Solving the BIG PROBLEM I have with DIY Drones! (Motor Test Stand)

More information about the DIY solution here:

Parts list for the DIY solution (affiliate links):
Aliexpress:

In this video I will finally get one step closer to building my own DIY drone. Because in this episode of DIY or Buy we will be having a look at drone motor test stands and obviously build a crude DIY one as well. With such a stand you can measure at what RPM/Power your motor creates what RPM with what thrust. This information is more or less crucial when making your own DIY drone. So let's get started!

Websites which were shown/used in the video:

Thanks to Keysight for sponsoring this video.

0:00 What Drone Problem?
2:00 Intro
2:40 What do I need to measure?
4:34 Buy Option Test
5:53 Motor Test Results
7:48 DIY Option
9:57 Verdict

[greatscottlab]

I am not sure why, but when it comes to drones then I constantly make mistakes. So if you got good guides/information/parts you would like to see in the final drone video then let me know :-)

[reverse_engineered]

Low kV motors are also meant to be used with very large propellers. Tip velocity is important; you can't have a large radius propeller being spun at high RPMs or the tips will approach the sound barrier, become very unstable, and oscillate until they destroy themselves.

[niyobara]

Some handy tips to have in mind while choosing your Motors and Props:

-The Maximum tip speed of your Blades should not be more than ~0.62 Mach (0.59 Mach is the optimal max tip speed). Because at even higher speeds the blades will start to significantly compress the air in front of it which will increase drag and decrease efficiency.

-Most Motors have a similar flux density so you can compare them with the stater volume π*(r^2)*h instead of calculating the actual Torque with T = (B^2)*π*(r^2)*h/μ_0
(B^2 as the magnetic flux density and μ_0 as the magnetic permeability of the space between them)

-With two motors of the same mass and volume:
A narrow tall motor bell will have much less rotational inertia and therefore be much more responsive. However it will be much hotter.
A shorter wider motor bell will be less responsive but much cooler because it has a larger surface area on top through which the movement of the blades will push air and cool the motor windings.
A typical ratio of diameter:height would be minimal 3:1 ore 4:1 if you fly like like a madman.

-A high KV motor’s torque reduces more slowly with RPM but will require more current to produce a given torque (this can lead to the battery being the bottle neck if it is not able to provid the needed current)

-The actual current draw (as well as the required trust for a given tip speed) will be lower than on the test stand due to a phenomenon called prop deloading. If you use a higher throttle you are probably flying faster which creates headwind in the direction of your props and therefore deloads them.

-A lager angel of attack (up to ~16°), more blades as well as a larger diameter of a propeller will all increase thrust.

-A larger diameter propeller is more efficient due to disc loading. (disc loading is gross wight / thrust area ore the quads weight distribution on the covered prop area) The propeller will produce more thrust per watt

-More blades reduce prop efficiency due to the wake from preceding blades disturbing the flow

-A larger angle of attack increases prop efficiency (up to ~8°) due to Stall
The fixed angle of attack is the fixed pitch = arctan(p/π*d); p = pitch and d = diameter
Angle of attack = fixed pitch – arctan*(V_inflow/w*r)
W*r = the tip speed of the propeller
V_inflow is the inflow velocity.
~V_inflow = 1/2*(√[m*g]/[p*π*r²]); m = the mass of the vehicle, g = the gravitational acceleration, p = the density of the air and π*r² = the area of the prop

A lot on this list is not mine but from Chris Rossers channel (sorry if this seems like advertising for another channel but especially the formulas are his and not mine so I have to give him credit)

I personally found an low KV system with bigger Motors and lower Voltage (something like 4S is fine) plus two bladed props the most efficient. If you have to chose between two Motors get the bigger one and throttle lock it through the flight controller. Try to get the current draw low enough so that you can use custom lithium packs and potential double the flight time.

[Asu]

Personally, I think your approach of starting with the motor first isn't really a good idea. The proper way is to determine your needs first and then go from the most restrictive specs to the least. This is important, especially with trial-and-error approach as changing the most restrictive specs will be challenging and oftentimes means starting all over again.

When coming up with a quadcopter, I'd start with the payload first. What kind of load I'll be strapping on? What is the size and weight? You'll need bigger quadcopter with more load obviously, and the quadcopter size comes in either motor-to-motor wheelbase (450mm) or propeller diameter (9"). Generally, a quadcopter with 7" prop should handle up to 200g. I'd push up to 500g for a 9" quadcopter. There isn't any absolute guideline on this because every system performs differently, but it should give you a good approximation of what frame you should settle with.

