DIY CPAP Style BLDC

[ntwallace]

In addition to exploring off the shelf 12VDC pump motors, it seems worth recreating a CPAP setup with 3D printed/off the shelf parts. Mark Rehorst's printable blower (specifically v2) + a cheap BLDC looks like a good option.

[Diodeus]

Huh. I always expected the blower to be a positive-displacement vane pump.

[jcl5m1]

yes, this should work. Will add a link to the README.

[necro-nemesis]

It appears a centrifugal pump has been used for this application. I concur with exploring the use of off an off the shelf brushless DC motor and 3d printed pump solution. I can see limited access to sufficient CPAP pumps being a criticial factor. Brushless DC motors though should be more readily available as is access to 3d printed parts.

wrt to the controller wonder it there would be benefit in using an Nodemcu vs Arduino in order to add in wifi capability possibly for monitoring and ota programming.

I don't have a CPAP pump in hand to try and 3d model and adapt a brushless dc motor to the design. If anyone comes up with drawings I can work to adapt a brushless motor to I'd appreciate it. Also specs on the motor would be beneficial. I am scouring the internet now looking for something I can work with.

Other designs I have looked at incorporate 3 electrically controlled check values with the pump inflating a diaphragm. Not certain this is requirement if the Arduino can reasonably moderate the flow but in other designs it appear on exhale the airflow goes out a separate route through a value unobstructed. Would there be the need to add a separate route? Is it possible to stop the centrifugal pump rotor at a position in it's rotation during exhale to allow a passageway in the pump to be open at that point in rotation?

https://www.cpap-supply.com/Articles.asp?ID=134

[necro-nemesis]

This design may be worthy of consideration. https://www.thingiverse.com/thing:39755

[mrehorst]

I couldn't find the exact specs on the original motor used in the CPAP blower I copied, but I was able to find something close by the same manufacturer and determined that it was a 24W motor. I can modify my CAD file to accommodate any motor you might have, can scale up the rotor and housing for more air flow, too.

That Thingiverse design looks like it's made to pump water, and uses a brush-type motor- bad news around O2 because of sparks. Brush type motors wear out quickly. In the CPAP blower, the motor was located inside the blower with the moving air which probably helped to keep the motor running at a low temperature.

[necro-nemesis]

It was designed for air. You have a CAD design for the blower on the go?

[mrehorst]

https://a360.co/2I2Jz3Z

[necro-nemesis]

Yes for this to work I believe the approach has to be brushless motor for various reasons.

[necro-nemesis]

https://a360.co/2I2Jz3Z

Brilliant I'll have a look. How can I assist you? BTW I am able to 3d print in addition to work in CAD so if you need something physically built to check fitment and operation I am able to do that.

[necro-nemesis]

I also code and am conversant with Arduino.

[mrehorst]

The motor linked on amazon is rated 1120kV, 2-4S. If you use 14V to drive it (~4S), you'll only get it up to 16k rpm or so. The motor from the CPAP machine was at least 2000kV. The impeller needs to spin at 20-25krpm at maximum output (to match the CPAP blower- but was that sufficient output for a ventilator?). You want to find a motor that's rated for 2000-4000kV, and uses 3S or 4S battery, preferably with ball bearings for long operating life.

[necro-nemesis]

That sounds like a typical drone motor 2500kV if memory serves. I assume the power requirements of the motor will dictate the supply voltage and the Arduino would be powered at 5vdc using a buck converter off that supply to keep things simple. I was able to bring in your CAD files to work with them. I need to see if the motor is capable of 20-25krpm sustain operation. Unsure on this aspect.

[mrehorst]

I think this motor might be good: https://hobbyking.com/en_us/multistar-v-spec-1304-3100kv-multi-rotor-motor-ccw.html Not sure if the CW or CCW version is better- one of them has a left hand threaded prop mount...

[necro-nemesis]

Ha ha. You were looking over hobbyking at the same time I was. The issue with kv is that it doesn't take into account load so I'm not sure at this point how to calculate and apply the load to the equation. It may come down to some experimentation with a prototype pump. Should I commence building one from the drawings? I'm sure there will be several iterations built to get it adapted to ultimately the motor required. I have a couple here and an ESC to give me a baseline.

[necro-nemesis]

I have to dig. I have motor for an RC electric plane that might be suitable for testing. It has a single channel ESC with it I can hook to a receiver and run through it's paces on a bench. The drone motors I have on hand are 2250kv and 2600kv but I have a feeling this other one is bigger if I recall. Hard to imagine a CPAP machine would be as potent as what these motors deliver but possibly. I just have no basis to go by.