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: 3730

Comment by Martin Bellomo on January 16, 2015 at 6:05pm

I see this the other day and O put it on my wish list.
But having it conected to a pc and graph everithing is much much better.

Comment by Dominic Robillard on January 17, 2015 at 10:40am

Hi, I am Charles's parner in this project, I will pitch in from time to time to the conversation. @Martin, thanks for sharing the trust rig. Yes it is a good deal, keep in mind it has no torque sensor and cannot decouple the motor and the propeller into two separate entities. As Brian said, we can consider the ESC, motor, and propeller, as three separate control volumes, and that given the proper sensors, can be completely separated in the results. Isolating the motor from the propeller allows one to predict what would be the best motor (from all the community data) for a specif propeller, or specific trust, even if this specific combination has not been tested.
Our plan is to allow our device to upload data to our website, which very quickly will provide usable community data. We will have quality plots of the results and a method to search based on your criteria.
In terms of the test rig we are developing, we want to use high precision 24bit analog-to-digital converters, and design a quality circuit giving consistent and calibrated results. I worked in a research institute where my duties where to design and calibrate high precision sensors.
Of course, all our source code will be open-source so anyone will be able to hack the rig for their own purposes if they want to add additional sensors, etc...
In the next weeks, we will post more details on the whole project, where you will be able to give valuable feedback on how YOU want it to be.

Comment by Dominic Robillard on January 17, 2015 at 10:56am

@ Greg, you raise an important question about the rig's design. I'd like to ask everyone's input on this: what is the most common motor/prop size you work with in your projects?

If we support powerful motors (>5kg trust) then the whole rig will be bigger, heavier, and more expensive. Also, it would reduce the ability to work with tiny motors/props due to decreased sensitivity of the sensors.  If our system has open-source code, and if 1% of people actually work with larger machinery, they could mod the rig themselves to support it. We may provide instructions on our site to do so. What do you think?

Comment by Martin Bellomo on January 17, 2015 at 11:10am

I like your project, and i´ll be waiting for more details about sensors and everithing.
It is important to keep an accesible price, because the ideal is too much people uploading information and tests. If you make an expensive rig then only na few can access it.

Comment by Greg on January 17, 2015 at 11:19am

I agree.  Build yours for small motors as they are more common. I'd be more than happy to make my own for larger setups if you provide code and build specs.

Comment by Dominic Robillard on January 17, 2015 at 11:20am

@Marin, yes you are correct, that it must be accessible, and design decisions will have to be made. But we do not want it to be cheap and a bad quality device. The hobbyking one has +-10g accuracy, which is very low. Of course we won't get 1/100g precision, but that is not necessary. In any case, we will clearly state the accuracy we end up with.

Comment by Dominic Robillard on January 17, 2015 at 11:21am

@Greg, glad you agree to the idea :)


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