With the suitable wheelbase picked, then comes the propulsion system. Just go with the recommended setup for that particular size and you should be good to go. For example, the 450mm frame I mentioned is optimized for a 9" to 10" propeller. Typical 9" propeller requires motor ranging in size of 2208 to 2312 to spin. For the KV, it comes down to what electrical specification you want to go with. For a 4S system, the setup requires motor in the range of 920 KV. For a 6S system, the setup requires motor in the range of 610 KV. Basically, pick the frame and propeller size. Motor size has to be enough to spin the propeller, and the KV has to be enough to give the speed for thrust generation, while not being overloaded by the propeller.

The battery can be a bit tricky, but it's very forgiving. Unless you're looking for absolute efficiency or a mission that requires the battery to last down to 10% of the charge. There's no need to calculate the most optimum battery size and you can trial-and-error it if you want to. Then, the electronics are the least restrictive here. Determine the ESC capacity by the maximum theorized current and voltage. For the previous setup, a 25 and up 6S ESC will do the job. Pick your favorite flight controller that will do the things you'll throw at, probably like GPS support or autonomous missions. The rest are pretty much up to you.

Just because you started your project since 2016 doesn't mean you have to be stuck with the technology coming from back then. The industry in quadcopter has come a long way since then, and more and more hardwares are released that are cheaper, more capable, and way easier to work with. Some of the performance motor classes have improved that it might worth forking over, while general usage motors are pretty much the same. The electronics have improved a lot in the recent years. ESCs that won't randomly kamikaze mid-flight and come with 32-bit MCU, hardware PWM, and dedicated driver that runs silent and more efficient. Flight controllers with capability to fly a quadcopter with 4 different propellers and motors easily, or even be configurable from a smartphone with standalone app. Open-source control transmission with LoRa modulation that can do 30 KM on a legal power level and 2.4 GHz frequency. HD video transmission system that can broadcast 720p image with less than a tenth of second latency and 10's KM of range.

And talking about your approach on testing the motors, there are a lot of things to consider. With the given input power and propeller combination, the two favors the smaller motor despite it won't be optimized for your purpose later. The larger motor requires larger prop to drive and will beat the smaller motor in terms of efficiency and low-speed thrust generation with optimized setup, the two you'd be looking at for the class you're the most suitable for. It's good for educational purpose, but I won't make any conclusion out of it.

Will be updating this guide later.

[engineeringhustle]

In my opinion the DIY is the winner. For building drones as a hobby there is not even a test stand needed. I built my drones without owning one. There is a ton of information out there what motors, escs and props go together dependent on your payload requirements.
I'm excited to see how your drone turns out in the end.

[FAB]

There's a lot to write here and it's 3:30am, so I don't know how much I'll fit into this comment, but I'll try ;)
-You're using very old tech! Motors, ESCs, prop design and batteries have changed a lot since 2016. I'd suggest researching a bit on the newer tech and getting something that might be better suited for what you're doing. A great channel to follow are Joshua Bardwell, which mainly focuses on 5" drones (the "standard" for acro, freestyle or racing), but a lot of that stuff translates very well to other sizes and shapes as it's all very modular and interchangeable. A GREAT resource (no pun intended) is also Oscar Liang's website. There you can find pretty much everything! Pay attention to when the articles are posted though, as he's been around for a while and some of them are pretty old! Joshua Bardwell also has a website, with broader tips and sections where it points you at what to get for your needs more directly. Great to not feel overwhelmed when you first start! Much of the stuff I write here is on there, probably written better than this, haha

-I'd suggest looking at the newer ESCs, as those are the things that have changed the most, with different protocols and firmware that allows you to really customize them in depth. Especially the ones with BLheli32, they have 32 bit controllers and are extremely customizeable.

