Charles Blouin's Posts (11)

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10 km high flight with a 1kg quadcopter!

I was quite surprised to see a quadcopter flying that high! It was done by Денис Корякин as shown on his youtube channel.


Receiver: TrueRC 5.8GHz X²-AIR Antenna RHCP
FPV glasses: Furious True-D V3.5 Diversity Receiver System
Video transmission: Antenna FOXEER Thor 60mm RHCP / SMA PA1331
Motors: Cobra CM2206 / 1400
ESC: T-Motor f30a PC: Matek: f405-AIO
Propellers: Gemfan 7038
Battery: Assembling Li-ion 4s3p
Weight: 1.06kg

Interestingly, we can estimate the amount of energy spent to go that high and compare it to battery use. A quick estimate is 1.1kg * 10000m * 9.8m/s/s = 110 000 J (gravity energy), and 14V * 6Ah = 300 000 J (electrical energy). This is just above 30% of the maximum theoretical efficiency if there was no aerodynamic losses. The flight up was 17 minutes. You have to balance how fast you go up. Too fast and the aerodynamic losses are high. Too slow and you spend too much time hovering. For rockets, the optimal speed is about the free fall terminal velocity. That would seem to indicate that he could go higher by going a bit faster.

Another potential problem is motor overheating. I don't have much experience with motors that high, but the low air density can make cooling difficult.

Although those records are fun, there is a regulatory challenge associated with them. 10 km is about the height of airplanes, so you need clearance from ATC.

Have you flown higher?

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We are now shipping the RCbenchmark Series 1520. It measures overall efficiency, current, thrust, voltage, and motor speed. The device communicates with our open-source software, which displays and records data, and controls the motor manually or through a scripting system.


Whether you want to increase flight time for aerial photography, or performance for racing, the tool will help you obtain the data you need on your motors, propellers, ESCs, servos and batteries quickly and accurately.


A year ago, I posted here asking if people would be interested in a low cost, automated thrust stand. My colleague and I, both recent graduate from M.Sc. Mech. Eng., developed the Series 1580 dynamometer, and we obtained excellent feedback from a large number of businesses and universities. Many hobbyists asked us for a simpler, more affordable tool. We heard you, and we are now offering the Series 1520 for $165.


Get it at $149 if you order before March 1st! Additionally, for a limited time, we will refund an additional $40 if you post a video review about our tool, which will lower the product’s price to only $109. Check the product page to see if the offer is still valid.

Here are the specs:

  • Voltage (0-35 V)

  • Current (40A continuous, 50A burst)

  • Power (0-1400W)

  • Thrust (±5 kg)

  • Motor speed (100k RPM)

  • Overall efficiency (%)

  • USB interface

  • ESC manual control

  • Three servo control ports

  • Output data to CSV files

  • Real-time sensor plots

  • Automated tests and recording

  • Powerful scripting abilities

  • Safety cutoffs


We want to offer more than a test tool. You might also be interested in our ongoing video tutorial series on motor and propeller theory. For more more information, check out our website or the Series 1520 product page. I will be available here to answer questions on our tools and on motor and propeller testing.


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Estimate torque and efficiency from Kv

How do you estimate motor torque and efficiency from basic measurements? It is useful to know this information to improve flight time and performance. The video explains the fundamental relationship between Kt and Kv. It turns out you can get a lot of information from the motor Kv.

This video is part of a series. There are more tutorials on the tutorial page of our website. I transcribed the full video, so you can turn on the subtitles.

The following videos are written and will discuss experimental Kv measurement and brushless motor construction. They may take a bit more time to make because I am working on animated graphics. I think those will really help, especially to explain the relationship between Kv and motor/esc timing.

If you have any question about motors, I can answer here, and I will try to include the asnwers in the following videos.

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As promised, here is part 1 of our series on motor and propeller theory. Part 1 covers the coil magnet model, Kirchhoff's law for a motor, Back EMF, Kv, Kt, and motor efficiency.

By the end of the first video, you should really understand why is a motor is inefficient and the relation between electrical power, heat and mechanical power. The motor model is constructed part by part. I tried making this series different by giving a lot of examples while being backed by a solid theoretical background. We have more tutorials on our website. If you have any question or comment, my colleague and I will answer questions!

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Ottawa Drones Dynamometer Presentation

I was invited by OttawaDrones, a group of FPV flyers and drone designers, to do a short presentation about our dynamometer. My objective was to help them make quads and drones that fly longer and are more powerful.

