Introduction: How to Test the Thrust of Propellers

For most newbies or to-be hobbyists of drone/aircraft model, propellers are prone to break in plane crashes. So, how to pick or choose the right props would be quite important. But, also not that easy for green hands.

Well, actually there are some tips in selecting the most suitable props (yes, there's no definitely perfect props!!) for your aircrafts.

First you need to know, what's your preferred effect? Steady, agile, or crazy flight?

Thrust of the prop depends on: 1) size; 2) shape/surface area; 3) number of blades; 4) materials

Also take into account the diagonal motors distance, motor power, etc. when choosing.

So if you want higher power, you can use longer props like 6-inch ones, but the agility would be sacrificed. For example, to install an FPV camera on, you need the power. How the prop looks like will also determine its thrust - in the shape of bull nose (BN), hybrid BN (HBN), and pointy nose. Thrust: HBN>BN>pointy nose. Also the number of blades can affect the power: 2-blade, 3-blade, 4-blade, etc.; the more blades, the higher power.

After knowing these determinants, you may still be confused. So let the facts speak for themselves. I'll show you how to use a scale to test the thrust of props.

Step 1: Preparations

Electronic scale

3-blade CCW prop - http://bit.ly/2tAQs2x

Frame arms x 3 (to fix the motor)

SF motor - http://bit.ly/2s2hCx6

3S Li-Po battery - http://bit.ly/2t2ruLR

Radio transmitter - http://bit.ly/2sIjAoq

Receiver - http://bit.ly/2sIjAoq

Power distribution board - http://bit.ly/2s2wD27

ESC - http://bit.ly/2t1j6ww

3M tape

Wire ties

M3 screws x 4

L-shape screwdriver

Prop removal wrench

Step 2: Power on the Scale

Usually the weighing tray can be uninstalled easily. Just gently take it away. Below, there are slots and a hollow space underneath. We'll fix the motor by tying through these slots.

Step 3: Install the Motor Onto the Frame Arm

Remove the bullet cap on the motor with the prop removal wrench.

Assemble two frame arms, align their holes to those on the motor, insert the screws into the holes, and screw them tight with the L-shape screwdriver.

Step 4: Fix the Motor Arms

Cut the 3M tape into approx. size to the arm width, stick the tape onto the arm after placing the arm onto the scale to check the sticking position. Then peel off the sheet on the tape, stick the frame arms to the scale - one directly on it, one of the combined part onto the arm already stuck, and the last arm to the other side of the scale. Fix them with wire ties - better across 4 directions centering the joint.

Step 5: Install the Prop

Place the prop onto the motor, and fix it with the bullet cap. Spin the cap tight with the wrench.

Pay attention to place the prop correctly - the motor used is a CCW one, so the prop used also rotates counterclockwise.

Step 6: Wire Devices

First thread the three wires of the ESC (electronic speed control, the other end already soldered to the section board with 2 power wires) through the hollow between the scale body and top frame, connect them with those of the motor.

Note: The connection can be done randomly now; later we'll come back to exchange if necessary.

Then plug the three-pin wire of the ESC to the first channel of the receiver (roll here; any channel is OK except throttle since it won't spring back to center automatically).

Power on the radio transmitter now. Calibrate its pairing with the receiver: pull the rudder (roll) slowly to the largest, hear a beep, pull the stick to the minimum quickly, then hear a short piece of music, and the calibration is done. Power off the transmitter.

At last, connect the power - power distribution board wire and battery wire, red to red and black to black.

Step 7: DONE!

Press the button of peeling off. Now power on the transmitter again.

Note: If the prop spins clockwise which is reversed, try to exchange any two wires of the three of the ESC to those of the motor, till the prop spin counterclockwise as it should do.

Pull the rudder stick to the top. The value measured by the scale should be a negative one. Note down the number when it reaches steady.

Change the prop you'd like to test and mark down another value. In the end, you have the data telling which one meets your needs best. So you got it!

Step 8: More Info. for Prop Choosing...

For more, refer to the blog: https://www.sunfounder.com/blog/proptest/

Comments

author
gm280 (author)2017-06-23

Back when I was deep into R/C aircraft I did something similar to see what props were the best. But I hooked up the airplane to a fish weight scale and then cranked the engine (2-cycle fuel) and then tached them out for max RPMs and seen how much pull they provided from the scale. That was pretty amazing to see the same pitch and diameter props from different manufacturers that were so different from each other. Usually the fiber-filled props were always the best. And I think that was because of their thin design and strength. They always out-pulled all the others.

Good project. Always interesting to see facts instead of talk about how good things are. Bravo sir!

author
SunFounder Maker (author)gm2802017-06-25

So you're not that into RC now..pity..

Actually due to different materials used and manufacturing process, propellers manufactured by each factory can be quite different even when the specifications are the same. Even those made by the same factory may differ slightly in thrust. In terms of materials, since carbon fiber is quite hard, it can provide greater thrust compared with other materials. Though the plane will be less agile in flight.

author
Absolutelyautomation (author)2017-06-24

Excellent measuring tool!

author

Thanks! :D

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Bio: We're an ambitious team for developing STEM education by Arduino and Raspberry Pi learning kits as well as robots and aircraft models/drones. Happy ... More »
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