-As for props, efficiency isn't the only parameter at play: less blades are usually more efficient, but more blades are more responsive and generally have better flying characteristics and fewer vibrations. It's a similar thing with the size, bigger is way more efficient, faster and it can carry more weight but it obviously gets heavier and less maneuverable, while smaller is more "zippy" but with lower flight times and it's slower. It all depends on what you want to do with it, and as somebody suggested here I'd say that the first and most important thing you should do is figure out your needs: long range? Acrobatics? Carrying stuff around? Close range fast fun? Hyperfocused racing around a "circuit"? Cinematic shots? All valid uses, and all with different quirks and different design choices!
As I mentioned before, 5" (prop diameter) is kinda the "standard" for most hobbyists. It's in quotes because there really is no standard and you're free to choose what to do, but you're really gonna find the most documentation and parts for 5" drones with three bladed props. The knowledge is generally scalable (unless you go really small or very big) but if you wanna go the "easy" route for a first build there's that. It's 5" because it's kind of a sweet spot between battery life, speed, maneuverability, and ease of building them. Then if you go more specific you will want to change stuff up! Want more range and don't plan on doing stunts? 6 or 7", with 3 or 2 blades is good. Want a very light drone that people aren't gonna be scared of, that will suffer a bit from wind and will have a worse battery life? A "toothpick", 3", 3.5" or 4" is for you. The other advantage is that they're also easier to keep under 250g to have less trouble here in the EU. Batteries are also cheaper to buy so the low battery life is less of a concern. Just buy more batteries! ;)

-batteries! Here the "standard" for 4", 5", up to 7" or slightly more (I'm not experienced with stuff bigger than 7", so don't quote me on that) is 4S or 6S, with 6S being the preferred one at the moment as it allows motors to be more efficient and more responsive. It's mainly for acro though, so if you're just cruising around 4S is generally cheaper. 3-4" generally are 3S or 4S, with some 4" using 6S but IMO they're extremely overpowered. "Toothpicks" and "tinywhoops" (I don't immediately recall the prop sizes, but they're the smaller ones) usually use 1 or 2S.
The battery sizes obviously change depending on size. Tinywhoops have 450-550mAh 1S or 300-400mAh 2S batteries, 3-4" I'm not sure as I don't own any (IIRC about 800mAh 4S), 5" use around 1500mAh 4S or 1100-1200mAh 6S (they generally stay at around 22Wh), and so on.

-motors, this is another can of worms! Generally the community has already figured out the ideal sizes and KV for each prop diameter/cell voltage combo. You generally want a taller, thinner motor for more performance and responsiveness but a wider, shorter motor if you want to carry weight and need the motor to have better cooling. I'm most experienced with 5" (as you might have understood), there the most common motors are 2306 or 2207 (referencing the dimensions in mm of the stator, xxyy where xx is width and yy height). It generally doesn't make much difference at all if you're not extremely experienced, but other prop sizes might have a wider range of measures, you can reference the community or other people with more experience than me in those prop sizes under here ;)
As for KV, your "acceptable range" doesn't only vary with battery voltage but also with prop diameter and prop pitch! What's important is the tip speed, you don't want it to go over the speed of sound and even if you're under it you don't want to stress the prop so much that the plastic flattens, essentially giving you a 0 pitch prop. You'll hear it as a as the motor suddenly doesn't have any load on it and spins up if it happens, and you'll momentarily lose your power until you lower the throttle
Besides that, you don't want to overload the motors. So, higher KV goes with lower pitch, smaller props, or lower voltage batteries, and lower KV goes with higher pitch props, bigger props or higher voltages.
Again for 5", at 4S you're looking for a motor with a 2300-2800KV, and for 6S a 1500-1900KV. For both, I'd shoot for something in the middle as it can work with most props. Choosing a 1900KV motor at 6S will limit you to only using very low pitch props. As I mentioned before, Oscar Liang is a great resource!
My tip on motors is to not stress too much over them. There are TONS of options, that go from extremely cheap to extremely expensive. The middle is actually pretty great. Avoid the extreme low end, as you'll really just find junk that gives you way more problems that aren't worth the euros you save! I got a motor bell fly off mid-flight lol. No idea how as the C clip and the running motor magnetic field should really keep it in place... But it happened lol. 5€ motor haha

In the end, have fun! Look at the resources, decide the drone's purpose and get at it! I'll be watching the videos ;)
It's 4:50 am now so I'll go to sleep

[BrianMartin]

Been following/watching your videos for many years now my friend. You inspire me.. I want to work on projects like you do but I lack any real workspace to do it. So I live vicariously through your videos. Thank you for every thing you do :D

[MCsCreations]

Dude, today we have 4in1 escs. One board where you solder all the motors. About efficiency, look for long range quadcopters. Dave_C has some fantastic designs!
Freestyle quads, on the other hand, fly for about 5 minutes at most, because it's all about the acrobatics, so it needs a lot of power.
Racers, in the other hand, are all about the lightest and more powerful possible... And there are races in Germany, so look for one of those events!
Anyway, I'm definitely looking forward to see what you're going to end up building! 😃
Stay safe and creative there! 🖖😊

[kietpham]

