Frequently Asked Questions

Thrust Stand and Dynamometer

What is the signification of the accelerometer reading?

The accelerometer reading is only intended to be used as a comparison tool between different power trains installed on the Series 1580. The chip used in an MMA8452Q. Onboard, the chip applies a high pass filter to remove the constant gravity.  A low pass filter is also applied to smooth the readings. The magnitude of the vibration is then calculated using the square root of (AccX²+AccY²+AccZ²).
The readings onboard the firmware are faster than the communication (about 50hz). The average value since the last communication is sent.

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:

  1. Go the the setup tab
  2. Under GUI settings, check “Activate Debug mode”
  3. 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.
  4. Turn the motor slowly to check that there is no false readings over a complete rotation.
  5. 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:

  1. 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.
  2. 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.
  3. 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 support@rcbenchmark.com and we can discuss how your testing methods can be adapted for a single unit.

Can I test racing car motors?

Our dynamometer is designed to characterize and measure the properties of all brushless motors. You can see an example of such motor characterization in the following images. The output power is in Watts.
ePowermPower
 When racing, the most interesting regions of operation are the high power region and the high torque region. The high power region, which should ideally be used during most of the race, can be tested by loading the motor with propellers, as you can see in the graphs attached. One advantage of loading the motor with propellers is that it can also be used to test the motor for overheating.
As a general rule, if your ESC and motor are not using a physical position sensor, propeller loading will be sufficient for your tests, as sensorless motors do not operate well in the high torque, low speed region. Propellers cannot generate high torques at low speed. The high torque, low efficiency, low speed region of the motor used in the initial phase of acceleration after a very sharp corner is best characterized with dynamic tests. Dynamic tests are done by accelerating a heavy propeller or a flywheel.  Our dynamometer was designed to perform those tests, but we have not done the tests and implementation yet.
In summary, our dynamometer and software can be used right now to precisely characterize the high power and high efficiency region of the operation of a motor. The tests for high torque, low speeds are in development, and we cannot promise that they will work as intended as the test have not been done yet.

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.

Dynamometer PCB

Do you ship to my country?

Most likely yes, if Canada Post supports it. If not, contact us and we may arrange shipping with an alternate carrier. See our shipping terms.

Can I test larger systems?

At the moment, our device supports 5 kg thrust maximum, with a maximum current of 40 A. We have plans to support larger systems in the future but we don’t have specific dates. In the meantime, it is still possible to use our product and hack our software, which is open source. You would have to also provide your own load cell, and possibly make your own I2C “addon” to support higher currents. This involves some basic electronics skills, modifying Arduino code, and modifying the JavaScript App. Although we designed the device to be modifiable, we cannot support these hacks and we cannot help you if they go wrong.

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 info@rcbenchmark.com.

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:

torque diagramThere 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.

Otus Tracker

How many trackers can be connected at the same time?

Currently, the limit is 13 trackers connected to a single computer.

Still got questions ?

Contact Us

Understand how it works

Learning Center