Fans for RC motors

EVTodd

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Oct 17, 2007
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oofnik said:
I want to know if you would be interested in a fan for your TowerPro motor. I'm working with a friend who is an engineering student on making a cooling fan for this particular motor that will bolt on to the back.

I know I would be interested if your friend can get them made fairly soon. If it turns out he can't do it, let me know, I may go ahead and machine 2 or three of them on my cnc mill. Were you planning on having them made out of aluminum?
 
No, they will probably be some kind of plastic.
Todd, are your motor measurements the same? The OD is 63mm, shaft dia. is 8mm. Mounting holes are 10 mm from shaft center. Bell angle is 20 deg. These measurements were taken on my TowerPro motor and were used for my fan design. He can probably make them within the next several weeks. But he's not exactly the most dependable person on the face of the planet, so... hard to say for sure.

Roy - The PowerPanel is just ziptied to the handlebars on each side of the display with some foam backing in between. Hasn't gone anywhere yet. I figured it's already shrink wrapped, so I just sealed the ends with silicone and it should be fine. The CAT5 cable carries the four display leads plus the three throttle wires, so I'm using 7 of the 8 wires in there. I'm having a hard time visualizing your new mounting ideas - maybe a quick sketch would help? But it sounds like it's well-thought out.

Well I'm off to Home Depot in search of discarded A123's now! :mrgreen:
 
oofnik said:
No, they will probably be some kind of plastic.
Todd, are your motor measurements the same? The OD is 63mm, shaft dia. is 8mm. Mounting holes are 10 mm from shaft center. Bell angle is 20 deg. These measurements were taken on my TowerPro motor and were used for my fan design.

I don't have the motor in front of me but that sounds like exactly the same size. I think all the TowerPro 5330's have the same dimensions.

It actually wouldn't take me long at all to make a couple of those. The angle is a bit of a pain but I could turn it on my cnc lathe first for that. I had thought about nylon or delrin instead of aluminum but I'm a bit concerned that the bolts might pull through that kind of material or loosen easily since they are both pretty slippery. With the high rpms I don't want to take a chance of one coming off.
 
That's right, I forgot you had the same motor. :mrgreen: Yes it should be identical.

About the material, I think Matt mentioned that he made his fan on the recumbent out of delrin and I don't think he had any problems with that. Loc-tite should prevent any potential problems however. The screws have enough thickness to hold on to. Maybe Matt can chime in on this.

If you have access to your own cnc machinery, well.. by all means do it! I have a feeling my friend will run in to some problems making more than one unit as it's through his university and they're very picky about rules.

Anyway I'm going to be out of the country for the next two weeks visiting family. I'll have access to the net while I'm there so I'll keep in touch.
 
Bubba, I actually tried that on the bench before I mounted my motor, but I was unhappy with the results. I even put a shroud around it to keep the air flow directed. But no matter what I tried it seemed to create more turbulence than anything. Do you actually notice your motor running cooler with the fan?
 
You need to get the tube as tight as you can around the fan. As you noted, the fan without a tube is about worthless, because it seems to make mostly turbulence. If I do it again, I will reduce the spacing around the fan to about 1/16" and extend the tube to completely enclose the motor. In the picture you can see that there is about 1/8" clearance around the fan blades. With the direction of my motor, the fan sucks air. I extended the tube about 1/2 way up the motor to assure air flow around the outside and through the motor. There is a strong flow of air out of the tube and I do get cooling benefit. How much I can't say because I didn't record any data when I was experimenting.

I attempted to make a fan similar to what Matt did out of 1/2" pvc, but it seemed to just make turbulence. The blades and back were 1/4" thick. PVC is a lot cheaper then Delrin if you try to make your own.

Bubba

imag0002.JPG
 
I was just doing some pricing of Delrin on Mcmaster.com and you can get a foot of it for $27. (Matt, is this the kind you used? http://www.mcmaster.com/#8576k32/=20p5yh?)

Oofnik, doing some quick measurements on my motor I assume the fan you came up with is around 1/2 an inch thick or so? That would put each piece of Delrin at $1.13, give or take. That wouldn't be too bad. Of course there's probably only 2 or 3 of us that would actually need one.
 
I actually used 1/2 inch thick Delrin flat sheet. I used the CNC to cut the blade block out, then I chucked that plate into my rotary table on my 5 axis manual mill for the rest of the work.

Each blade took 45 minutes to make. That blade moves alot of air!

Matt
 
Matt, actually, what I meant was does that look like the same type of Delrin you used? I noticed they also have a glass filled version on their site.

My plan was to use the 2.5" rod, cut a 1.5" piece off with my cutoff saw then chuck it up in the lathe to cut the angle and bore the center hole. The rest would be a piece of cake on the mill. I'll have to look at the sheet prices first though.
 
I don't remember if I posted the cad file but here it is in STEP format, exported from Inventor 2010. I know Matt writes his own g-code because he's hardcore :p but I think it would be easier to work off of my design in a CAD/CAM suite to compile the g-code. I'm not too familiar with the entire CNC process but that's how I gather it generally works.
 

Attachments

  • impeller2.stp.zip
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oofink,

I tried a 2.5D design, very similar to yours, and was not happy with the performance. Matt's design must be a bit more complicated if he is using 5axis to cut it.

Bubba

IMAG0001.JPG
 
Actually, vanes with no sweep to them move more air in this application. Also, added depth and thinner fins works best. Those blades will still move air, though. :D

Matt
 
oofnik said:
Hmm, can you provide some more details about why the fans didn't work so well? It's hard to judge the depth from your picture but maybe there wasn't enough volume between the vanes to move enough air?

1/2" pvc, Blades cut 1/4" deep I think they were just making turbulence because I was not seeing any temp drop using them.

Bubba
 
I'm making a new thread about keeping our RC motors cool. Feel free to post your solutions, concerns, or whatever relating to this topic.
EVTodd and I are working out the design for a fan for the TowerPro 5330 motor. I'll post a pic of the design here again for reference:
file.php

The STEP file can be found here.

Maybe we should move the last several posts from Roy's thread to here since we kind of started hijacking it..?
 
Replacing the bearings seems to have helped dontsendbubbamail with heating problems.
 
recumpence said:
Actually, vanes with no sweep to them move more air in this application. Also, added depth and thinner fins works best. Those blades will still move air, though. :D

Matt

Does oofink's design meet your definition of no sweep or do the blades have to be perpendicular to the motor shaft?

Bubba
 
His blade could be a picture of my AXI fan blade!

A little blade angle is fine. The swept blade is more the issue. I am not an aerodynamicist, so I do not know exactly why. But, swept blades tend to mix the air more than move it unless the RPM is crazy high. Otherwise straight blades work best. Heck, if you reverse sweep the blades, teh move alot of air, but create quite a bit of drag.

Matt
 
I haven't taken my fluid mechanics class yet but I'm sure they cover some of this theory to some extent..
I just followed the design of vacuum cleaner impellers, which seem to work fairly well for their application. They all have either straight or very slightly curved vanes, and most of them are also angled. I honestly didn't look at Matt's fan until after I was done and was floored by the similarity. :p
 
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