Hi Scott! FPV pilot here: some suggestions I would have are to use a motor from a more reliable brand (Lumenier, T-motor, RCinpower, EMAX, and some others), I'd suggest propellers that are perfectly balanced as it can interfere with your onboard gyro from all the vibrations, making more filtering needed, and more phase delay. Some brands of propellers I suggest for big quads are from HQProp, their 10x5x3s are good, they also have 9x5x3 and 8x5x2s. Master Airscrew also makes great propellers for the 8-13" diameter range. I'd also suggest using a flight controller firmware like iNAV for it's autonomy features and a lot of community support (although I'm extremely biased on that 😂). Using a newer firmware with a newer ESC (like a 4-in-1 ESC) would give you the ability to use an ESC communication protocol like DSHOT. Some newer flight controller firmwares like iNAV, Betaflight, and emuflight are capable of bidirectional dSHOT, which allows your ESC to report back RPM and more data to the flight controller, allowing you to use RPM filtering. RPM filtering allows the FC to smartly target the specific noise frequencies the motors are generating.

I'm however, a FPV pilot and I build fast racing quads, and occasionally big 10" racing quads. I understand some of these might now apply to you because it seems like you want a more efficient slow flying build. But hey, anything helps!

[cullenchase]

This has probably been said, but the propellor you use makes a HUGE difference too, low kv motors spinning a large prop are generally the most efficient, larger props can spin slower for the same amount of thrust which creates less turbulence so it's a lot less wasted energy.

The lower the number of blades also has an impact on efficiency, ideally a single blade with a weight is optimal, but it's not a huge performance difference from just two blades, but going from two to three blades makes a large difference

[RecursionLabs]

Great video. I've spent a ton of time doing automated motor/propeller testing (post some results on my channel) and the biggest problem with most methods using thrust stands is controlling static thrust testing variables. The biggest two are input voltage and heat. If you can eliminate those variables, I've found you can get extremely accurate repetitive test results which is great for comparative testing. All you need to do is use a high current output bench supply and burst motors for short periods to test at each point allowing them to cool down before hand (ramping will cause them to quickly heat up and sag the voltage/thrust output). With your thrust stand you can accomplish this with some automation and get a ton of samples over a few hours. Feel free to reach out if you want to get more information.

[v]

Scott, I absolutely love you and your brain.

You keep making electronics easy to understand. It's given me tons of inspiration for a particular project I've had in mind since I was a child, and now I think I can pull it off, even if it's not as "Sci Fi" as id like it to be. Thank you!

[TechReview]

Great video! I usually do get the correct power rating, as I only choose motors with thrust documentation. Usually, I go for a 4:1 power ratio.

[JonathanDeWitt]

This is exciting to see you plan to do a DIY drone. I'm looking forward to seeing it!

[SvendsenWorks]

DIY is the winner... It can take a lot of work/time/money to get it just right, but when you get it just GOOD!

[eprohoda]

How’s everyting going?~ GreatScott!-Yeah~ best job~

[wiebel]

I love how you have the max voltage in mind for future selection of components, thus giving 1S 4.2V instead of the standard rating of 3.7V. Shows how much you are wanting to go for the absolute max on the cell count.

[tiporari]

There's a trade off between reaction mass, efficiency, thrust, weight, etc. You can calculate the thrust to weight ratio of a motor, propeller and power input combination. There are impractical numbers of combinations of propeller designs, materials, blade numbers, airfoil, materials, etc. Some practical testing is necessary. I've built many custom drones and I can say rarely do they work right on the first attempt. It's amazing how the flight characteristics vary based on small changes. Tuning is half the fun :)

[AlenHR]

This is nice, I just made a forged carbon drone frame. It was my first time working with compression molds so I filmed everything.
As motors go, I would recommend the IFlight Xing series. They are great motors, affordable, efficient, and have decent documentation. You can get something like 2814 for 9-12 inch props and 16/24V. Or you can go with 2806.5 for 7-9 inch props and 16/24V. That gives you over 2kg of thrust per motor on 100% in both of those cases. And you can get them for like 30-40 euros per motor. There are some other nice manufacturers like Diatone, BrottherHobby, etc.
They will pull 40-50 amps but with those, you can make decent cinelifter.

[Harani]

I strapped my motor to a weight and put the whole thing on some scales
I measured the weight of the whole assembly not running, and then running at various speeds 25, 50, 75 and 100 %

By subtracting the various results from the "at rest" weight, I could figure the lifting capacity of various prop/motor/ ESC combos without the need for an expensive testing stand