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!

Views: 3720

Comment by Eli Cohen on January 14, 2015 at 5:07pm

wow, this looks awesome!

I have a matlab script I worked on last year to model motors and propellers (using blade element theory and a simple electrical model) and compare the output to published data. We ran some wind tunnel tests but we were missing torque and it was a huge pain. This looks great and I would be happy to contribute what I have to building more...

Comment by Charles Blouin on January 14, 2015 at 5:47pm

@Eli I understand, I think universities would use this a lot! My friend completed his masters and I am finishing mine. That kind of device would have been useful. It is possible to buy a torque meter for small motors (I looked), but they are tens of thousands of dollars.

Comment by Eli Cohen on January 14, 2015 at 5:58pm

on our setup, we have 3 force sensors under our test platform. one each to the left and right of the motor and one is about a foot behind it. by taking the difference between the left and right ones and multiplying by the lever arm, we get torque but the sensors take a really long time to settle.

are you running off a constant voltage power supply for these tests?

Comment by Doug Walmsley on January 14, 2015 at 6:17pm

My interest is with coaxial airframes. How does your rig work with this type of configuration?

Comment by Charles Blouin on January 14, 2015 at 9:02pm

@Eli: We use a power supply for obtain a constant voltage. I suppose that if people were using batteries, the thrust and torque data could be ''normalised'' to a standard voltage if we were to make a database.

@Doug: You could mount the coaxial on the test base directly, but it would need a custom attachment (which could be as simple as double sided tape). We are currently attaching our air frame directly to the base.

Comment by F1P on January 14, 2015 at 10:50pm

Interesting experiment!
But i think there is need one more valuable axis - Voltage =)

Comment by Tiziano Fiorenzani on January 14, 2015 at 11:28pm

Replied to the survey. Good luck, i'll buy one

Comment by Hugues on January 14, 2015 at 11:33pm

Interesting. A question: in your graph above "efficiency map for blade T" title states a max efficiency for values that are out of the graph. Bug or misunderstanding?

Comment by Adam Kroll on January 15, 2015 at 2:31am

What are the z scales ie colours referring to in both graphs? This project would be really worthwhile for developing aircraft for endurance.

Comment by Bart Theys on January 15, 2015 at 2:48am

That's very interesting! Especially since you got it all automated. I also built a test-setup and make the torque measurements with a leverage arm on a pivoting attachment point for the motor. I use different propellers on a motor/esc combination to measure the efficiency:
This graph could also be plotted as a function of RPM and Torque, but pwm and current are easier to measure for mostly. I concluded from this graph that ESC's lose efficiency at low pwm ( throttle setting ) which makes sense.


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