I decided to do an introduction to motor and propeller theory, efficiency, and testing. I wanted to give the audience an intuitive understanding of the equations, so that they can design better, faster and more efficient quads. I tried to make this talk different and interesting by talking about the theory while giving concrete examples and showing real test results done with our tool.

Here is an overview of the talk:

  • Problem: Why test motors and propellers?
  • Stalled motor as a resistor
  • Stalled motor as an electro-magnet
  • Moving motor and back EMF
  • Mechanical power and heat losses
  • Motor timing
  • Propeller definition and parameters affecting efficiency
  • Motor and propeller selection
  • Questions

We got to demo our tool after, and we talked with really cool people! I really recommend going to one of their meetup if you have a chance. They have great projects, and you can do some indoor FPV flying in winter!

I am planning do a series of tutorials discussing more in depth each topic mentioned in the video, so your feedback and questions are very appreciated. I will do my best to answer!

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The challenge for the next five years for drones is environment awareness. Drones have been doing quite well in the lab because they have precise positioning systems. Outside, drones have to rely on SLAM, which traditionally uses heavy, expensive laser depth sensors. This is why any development of low cost depth sensors will have a big impact on the future of drones.

From MIT News:

MIT researchers have shown that by exploiting the polarization of light — the physical phenomenon behind polarized sunglasses and most 3-D movie systems — they can increase the resolution of conventional 3-D imaging devices as much as 1,000 times.

The technique could lead to high-quality 3-D cameras built into cellphones, and perhaps to the ability to snap a photo of an object and then use a 3-D printer to produce a replica.

Further out, the work could also abet the development of driverless cars.

“Today, they can miniaturize 3-D cameras to fit on cellphones,” says Achuta Kadambi, a PhD student in the MIT Media Lab and one of the system’s developers. “But they make compromises to the 3-D sensing, leading to very coarse recovery of geometry. That’s a natural application for polarization, because you can still use a low-quality sensor, and adding a polarizing filter gives you something that’s better than many machine-shop laser scanners.”

The researchers describe the new system, which they call Polarized 3D, in a paper they’re presenting at the International Conference on Computer Vision in December. Kadambi is the first author, and he’s joined by his thesis advisor, Ramesh Raskar, associate professor of media arts and sciences in the MIT Media Lab; Boxin Shi, who was a postdoc in Raskar’s group and is now a research fellow at the Rapid-Rich Object Search Lab; and Vage Taamazyan, a master’s student at the Skolkovo Institute of Science and Technology in Russia, which MIT helped found in 2011.

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Hello fellow DIYer. Last February, my collegue and I posted a survey here asking if you'd be interested in a dynamometer for drone motors and propellers. We are now releasing the production version of the dynamometer!
For the release, here is a quick introduction to motor and propeller testing, as summarized in the video above.

Why testing your motors and propellers?

You must first ask yourself, what are your, or your end user's needs? This question is important, as it will help you know what parameters to optimize for.
  • Do you want to fly longer to film uninterrupted for longer periods?
  • Do you want to carry a larger payload?
  • Do you need more thrust and power to go faster, or to improve handling in strong winds?
  • Do you have overheating problems, and your application requires you to minimize failure rate?
The final choice of power system depends not only on the airframe and payload, but also on your application.

What parameters should I measure?

The motor

NTM propdrive 35-30 brushless motor and Quantum 13-4 carbon fibre prop.

To fully characterize a motor, you need to measure the following parameters.
  • Voltage (V)
  • Current (A)
  • Throttle input (%)
  • Motor load or torque (Nm)
  • Speed (RPM)
The RCbenchmark software automatically calculates the following parameters for you:

  • Mechanical power (Watts) = Torque (Nm) * Speed (rad/s)
  • Electrical power (Watts) = Voltage (V) * Current (A)
  • Motor Efficiency = Mechanical power / Electrical power

The output speed is function of the throttle, in %, and of the load (torque in Nm). If you want to completely characterize a motor, you will need to test it with multiple input voltages and different loads. The throttle is changed with the software, and the load is changed with the type and size of propeller.

The propeller

For extracting useful propeller data, you need to measure the following parameters:
  • Speed (RPM)
  • Torque
  • Thrust
The RCbenchmark software calculates the following parameters for you:
  • Mechanical power (Watts) = Torque (Nm) * Speed (rad/s) ← same as the motor
  • Propeller efficiency (g/Watts) =  Thrust (g) / Mechanical power (Watts)

Notice that the mechanical power is the same for the motor and propeller. That is because all the motor's mechanical power output goes into the propeller, since it is directly coupled to the motor's shaft.

