Mini Q

[Glenn Beer]

Is this in response to the edge margin question? My concern is that it looks like the arm cracked when shortening it, leaving little material between the hole for the clevis and the edge of the arm (edge margin). I'm concerned the the clevis pin could pull through the servo arm if there isn't sufficient material.

It’s fine. I cut it at the next hole out then rounded it off.

 

[Glenn Beer]

Wayne, you didn’t have any 6” folding props when I visited. I found these at RADICAL RC.

 

[Konrad]

Does Maytech publish a safe RPM limit for these blades?
(Read manual carefully)

I know Aeronaut has limits for their blades.

aero-naut Modellbau GmbH & Co. KG - CAMcarbon folding prop

www.aero-naut.de

 

[Wayne]

I think that is a China blade, so keep the power under 600 watts and you should be OK.

Aeronaut doesn't offer a folding blade smaller than a 7x4.

 

[Konrad]

I think that is a China blade, so keep the power under 600 watts and you should be OK.

Aeronaut doesn't offer a folding blade smaller than a 7x4.

So for the China blades is there a manual to read, or published formulas to find the rpm limit?

Way back when, Graupner had these smaller folders.
(Please note the rpm limits, also please take into account the dive)

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[Wayne]

I like this warning they give:
Never touch the rotating propeller!

All I know is I had a larger china folder on a low KV motor and it threw a blade and pulled the entire motor out of the glider..

 

[Konrad]

I've never had a thrown blade than didn't tear up the front of the model. What I hate is that I often end up with a very tail heavy ship when the motor pulls away from the leads and goes somewhere!

Unfortunately I've had a lot of thrown blades. This is why I now look for or make up my own long continuous fiber blades.

 

[Wayne]

I have not thrown one since dumping the china blades.

 

[Glenn Beer]

I’ve been planning to run the 2206 2500kv quad motor with a 3 cell battery. Doubt I’ll get anywhere neer 600 watts.

 

[Konrad]

I don't know where the 600 watt limit comes from. But the limit for the Graupner 6 inch prop is 26.6K rpm. You might have noticed that Graupner's limits are bit higher than the limit for the same size prop from Aeronaut. This is because the Graupner prop is a bit lighter. My fear with the Maytech is that they are made from black nylon only material (no added carbon fibers even micro fibers).

My concern is that based on the quality Graupner and Aeronaut props you are near or over the safe limits of the prop.
At nominal voltage: 2500KV x 3.7v x 3 cells=27.7K rpm!
Fully charged: 2500KV x 4.2v x 3 cells=31.5K rpm!

Now we know that outrunner motors have poor efficiency ratings for an electric motor, often down below 85%. While not accurate a good rule of thumb is that the RPM capacity maps pretty well to the efficiency curve. So let's derate the RPM by the efficiency and we get.
At nominal voltage: 2500KV x 3.7v x 3 cells x 0.85 % =23.5K rpm.
Fully charged: 2500KV x 4.2v x 3 cells x 0.85% =26.8K rpm!

Again these numbers are for a high quality prop and in level flight. Any kind of dive will allow the prop to spin even faster!

All the best,
Konrad
P.S.
On a 6x4 prop, 29Krpm is close to 600watts at the prop.

 

[Wayne]

In my experience around the 600 watt level prop construction becomes much more important, any defects or poor materials will start to fail around these power level. Yes, I know watts is a silly benchmark, but it is easier to understand IMHO.

 

[Konrad]

It is my experience that blade failure is directly associated with rpm as a function of the diameter. Most OEMs' also give their safety limits based on this relationship. It is also my experience that there is close to a 30% safety margin with most of these numbers. The point of ultimate failure (thrown blades) is very close to the safety limit times 1.3. With Graupner and Aeronaut one can almost be guarantied that the blade will fail at safety limit times 1.3. This is good as it means that these OEMs' have their build process well under control. This is what I define as quality.

 

[Wayne]

Agreed. I simply use watts as most people do not know their RPMs.

I like to use a motor calculator to help select my gear. Often times I end up with a motor/prop combo I would not have thought would work.

 

[Konrad]

Do they know their watts? How often have you seen a DC inductance amp meter in a guy's tool box?

Data logging ESC would make the selection much easier as we would get in flight rpm data.

Well worth the cost! Even if you like to push the number yourself.

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All the best,
Konrad

 

[Wayne]

That is what I like about the new FrSky ESCs. Real flight data. They just need to make them smaller and lighter now.

 

[Konrad]

Do these have a brake?

FrSky Neuron 80 Amp ESC

Features:Smart Port enabled and telemetry data transmission supportedTelemetry data for ESC: Voltage, Current, RPM, Power Consumption, TemperatureTelemetry data for SBEC: Output Voltage, Current.High performance 32-bit micro-processorHigh-precision current sensor ACS781KLRTR-150U-T(Resolution...

alofthobbies.com

 

[Glenn Beer]

There is a dimensional difference between the Grapuner and Maytech blades. The Maytech has 8mm thk hubs while the Graupner is 5mm.

 

[Konrad]

That may be counter productive from the added weight. Is the pin size advertized (more bearing area)? I looked at Maytech and have not been able to find a safety chart or safety formula for these props.

Here is a failed Aeronaut blade. Note that it failed at the shoulder not at the hub (pin boss). This blade failed right at the safety RPM times 1.3 safety factor. This is the classic failure point for folding blades due to over speed (rpm). Note the crisp fibers in the fracture face.

(FYI this was a 15" or 17" prop. I forget which, but I think 15").

All the best,
Konrad

 

[Diceman]

Hey all!
I finished building my slope Mini Q. With the supplied servo frames it was real easy. ??
Let’s see if I can attach some pics.

 

[Diceman]

Still yet to Maiden it. It is balanced, I just need suggested throws. Does anyone have these yet?
Jeremy