Compressor for 540 Motors (>1.0 psi !!!) by truglodite

Last crawled date: 2 years, 10 months ago

Yet another electric powered "turbo"... but this one sucks really hard! [>1.0 psi easily]
I set about designing a centrifugal compressor with a smaller rotor/shroud clearance that commonly found, in order to achieve high pressures more efficiently. With just 0.5mm clearance, this thing has enough clearance to work with common sloppy hobby grade hardware and printers, yet it is still tight enough to put out 1psi without much power. I achieved over 1psi on 2s5000 with the below listed 4000kV motor. I have tested with 3s without measuring pressure; it was pretty scary but it may be able to do 4s if have a better motor and balance the rotor well.
BOM:
1@ 540 sized motor (w/ 2-6@ M3-10 mounting bolts)
1@ printed rotor (ABS, 0.1mm layers, 4 walls, 70% infill, build plate supports)
1@ printed matching upper (PLA, 0.2mm layers, 2 walls, 40% infill, supports everywhere)
1@ printed matching lower (PLA, 0.2mm layers, 2 walls, 40% infill, no supports required)
6@ M3-16 bolts
*The type of upper and rotor must be matching. For example the V2 36mm rotor only fits the V2 36mm upper. The original lower housing fits both the original upper and V2 uppers. The V3 upper only fits the V3 lower housing.
Motors:
I tested with this motor-https://www.amazon.com/gp/product/B01DBS3MQQ/ref=ppx_yo_dt_b_asin_title_o02_s01?ie=UTF8&psc=1)
I would recommend finding a better 4000kVish 540 motor as this one is perhaps the worst quality motor I have ever owned (got warm and sounded like a pylon racer on my bench with 2s and no load... extremely poor efficiency and balance). To be honest you may be better off with a brushed 540 vs the one linked above. OTOH, if your budget is a little higher you can get something like this to make it absolutely scream:https://www.michaelsrchobbies.com/mrc4300-1-10-4300kv-sensorless-540-4-pole-motor.html
Printing:
Note that the rotor clearance is very small, and this will be turning high RPM. So print higher resolution (0.1mm layers) to increase overhang performance and layer adhesion. Even a PLA print will work OK. ABS is even better, and one up if you treat it with acetone vapor. I prefer ABS rotors as they are lighter weight, and can handle a bit of temperature if needed. SLA also works well if you have it. I made a rotor with 50/50 Siraya Blu and Fast Grey, no supports, and it came out nice.
I found that common infill settings will work OK (2x 0.4mm walls, 0.8mm thick top/bottom, etc), but for in use prints I prefer 40-50% cubic infill, with infill connected lines enabled. These settings usually produce a stronger and more durable part, versus the usual triangle infill ppl like to use on everything. With these settings you get better infill to wall adhesion, less infill telegraphing (less visible on the outside), and a lot less travel/retracts while printing infill as well. The parts feel stronger in all directions, but it does require a small amount of extra filament and print time.
Post processing:
The rotor shroud area of the upper housing must be cleaned up well after printing. If you leave behind loose strings or chunks of supports there, these may be dislodged during operation and cause damage to the rotor. Cleaning the inside of the volute (snailshell part) is not so critical.
Due to my decision to stick with common automotive turbocharger volute design, a lot of supports are required to maintain a smooth section in the volute. The original and V2 versions both require a bit more support material. Since this thing got more popular than I imagined, I made V3 to save everyone some filament. V3 has the lower and upper housing split higher so it requires a lot less support material.
Assembly:
To assemble, first bolt your 540 motor to the bottom of the lower housing (use thread lock compound here). Then press the rotor on to the shaft until the lower flange of the rotor is flush with the recess in the housing. Use the holes in the back of the lower housing to push up or remove the rotor if needed. Next use M3 bolts to fix the upper housing to the lower housing.
If you have a motor with suitable startup torque, you can get the fit between the upper housing and rotor much tighter to where they actually make intermittent contact while rotating. If the fit is just right, when you start the motor the first time, the rotor will machine itself to the shape of the upper housing, providing a very small clearance for even more pressure. Note that if you use this "wear in" method of fitting, you have to use a more workable filament for the rotor, like ABS. More brittle filaments may snap off a rotor vane in the process.
Notes:
I made the design so I can easily change aero parameters and quickly generate new STL files. So if someone needs say, less clearance, more intake or exit area, a different mating tube, etc... just let me know. In the process of drawing this thing, I imagined experimenting with printed electric motor powered compressors could turn into another side hobby, with lots of rabbit holes to explore. I hope that sharing this leads to development in printed compressors, and some neat improvements to this and other designs. Maybe eventually we will be able to print a screw compressor, or even a conical screw! ;)
Lastly, 1+psi does not sound like much, but it is a lot more than the typical commercially available inflatable blower (these typically get to ~0.5psi). So please be careful using this... for example don't leave it alone to fill up a pool toy, as it could burst!
Updates/Revisions
1- I uploaded "V2" stl files that I am currently experimenting with. V2 adds some changes to the volute geometry that should slightly improve performance. V2 also comes in 2 sizes, one with a 36mm diameter inlet (like the original), and one with a 42mm inlet. The lower housing works with all rotors and uppers.
2- I uploaded some "V3" stl's for the 42mm version, which work with the 42mm rotor. V3 brings some ease of printing changes as promised earlier. The aerodynamics are otherwise identical between V2 and V3.