The overall system

The overall performance of the system depends on a well balanced combination of motor and propeller. Your system will be very inefficient if these two parts don't match well together. Because these two parts have a common link (the shaft), the overall system efficiency is calculated as:
  • System efficiency (g/Watts) = Propeller efficiency (g/Watts) * Motor Efficiency
Where the system efficiency is in grams per watts of electrical power. Changing the motor, propeller, or even switching to another ESC will all contribute to changing this calculated system efficiency.

Moreover, the efficiency value will only be valid for a specific command input and mechanical load. In practice, this means that you will test you motor over a range of command inputs, and with multiple propellers to vary the mechanical load.

How to measure those parameters?

In summary, you need to simultaneously record voltage, current, torque, thrust, and motor speed, while at the same time control the motor's throttle. By combining these readings you can extract the electrical and mechanical power, which in turn will allow you to get the efficiency values.

The RCbenchmark motor test tool was built to reduce the time and cost associated with building a custom test rig. The tool is capable of measuring all the necessary parameters while controlling the ESC, and recording the data in a CSV file for analysis.

Dynamometer Thrust load cell

Test procedure for static tests

Dynamometer test of a brushless motor and a propeller

For now, we will only cover static tests (we won't talk about dynamic tests involving angular acceleration, estimating stall torque, etc...). Before starting your tests, we recommend:

  • Installing your propeller in pusher configuration, to reduce ground effects with the motor mounting plate
  • Have a reasonable distance between the propeller and other objects, again, to avoid ground effects
  • Having all safety measures in place to protect the people in the same room
  • Configuring your dynamometer to automatically cutoff the system should any parameter exceed its safe limit
A simple but effective test consists of ramping up the throttle in small steps, and recording a sample after every step. Before taking the sample after each step, we allow the system to stabilize for few seconds.

In the video above, we manually varied the throttle from 0 to 100% in 10 steps. This procedure could also have been performed using the RCbenchmark's automatic test or scripting feature, which we will cover in another tutorial.

The results obtained are shown in this CSV file.

How to use the efficiency results?

You can summarize a lot of data points using any plotting software. Here is an example obtained using the CSV file linked above:

plot trust and propeller efficiency

You can than compare this plot with other plots generated using the same method. Try comparing two plots, all with the same parameters identical expect one element changed, for example switching propeller.

What next?

We want to publish more tutorials, with more details about certain aspects, such as automatic tests, installation, automatic kV testing and pole counting, motor theory, dynamic tests, scripting, etc. Anything in particular you would like to learn about?

If you are interested by our dynamometer, have a look here. We offer 15% off until November 15 for DIYdrones readers using the code "DIY15".

It is an exciting time for my collegue and I, as this release is the results of almost a year of work! Please comment below, I will do my best to answer your questions!
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Brushless Motor Dynamometer from RCbenchmark

RCbenchmark dynamometer website

Please comment and send feedback below. A few months ago, I posted here asking if you would be interested in a dynamometer. I received quite a lot of comments. My colleague and I had the idea of a dynamometer for brushless motor after working over one month full time on a custom motor tester for our drone. We thought that there should be a better solution available on the market. Since there wasn’t anything, we have been working full time on that project, and we are ready to release the result of many iterations and prototypes!


Our dynamometer can fully characterize propellers, and brushless inrunners and outrunners up to 40A and 3kg of thrust. The tool measures thrust, torque, voltage, current, RPM, and it has a precision ohmeter to measure the motor's coils resistance. The data is saved to a CSV file manually or continuously. Here are the technical specs:

 Voltage (0-35 V)

  • Current (0-40 A)

  • Thrust (±3 kg)

  • Torque (±1.5 Nm)

  • Rotations per minute (up to 190000 erpm)

  • Motor winding resistance (0.003 to 240 Ohm)

  • Accelerometer on PCB

See the datasheet (PDF) for more information.


Our software is open source (link to the gitlab repository), and we are actively developing it. We hope it will be hacked and improved! It has safety cut offs (reduce your chance of burning your motor), a calibration wizard, unit selection, CSV export, and much more.  If you are curious, have a look at sample results of tests made with our dynamometer here.


At the time of writing we have 14 units left available at a reduced priced for the beta period. Please join us in this project and send us feedback in the comments below!



Charles and Dominic

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Transport Canada will investigate the use of a Quadcopter for shooting fireworks. It is again people giving unmanned vehicles a bad reputation. Shooting fireworks on someone is plain stupid, I think we can agree. However, should Transport Canada be handling this case? What if they were shooting from a radio-contolled boat or car? The danger is from the fireworks, no the use of the quadcopter. Here is the report from CBC:

Transport Canada is investigating a popular online video that shows two shirtless men running on a frozen Ottawa River as a drone, mounted with Roman candles, fires exploding shells at them.

