Thrust Stand and Dynamometer
What is the signification of the accelerometer reading?
My optical RPM probe is not reading the motor speed.
First, please follow the installation guidelines provided in the software. To access the installation guideline, please click the ? sign beside the Optical RPM sensor in the Setup tab. In the Manual control tab, servo 1 should be unchecked.
Second, check that the system is reading the correct state when placed in front of the black section of your motor and in front of the reflective section. To do so, please follow those steps:
- Go the the setup tab
- Under GUI settings, check “Activate Debug mode”
- New information will appear on the left of the software. Look for Pin State Servo 1. It should display 1 in front of the black surface and 0 in front of the reflective surface.
- Turn the motor slowly to check that there is no false readings over a complete rotation.
- You can deactivate the debug mode after step 4 to increase sample rate during the tests.
Third, check the polarity of the RPM probe connection. The black wire should be aligned with the “-” row of pins on the PCB.
My motor is spinning too fast for the electrical RPM probe.
In relatively rare cases, the electrical RPM probe’s maximum RPM limit is too low for a motor. For those cases, we recommend you use our optical RPM probe, which has a limit of 100k RPM.
Can I connect multiple devices at the same time?
In some cases, you may want to use multiple units simultaneously. For instance, if you are testing dual-rotor configurations, or if you have specific project requirements. It is possible, but please take the following into account:
- Chrome will not allow you to open multiple instances of our App. You will need to run the second app using a second instance of Chrome. To achieve this, you will need to download Chrome Portable (Windows, MAC), in addition to the Chrome version you are already using. Open the portable executable and install the RCbenchmark software as per usual.
The two boards will not be synchronized and your two CSV files that you want to merge into a single file will not have the same number of samples. That will still work if instead of using sample numbers you rely on time. If you use MATLAB or equivalent post-processing software, you can merge the two files with a custom script. You can also do it manually in a spreadsheet software.
The timestamps will start at zero for both CSV files. Since it will be difficult to start them both at the exact same time, you may need to add a constant timestamp offset to one of your CSV files so that they match. The best is to ignore the timestamps completely and rely on time-insensitive variables. For example Thrust vs. RPM.
A lot of times, your testing methodology can be changed so that you do not need to use two units at the same time. If you believe you need to use the above solution, send us an email to email@example.com and we can discuss how your testing methods can be adapted for a single unit.
Can I test racing car motors?
What are the additional connectors for?
Two plugs are a precision ohmmeter to measure the motors’ internal resistance, great to check a motor for shorts, and for those rewinding motors. Most multimeters are not precise enough for measuring such low resistance.
There are also three plugs for temperature measurements (1-wire interface) and 3 I2C addon plugs. We plan to offer more sensors and functionalities in the future. Those are also great for hackers, as our software is open source!
Finally, you can also control up to three servos. It works as a servo tester, but it could also be useful for other hacks such as testing small helicopter swash plates and blades.
Do you ship to my country?
Can I test larger systems?
If you don’t want to go that route, we may be able to offer design services, or you can express your needs for larger systems support by sending us an email to firstname.lastname@example.org.
How do you measure torque?
A lot of people get confused about how we measure torque, because they do not see any mechanical connection to the shaft. The diagram below shows how the torque on the shaft, which is the same as the torque on the motor mount, is measured:
There are two load cells in the device, measuring FI and Fr. The distance between the load cells is “distance”. Using basic mechanical engineering formulas, we have this equation:
Prop Torque = Motor Torque = Motor Mount Torque = distance x (FI-Fr)/2
This setup was tested extensively, and it is very good at rejecting unwanted disturbances (parasitic torque). It is also simple to calibrate using the included calibration hardware.
Will it be accurate for airplane propellers?
Prop efficiency will not be accurate for airplane propellers, as they are designed for an incoming airflow. If you need that information, it is possible to use reference tables, or wind tunnel tests. For example, this paper has experimental and theoretical models. For static tests however, the results will be quite similar to what you would obtain with a quad hovering.
Once you choose a propeller, you know the torque and speed required. That is where the dynamometer is useful for motor selection, as it is possible to completely decouple the propeller test and motor test. If you know that you need 5000 RPM and 0.4 Nm of torque for an airplane at cruise speed, you can to a static test on the ground that will load the motor with 5000 RPM and 0.4 Nm, and obtain your motor efficiency and current.
Do you have a wireless option?
No, not at this time. If you need to have your computer further away from the device, for example for use in a wind tunnel, you can use a USB extension cable. We have tested this 15 foot cable with our product, allowing the computer to be as far as 18 feet from the device. Alternatively, you can use any remote desktop software, such as TeamViewer, to control the tool from any computer anywhere else.
How many trackers can be connected at the same time?
Currently, the limit is 13 trackers connected to a single computer.