What in hell are you talking about. You can fill the conversation with a more technical language if you feel like it but you are wrong anyway. A fan is not a 2d object painted in piece of paper. If you turn it upside down you still have to respect the motor axis wick is the way it is mounted so you have to turn it 180° In whatever axis is normal to the motor axis. And in that case the fans will be looking the same way.
Yep yep, you are right. I was forgetting that I needed to do 180 on two axis to get back to the same view
I don’t quite get what you mean with that
Anyway. Not getting into efficiencies concerning blade design. This particular fans can be mounted anyway. The air flow will be determined by the motor rotation
Air flow is always out the front if it is a centrifugal fan as @jmasta observed regardless of motor rotation direction.
@krloz I got myself confused (as i said, this stuff can be a little counter intuitive sometimes) but my statement here still holds true:
Look at the pictures you posted above. The first one (with the prop pointed to the right) has to rotate ccw when observed from the left (near blades moving up) to produce airflow to the left. The second (with prop pointed left) has to rotate cw (near blades going down) to produce flow to the right.
This is because of the curvature of the blades and is the one of the basic fundamentals on how a prop works.
This conversation is meaningless if the fan is a centrifugal fan as centrifugal fans blow air radially and not axially
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And being the fan on the sk3 axial and flat bladed, as I think I can see on the video I posted (assuming I saw it right) all I said on my last post is still true. Correct? That’s why I painted straight lines on the photos
I still have a really hard time believing that they would put an axial fan inside a motor. It doesn’t make sense at all.
Axial fan: Rotation direction (cw or ccw) dictates which way the air flows. American blades are made so that when looking at them from behind, a clockwise rotation will blow air towards you. Spin it the opposite way (ccw) and it would blow air away from you but if you mount it backwards and now are looking the front of the blades, the opposite is true.
Props are designed to spin in one direction though, which is why I brought up ccw spinning props (brittish blades) on my last post. If you could simply mount it backwards and spin it in the other direction then why does aviation and even multi-rotor aircraft have mirrored props for cw or ccw rotation?
If you spin the prop backwards, yes it prduces airflow, but that airflow is extremely inefficient. It produces as much drag if not more but doesn’t blow anywhere near as the same amount of air.
If you have ever flown rc quads, think about using the same cw blade on all four motors, but mounting the ccw rotating ones backwards so that they blow air in the correct direction. The quadcopter would still be terribly unbalanced and although you might be able to hover (since the torque from drag could be similar) you will never be able to roll or pitch without diving straight into the ground as two of your props are pushing a ton more air than your other two.
I hope this helps you out understand a little better but again. I doubt this is relevant as I still think it’s a centrifugal fan, it would not make sense to mount an axial fan inside a motor without them specifically stating the direction of rotation plus the front side of the motor is sealed so the only way for the airflow to come out is through the sides. Why use an axial fan that pushes flow against a wall when you can use a centrifugal fan that pushes flow out the holes on the can?
I think this picture proves it is a centrifugal fan.
There is a very slight pitch to it which means that there might be a very slight axial flow but most of the flow si definitely radial.
In contrast, here is what an axial fan looks like.
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Because in some occasions you want the motor from one wrong spinning on one rotational direction and the other in the opposite to counter the centrifugal forces and have them both still pulling the aircraft along
By the way. I think you might have misunderstood how sk3 are built inside. The fan is not in the same plane as the holes I the front. The fan is mounted on the screws you can see in the front part of the can. So air has to be pushed along the motor axis for it to reach the front holes. And not centrifugally
Ok. As I was checking for a photo to ad to my last post I noticed some sk3 have the front holes on the front plate and some gave them on the can along the screws for the fan. So it could be that some models use axial and some centrifugal. 190kv with holes next to screws https://images.google.es/imgres?imgurl=https%3A%2F%2Fhobbyking.com%2Fmedia%2Fcatalog%2Fproduct%2Fcache%2F4%2Fimage%2F9df78eab33525d08d6e5fb8d27136e95%2Flegacy%2Fcatalog%2F18181.jpg&imgrefurl=https%3A%2F%2Fhobbyking.com%2Fes_es%2Fturnigy-aerodrive-sk3-6364-190kv-brushless-outrunner-motor.html&docid=upPnSwmk0MOFvM&tbnid=-PZuqagTFr4p8M%3A&vet=1&w=565&h=414&source=sh%2Fx%2Fim
Correct, the point that I was trying to make is that you could flip a prop and have the motor spin the opposite direction to achieve the same counteracting torque. The torque would cancel out but thrust produced would be very uneven, one would be producing much more thrust than the other. That is why they make cw and ccw props so that when you spin them in opposite directions, they cancel out the torque but also produce the same amount of thrust.
