They probably are and if you are sampling close to the fan it will seem like a lot.
Probably more an environment issue. I doubt your hardware has anything to do with it if the fan is running at the expected speed. Of course if it is not running at the speed you want it to you need to fix that first. What I am getting at here is how much âwindâ you feel at the end of the day will be to do with fan speed and positioning.
My experience with fans has been mostly with transmitter cooling and I do know for certain the fan has to have 1) an adequate air supply and 2) the hot air has to be ducted away or the air WILL just go around and around and get hotter and hotter until something really melts. One facility I worked at had 4 plenums, each with a supply fan (speed controllable depending on demand) capable of 30000cfm. Not a bad wind. Total capacity 120000cfm
Cheers Bob
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Ok I get what youâre saying. Will set a few things up differently and retest. Thanks heaps again.
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Hi Adam,
Personally, I find wind and fluid mechanics to be far too hard to figure out theoretically so Iâd fall back to a few simple home experiments to see what performance you can get.
I think this is an excellent excuse for some CAD (Cardboard Aided Design) to bodge together a few cardboard ducts and see how much the perceived airflow changes by having different shaped ducts placed infront or behind your fans. If you can prevent that room-scale mixing from happening and instead get a good directional blast of air with some clever ducting I think youâll get the wind feeling you need with less fan power.
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I will definitely have to try a few other configurations. Here is me thinking power to fan and boom job done haha.
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Hi Adam,
While this conversation has mostly been (rightly) focused on the physical, it may be worth taking a quick look at the electrical too. Could you draw a quick diagram to show how youâve got everything hooked up?
I know brushless motors need controllers, and pulsing that on and off thousands of times a second may be tripping them up. Have you tried a really low duty cycle (like 1 a second) to determine whether the motor driver is happy to turn the fan on and off, then moving to higher duty cycles to see if you get the response you want?
Keen to get to the bottom of this one!
-James
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Hey James, i will do this weekend and post the drawing up. I donât get out often to use it only Sundayâs ! arghhh family life
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Hey Adam,
Have you tested the fans with a straight 12V?
Everyone has been on the money about how to get more âperformanceâ out of your fan. But there is one gotcha when it comes to the pure flow rate, that number doesnât take into account how far the air has to move.
The flowrate of a fan is calculated as the Area the air can move through[m^2] by the velocity of the air[m/s].
Keeping the flow tight is a surefire way to get it somewhere, this squirrel cage blower can get some good throw out of it!
Liam
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Hi Liam, i actually bench tested the fan with a 9v battery and it created an impressive amount of air just from that. So thatâs what got me thinking is it my hardware, am i using the wrong shield. I am using a program called sim hub that sketches the board for sim racing.
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Hi Adam,
Are you able to tap into the sketch that sim hub makes? The Sheild you are using pseudo varies the voltage (fast on and off pulses) so hardware shouldnât be an issue unless the current limit isnât high enough - do you have a spec sheet for the fans you are using? The Adafruit Stepper shield says 0.6A continuous
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