Andy Stewart, who controlled the drone in the video from the shore of a bay in west rural Ottawa, told CBC News he attached a camera to the drone so that he could record his brother and friend trying to dodge the sparks.

"We weren't doing anything to hurt anybody, just fooling around," he said. "It's hilarious how many views it's gotten."

Since it was uploaded to YouTube on March 5, it has been viewed more than one million times.

His friend, Matt Trueman, is seen lighting the Roman candles on the drone before running onto the snow-covered bay. At one point, his brother Jason Stewart is hit in the back.

"Do not try this at home," the video warns.

"We're just having fun," Stewart said. "We're not trying to hurt anybody — besides the odd, little burn. Nothing too crazy."

'Extremely dangerous' to carry fireworks on drone: Transport Canada

Transport Canada told CBC News in an email that it is "extremely dangerous" for an unmanned aerial vehicle to carry pyrotechnics or explosives.

Andy Stewart says he was 'fooling around' when he made a video of a drone, mounted with Roman candles, firing at his friends. (CBC)

"In addition, Transport Canada's safety guidelines for recreational users stipulate they should stay at least nine kilometres away from aerodrome, such as the Constance Lake water aerodrome, and from built-up areas, including homes and cottages," Transport Canada said in a statement.

Stewart said he likes making extreme videos but never imagine it would catch the attention of Transport Canada. 

"We'll see what happens (with the investigation) and take it from there," he said. "We're still going to make tons of fun videos... [we] just might not be attaching fireworks to them if it is something that you're not allowed to do."

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Drones may take advantage in more than one way of the virtual reality buzz. Valve announced its Lighthouse positional tracking solution along with the HTC Vive, and more details are emerging about the inner working of the system. You can see above the tracking station. The two inner cylinders are rotating and project a horizontal and vertical laser line across the room. The LEDs visible on the PCB are probably for the synchronization signal. 

With IR detectors on an object, is is possible to determine the position of the object using precise timing and trigonometry. Valve claims sub millimeter accuracy. The tracking station is dumb, meaning that it only projects the laser lines at a precise interval. You could add a few IR detectors on a drone and with the right interrupt based algorithm, even a 25$ Multiwii board running on the Atmega32u4 could position accurately a drone within a given space. 

For drones, it means:

  • Very low processing cost (simple trigonometry, can be done on board)
  • Unlimited number of markers and object tracked
  • Cheap hardware (consumer level prices)
  • Limited tracking (15m by 15m)

I think it is exciting news for research labs and enthusiasts. The system could provide the same level of accuracy as the $25k+ camera tracking systems. It will speed up development until full ultra precise embedded SLAM is available. I am looking forward to see the first reverse engineering post about the device protocol! Micro drones will navigate precisely inside a house.

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Motor and propeller test jig.

My friend and I are building a small direct drive helicopter. We both have a background in mechanical engineering and we found it very difficult to obtain good specs on brushless motors and propellers. Some websites provide a results database, but these databases are frequently for a combination of both motor and airplane propeller, which makes building something different very difficult. When we started rewinding motors, we built a system to measure torque, current, rpm, voltage and temperature. With torque, we can actually completely decouple the motor and propeller in the results, which really speeds up the development and allows calculating ideal gear ratios or find the correct propeller, in order to maximize efficiency.
The code is based on a modified MultiWii system with a series of connected sensors. Currently, the tests are entirely automated to test different pitch and torque combinations. There are safeguards in the code to stop the tests based on measured temperature, rpm and current. The code automatically generates graphs of the results.
That got us thinking. Would people be interested in a community-based website with motor and propeller specs? Our code is already open source and we could make our test rig available for purchase. The rig could be sold on kickstarter for approximately 150-250$ if we sell 40-100 copies. We don't expect this project to generate money really, but the goal is to help the community obtain better motor and prop tests. The system would include torque, thrust, current, voltage, rpm and temperature sensors. The instrument would include a mount for most standard motors. People with test rigs could upload the motor and propeller results on the website and specify the brand, spec or custom winding, etc.
Below are a few more images of our tests. The helicopter is a modified FBL100 and we tested quite a few motors and propellers. Our tests demonstrated that it is very difficult to make a small and efficient direct drive helicopter. It flies though.
If you are interested, please reply to this survey!
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