Frequently Asked Questions

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.

32 thoughts on “Frequently Asked Questions

  1. Hi,

    I just received your Series 1520 Thrust stand and finished setting it up.

    However, I’m having trouble connecting it to the Chrome extension. When I plug in the USB cable, the 5V light on the board turns green but the extension doesn’t recognize that there is a device connected. It worked once in the beginning, but it has stopped working since.

    What can I do to fix this?

    Thanks,
    Kazu

    1. Hi Kazu,

      Your problem was fixed by email, but someone else might have the same question. If that happens, troubleshooting is the same as for an arduino board. In this case, reinstalling the FTDI drivers and rebooting fixed it.

      1. HI
        I’m having the same trouble. What can I do to fix this?

        1. Hi Clyde,

          You can send us an email at support@rcbenchmark.com. Can you answer the following questions?

          Have you tried another USB port? Does it make a connection sound when you connect the device? Assuming you are on Windows, do you see a USB Serial port under Ports in the Device manager?

          1. My software does not display the current

          2. I saw your email, I will reply there and follow up.

  2. hi
    I want to know that if you have a larger product to measure thrust around 10kg.

    1. Hi guanghuiyu. Thanks for you interest. We don’t have anything to offer right now, but a product supporting larger loads is in our medium term plan. If you need something quickly for business use, we may be able to work with you, but it would be a consulting project. If you are interested, please send us an email at info@rcbenchmark.com.

  3. I need some clarification, I was testing motors, props and esc, the esc is a BLHeli flash with the latest multi-shot firmware. Similar to a SimonK flashed esc the motors don’t spin at all. Is this a common occurence or are they setting that I have missed. Thank you in advance. Masha Allah fantastic tool guys, takes the guess work out of setting up.

    1. Hi Muhammad,

      Thanks for the feedback! We don’t support multishot currently, you will have to use the ESC in regular mode. We are planning to support OneShot, but we have no definitive timeline yet. Note that most OneShot ESC’s will also work in regular mode if the ESC setting is enabled (check your ESC instructions). If you still have issues starting your motors using our device, please send us an email to support@rcbenchmark.com and we will help you troubleshoot your issue.

      Cheers!

  4. The 1520 does not come with a calibration weight, and the details page state that the device is calibrated at the factory. I am concerned that the 1520 will drift out of calibration over time, as do almost all instrumentation. It this a legitimate concern, and is there a way to calibrate the 1520?

    Next, I am concerned about the Chrome app as my ability to use the tool is dependent on Google’s continued support of the app within their browser. Is there a standalone app on the horizon for the product? How about an all in one solution in which the thrust stand has a screen built into an adjoining platform, eliminating the need for a separate computer?

    Thanks!

    1. Hi Mr. Slayton,

      The drift that the device could experience is similar to what you would see on most scales. Scales used for commercial purposes have to be calibrated at a certain interval (usually yearly), but the long term drift should be negligible for hobby applications, unless the load cell is stressed over its safety limit (10kg overload). If you are concerned about the accuracy in the future, the software allows you to calibrate the test weight with a weight of your choice, up to 5 kg.

      The app can be installed offline without the chrome store, and you can easily find previous versions of chrome portable edition online if there is ever a problem. The software itself is open source, so you will always have access to it. This should allow many years of support. The software itself is a fork of Cleanflight.

      We considered a version independent of a computer. It would increase the cost significantly, and you would lose many useful functionalities, such as scripting. Exporting the data to a file would also be more cumbersome. Right now, if you want an independent system, I would recommend buying a low cost netbook or chromebook to use with the device.

      Cheers,

      1. Thanks so much for the reply. I ordered the 1520 yesterday and cannot wait to use it on the bench!

        1. Thanks! Don’t hesitate to contact us if you have any question. Your unit will ship very soon, we are a bit delayed due to moving. Cheers,

  5. Hello,

    My 1580 dynamometer rig is reading a negative burst current LPF (-0.05A) and so will will not allow me to run anything due to the safety cut-off being activated.

    What is burst current LPF and why could it be negative?

    Thanks,

    Michael

    1. Hi Michael,

      The problem is due to a recent update where we now allow negative currents. We now allow negative currents since a number of clients wanted to test their system as a generator (windmill). Simply change your lower current limit to about -0.1 A instead of zero and it should solve the problem. The current sensor can sometimes have a slight offset even when not reading any current. This does not affect accuracy during tests. let me know if I can be of further assistance.

      Dominic

  6. Hi,My 1580 dynamometer can’t get RPM data by electrical RPM sensor, why?

    1. It could be number of reasons such as: your specific ESC/motor combination, a faulty sensor circuitry, incorrect setup. Some low KV motors do not work well with the electrical sensor and we recommend using the optical RPM sensor. Please send us an email to support@rcbenchmark.com and we will work with you to solve your issue.

      1. Hi, thinks for your reply, the problem had solved, but electrical RPM don’t accurate when the RPM greater than 3000, do it beacuse of vibrate? And there is no specification in the packaging, can you give me a electronic edition, thank you very much! my email is fan123tao@126.com

  7. Hi,

    Does rcbenchmark sell structured parts separately ?

    1. Hi Anwar,

      Yes, we do it on a as needed basis. Please contact us at info@rcbenchmark.com with the parts you need and we can help you.

      Sincerely,

  8. I need to return my recently purchased Dyamnometer. I received the item the other day but I did not open the package. I received this past Tuesday via fedex.

    1. Hi Enrique,

      We will be able to help you. I will send you an email about this issue soon.

  9. Hi Enrique,

    Can 1580 test more than 28000RPM motor ? If the motor more than 28000RPM is there any way can test it ?

    1. Hi Billy,

      Yes. There is two solutions. You can use the optical RPM sensor, which is limited to 100k RPM. You can also email us at support@rcbenchmark.com for instructions on how to unlock higher electrical RPM limit. This solution might be unstable, so we do not recommend it.

  10. I recently bought a 1520 Thrust stand and it was working fine in Initial days, but now the system has started vibrating badly after a rpm of 50% even with the small rotors, Can you suggest what is happening?

    1. Hi Vibhumjay,

      Are the screws tightly in place? We recommend using blue Loctite to prevent the screws from becoming loose due to vibrations. If the assembly is solid, check your propeller balance. It will also greatly improve your flight performance.

      1. Screws are all tight in places, will check the propeller balance and then get back to you.
        Thanks for the reply

  11. Hello,

    I am looking into the 1580 dynamometer and I just wanted to know if there is a size limit for outrunner motors.

    Thanks.

    1. Hi Shereef,

      Yes, you can look in the datasheet. Inrunners have a maximum length of 55mm and a maximum diameter of 48mm.

  12. Hi,
    I recently bought an optic probe for my test bench but I can’t make it work :/
    I am using a 20A opto Pro ESC from Favourite coupled with a 2s lipo battery, I saw the probe has to be plugged in the Servo1 pins and should use power regulated from the ESC to get the 5V and not the 7.4V direct from the battery… do you have any idea ?

    I also have issues using the debug mode how do you test the pin ?

    Thanks in advance

    1. Hi Vincent,

      You need to power the optical probe with 5V from the ESC or a BEC. Is that what you are doing? You can use debug mode to see the state of the sensor once the sensor is connected. Can you get this to work?

      Please send us an email at support@rcbenchmark.com if you still have problems.

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