I’m pretty sure that every SK3 6374 picture I have seen has fan holes on the can.
That is a 5055, not a 6374. It probably doesn’t even have a fan in it.
neato. how does this graph work? is it actually recording while doing 50amps or extrapolating? Id think ideal might be with it being a bit less efficient at high speed because the motor would be having to force air with the blades. so the trade off being less efficient at high speed but cooler…and then maybe more efficient as the windings stay cool but at first look the less efficient might be better
What precisely do you want to know? Manufacturers usually have a dynamometer that they mount their motors to for testing. They are usually openloop (I have not seen anyone else other than myself have a close loop dynamometer). What that means is that they’ll mount a certain size prop and run up the motor to full throttle, measuring rpm, torque, current and voltage to create that graph, then they will mount a different prop to create the same graph at different conditions. This way you can map out all the properties of the motor and create a somewhat realistic model for simulation.
With a close loop dynamometer, you have a brake attached to your output shaft instead of a propeller that can command a braking torque. This way, you do not have to interpolate between curves and you can experimentally map out the whole thing in a single run
how would you use ur dyno to see which way the fan works best!? I think doing the same test run with the same motor but the fan repositioned, then comparing the energy spent would work. but it would have to be a pretty long run so the heat could have a chance to build or not build and be spun out.
Would you be open to taking some alternative printed designs we could send you?
I have a design with a theory behind it, and it has two chambers, the outer chamber has the blades like normal but the inner chamber is an empty room with a hole in the center that leads to the outer chamber, that way it would enable longer blades. made it but never went past that. could adapt it for the sk3. don’t have a pic on hand
Constant power (at the motor [a set rpm and torque]) runs for 10 minutes with a temperature probe in the stator. If the temperature rises above X then the test ends. Big blower fan to cool the motor between runs. Would be coded and automated. Measurements taken would be voltage and current draw for efficiency calculations.
I’m sorry but I cannot do these tests for you or anyone. The equipment is extremely expensive and running it is not trivial (takes hours to set up properly), my boss would kill me if I damaged anything doing non-work related stuff (and I would have to rebuild it…). We are talking about $30k or so in hardware between sensors, mounts, daq and escs.
Do you have pictures? Sounds awfully like a centrifugal fan.
My motors are 236kv wick are 5055 or 5065 I can’t remember. And they have a fan inside. I opened them a long time ago
If there is a fan, it will be centrifugal. It would be an extremely poor design choice to do so otherwise. I’m not sure why you’re so dead set in thinking it is an axial fan. As an aerospace engineer, I can tell you that this would be borderline stupid from a manufacturer and designer perspective when you don’t specify a rotation direction, and the engineering team behind hobbyking is neither.
its an awful camera but I wont talk badly bout my 300$ computer that does it all.
the blades are very thick here but doubled as mechanical parts so had to be strong.
a max temp test makes sense. trying to think of a test where the winner of a least watthours spent would show differently. running a wattmeter vs installing a thermometer. Id rather plug in a wattmeter if it would show the same results and have a set route I run, but being able to set-up a repeatedly doable route would be hard to do in the real world even with the same person accurately. and maybe these fans do almost nothing to begin with unless going fast.
Well. As an arts major here…naa kidding, industrial engineer but who cares. What I’m saying is that what i remember seeing when i opened my motors is a fan with flat blades at a slight angle in relation to the motor axis and with its holes on the base plate and the fan on the can. So not flowing absolutely centrifugal. Just that. Idk. I wasnt in charge of this design. For starters i would have chosen a different colour
I really cant tell anything fron the picture. Maybe if you had cad or a drawing or something that could explain the inside. Fan design is not easy, there is a ton of things you have to take into account. I’m sure there are plenty if books on the subject you can read.