Vtrack vibration analysis tool for drones

Posted by Phil Tharp on September 22, 2015 at 11:38am

Vtrack is a high bandwidth vibration analyzer targeted at the drone developer and user. It contains a high accuracy accelerometer that detects vibration frequencies up to 15KHZ with a sample rate of 30KHZ. There is both internal SDCARD storage as well as a Bluetooth radio link that connects the Vtrack module back to a user's PC or Mac laptop.

Vtrack will help the drone user/designer detect various sources of vibrations that are beyond the pass band of the auto-pilot's IMU that can cause both flight control problems due to aliasing and structural damage/failure. From unbalanced props, to loose or failing motor mounts, to camera gimbal tuning, Vtrack can detect problems before they become failures.

Vrtrack starts shipping this month at a price of $329.00. For more information, please go to

http://flybynight.systems/products.html

Pleas feel free to post any questions.

Thanks,

Phil Tharp

Fly By Night Systems LLC

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Replies

  • Developer
    Randy September 22, 2015 at 11:34pm

    An interesting product.  Vibrations can be a real killer for multicopters and it's really important that Ready-to-Fly manufacturers and DIY-ers get the levels low for optimal performance.

    Copter-3.3 has improved vibration resistance and monitoring and the mission planner can even to FFT analysis on a log created with Copter-3.3 if the dataflash logs have been set to "Full IMU" logging (and you've got a good quality SD card in the pixhawk).

    Still, as Phil says, our maximum rate on the IMU is currently 1khz and 1.6khz (there are two IMUs) and this product may provide additional info and/or be easier to use.

    Better understanding of the vehicle's vibration levels and their cause is certainly a good thing so best of luck with the product!

    • Alex > Randy September 23, 2015 at 11:18am

      Thanks Randy,

      I think you're referring to the sampling rates there, whereas the actual bandwidths of those IMUs are even lower than that.

      Also, the correct mounting of an IMU in an autopilot has an opposite goal to the one of the VTrack: An autopilot wants to be shock mounted, which if done correctly acts as a low pass filter. That's because in order to navigate the autopilot wants to see the craft movement and not being confused by small oscillations. Conversely we designed our mount to be as rigid as possible for the best energy transfer.

      So given that a properly mounted autopilot is isolated from vibration, it won't help you to look into camera shake, loose joints or chassis fatigue. Which is what our product is designed to do (an for a number of other things, which are not strictly relevant to drones though).

      By the way, looks like our ordering system had a glitch up until now which didn't let you complete the order, but it's now fixed, the product is in stock and orders are open.

  • Darius Jack September 22, 2015 at 4:27pm

    Hi Phil,

    to study infrasounds generated by wind turbines, transmitted through the ground I use

    accelerometer enabled tablets coming with FFT software and 3-axis analysis windows (X, Y, Z).

    What comes more you need to sense rotation speed of individual motor to get rpm as an input clock (oscilloscope live chart analysis).

    Since 6 axis Gyro/accelerometer ATMega32 board can be purchased at $10

    http://www.ebay.co.uk/itm/6-Axis-Gyro-accelerometer-Control-Sensor-...

    I would expect 3-axis accelerometer kit to be offered at $30.

    Frankly speaking accelerometer sensor comes bundled with 6-axis gyro, so developers at DIYDrones can embed accelerometer sensor data into standard hardware/software,

    offering accelerometer  enable/disable configuration option at discretion.

    Ok, you can get rpm clock from log file and match it against FFT but it gets more complicated if not done real-time Live.

    Since a smartphone attached to the control station can be used either to watch live camera input or track GPS, gyro, motor speed, flight parameters and sensor data, a new layer can feature accelerometer data, rpm clock, 3-axis live charts and FFT analysis.

    All-in-one and priced extra $30-50.

    BTW

    Flying drone generates vibrations by default and vibrations are oked.

    What I study are resonant frequencies and amplitude of vibrations at resonant frequencies

    to keep motors, frame, moving parts contained against mechanical destruction.

    I would like to know opinion of developer/s at DIYDrones if one extra accelerometer sensor can be embedded into flight controller.

    darius

    manta103g@gmail.com

    • Alex > Darius Jack September 22, 2015 at 5:57pm
      Darius,

      Let me disclose first that I'm Phil's partner in Fly By Night Systems LLC.

      I think you make some interesting points but there are some misconceptions also:

      - Most accelerometers that you'll find in an autopilot or in a cell phone have a bandwidth below 1000Hz. 
        The MPU6050 that you linked is capped by its low pass filter to 260Hz. 
        VTrack has a 15000Hz bandwidth and a 30000Hz sampling rate. It is also calibrated for a flat frequency response within the operating bandwidth.
        The two instruments are hardly equivalent.

      - It's true that vibrations are commonly found in drones and generally cause no harm (besides wear on your joints). 
        There are though a few situations where they can be troublesome:
        1) If you ever try to fly a long focal length lens on a gimbal, you will find that all of a sudden vibrations are much more visible and understanding how to properly dampen them becomes more important
        2) Vibration harmonics of the prop/motor can couple into resonant modes of airframe components, and cause failure in mid air generally when the motor randomly runs at the 'right' speed.
            This doesn't often happen with off-the-shelves crafts because the problem has already been taken care for you by the manufacturer. But if you build your own rotor crafts long enough, it can happens quite a bit.

      - VTrack integrates the sensor, a radio, storage system and ADC in a slick made in the USA package, complete with a refined multiplatform spectral analysis software. 
        We think our price point is quite fair, this is a niche precision instrument, not a mass production device.

      Thanks for your interest in VTrack!
    • Phil Tharp > Darius Jack September 22, 2015 at 5:33pm

      Darius,

      Thanks for your reply.

      The highest  frequency response we have seen with the chips used in smart phones and tablets is 1KHZ and most are around 250HZ.

      The Vtrack has a frequency response of 15KHZ and a sample rate of 30KHZ. On the  Pixhawk (which we fly on all of our birds)  and on the Pixhawk 2 they use the LSM303D and the MPU-6000 parts. The LSM303D  has a frequency response  of 362HZ. The MPU-6000  has a frequency response of 260HZ  For an auto-pilot that is properly shock mounted, this lower bandwidth is fine.



      Vtrack is designed to detect much higher frequency vibrations that could affect overall system performance such as out of balance props, loose motor mounts and arms, damaged air frames etc. Another important function is aiding in the fine tuning of camera gimbals on higher end camera birds.



      Due to our relatively high frequency response and sampling rate, we can not only detect the fundamental frequency, but several of the higher order harmonics. This is important as the higher order harmonics of a vibration source can couple into the resonant frequency of one or more air frame components resulting in structural failure and loss of the aircraft. We have been there and done that several times....



      The user software for Vtrack presents acquired data as a spectral display with user select-able window length and frequency binning to aid the user in tracking down the source of the problem.



      We provide both a 25mm boom mounting clamp as well as a standard 1/4-20 screw terminal. With the clamp you can mount Vtrack on an arm of a multi-rotor and with the 1/4-20 terminal on just about any camera mount. Of course, you can also make any other mount you would like that attaches to a 1/4-20 terminal.

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