Recorded at 480 fps, the first part of the video is speeded up 16x to show real time.
Music:
"The  baddest" by Richard Smithson
Music Vine License ID CL-2018-010-95

Here's a simple setup to observe Trichel pulses. About 3kV is applied across a 2 meg resistor and planar anode and needle point cathode air gap. The gap distance is adjusted to be as close as possible without an arc/spark forming. A 2.2 k resistor on the cathode side serves as a current sensing resistor for a scope probe.

Setup Schematic:


Actual setup:


Scope shot:
V: 0.5v per division
H: 1 us per division

The setup to measure the top voltage of my Van de Graaff generator is shown
below.


The max sphere gap distance for spark breakdown was found to be 13.5 cm. Using the equations from the paper

“Peak Voltage Measurements Using Standard Sphere Gap Method”
 by Constantin Ungureanu and Lacramioara Mihaela Nemtoi

A peak voltage of about 310 kV was obtained.
This voltage is a little higher than I expected given that the dimensions of the top terminal is 8 inches wide and 5 inches tall. Supposedly the sphere gap should not exceed the sphere radius. The 13.5 cm is larger than the radius by less than a cm.
For a second method of voltage measurement as a comparison I'm thinking of trying to measure the force between the two spheres at a distance a little greater than 13.5 cm.

Recorded at 1000 fps using a Casio EX-ZR1000. The resolution at this frame rate is only 224 x 64 pixels. I had to really zoom in to get any kind of image quality. Upconverted to 720p using a video editor.

This phenomenon was first reported by A. M. Worthington in 1882.

This Blender tippe top animation displays motion at 1/33 real time. The location – rotation keyframes were generated by a 6dof tippe top simulation coded in Python.
This simulation includes:

Full 6dof equations of motion.

Stem contact dynamics.

Modified Coulomb friction.

Coefficient of restitution applied to landing force impulse.

Positive E field reading from a charged test tube


Negative E field reading from a charged PVC pipe.


Shield cover off showing from top : grounded rotating trifoil, fixed sensor trifoil, grounded top cover.  Brushless motor and optical encoder disk for motor dive and synchronous rectifier.


breadboard


Top trace: output from transimpedance amplifier. This amp converts the small ac current signal from the sensor trifoil into an ac voltage signal.
bottom trace: output from the synchronous rectifier. This amp inverts one half of the ac voltage signal to give a non zero mean signal with the mean having the same polarity as the E field. This rectified signal is then low pass filtered and output as an E field strength and polarity reading.
 
0.2 Volts per division and 20 ms per division.

Positive field


Negative field


Fair weather field reading.


One problem with using a field mill for measuring the fair weather field is calibration.

     The purpose of this experiment is to find the accelerometer location inside a phone by placing the phone on a turntable and recording the accelerometer readings while the turntable is rotating. The methods found on the internet for doing this seemed overly complicated in terms of setup geometry and location calculations. The method I present here simplify both of these by placing the middle right side of the phone against the spindle of the turntable. This position of the phone on the turntable automatically aligns the accelerometer x and y axes and at the same time places the geometric center of the phone along the x axis.
 
Photo of actual setup


Accelerometer location calculations.


There are many free apps that can record the phone's accelerometer and gyro outputs and write them to a comma separated variable (csv) text file. The app I used was Phyphox. The csv file can then be plotted and analyzed. The turntable was carefully leveled to remove large oscillations on the accelerometer outputs Ax and Ay during rotation due to a component of the gravity in the x y plane.

Accelerometer and gyro Wz data for a run of the experiment.

The run starts with the turntable stationary then the turntable is turned on and speeds up to 45 RPM. The turntable is then turned off and slows down to a stop.
The accelerometer Az output is 1 g up because the accelerometer senses gravity as an acceleration in the up direction. It's noted that the accelerometer Ax and Ay outputs show bias terms of -0.27 and 0.085 m/s^2 respectively.

Here is a different run with linear acceleration and gyro Wz data plotted.

The linear acceleration terms Ax and Ay do not show bias terms but overshoot zero as the turntable is slowing down. Linear acceleration is an estimate of the actual inertial acceleration of the IMU by removing the gravity acceleration vector from the accelerometer outputs. This requires an estimate of the phones orientation in space and then calculating the components of gravity acceleration along each of the three accelerometer axes. The accuracy of this algorithm probably varies with model of phone.
It will be shown later that for my phone ( Galaxy J7 Crown SM S767VL ), using linear acceleration gave very bad accelerometer position estimates.

   The accelerometer positions calculated using accelerometer, accelerometer minus bias and linear acceleration data did not agree so an alternative method of measuring accelerometer position was used for comparison. This other method I'm calling the “null method” and involves varying the phones position on the turntable until the Ax and Ay readings go to zero while the turntable rotates. Because the spindle is in the way for free positioning of the phone, the phone is placed on a small platform above the spindle.

The null method setup is shown here.

The remote control feature of Phyphox came in very handy for this because I could start recording data after the turntable got up to full speed. With no startup transients on the graphs the scale of the plots remained small and I could clearly see the mean of Ax and Ay getting close to null. Once null was established a felt marking pen was used to trace circles on the protective glass cover of the phone. These marked circles allow the center of rotation and hence the accelerometer position to be measured.


Here is the accelerometer minus bias null position.


Linear acceleration null position.


Table of results

  The largest difference between the calculated position and the null position was seen in the linear acceleration with 1.6 cm, accelerometer was 3 mm and accelerometer minus bias was about 2 mm. Of course these results will probably vary with the type of phone.

  I found two good images of my phone's logic board on ebay. The positioning of the logic board inside the phone was estimated from a teardown video. The rear side of the board with all six accelerometer position estimates plotted to scale are shown here.

  Only three of the positions were on the logic board and only two of those landed on a chip. The IMU chip used on my phone is a LSM6DSL. The data sheet for the LSM6DSL gives it's size as 2.5 mm by 3.0 mm by 0.8 mm. This matches the size of the chip that the accelerometer minus bias position estimates fell on. I'm fairly confident that this is the accelerometer/gyro chip. The front side of logic board is shown below with the three positions estimates that landed on the board. None of these positions landed on a chip for this side of the board.

Some initial results are shown here:

https://photos.app.goo.gl/GuKVSEsAgJjQq1Nk7
click on the google photo image when it comes up for a larger version.

  The top two figures that look like fireworks are from positive discharges and the bottom five are from negative discharges. An aluminum cigar tube was placed open end down on the plastic and a charged pie tin was brought near the cigar tube until a spark discharge occurred. The cigar tube was then removed and the plastic was dusted with baking power. The pie tin had an insulating handle and was charged with a Van de Graaff generator.

  I'm now charging a 2 nF salt water cap and discharging it through the same cigar tube placed on 2 mm thick acrylic sheet. I started grounding the cigar tube before I  pick it up and discovered that this grounding was causing a smaller second discharge of opposite polarity to the first.
 These next two photos are with out grounding the cigar tube before removal. Positive on the left and negative on the right.

https://photos.app.goo.gl/ooJa3hBvpdrTjsh19
https://photos.app.goo.gl/eET8rr1S2dCK8fmQA

This photo is with grounding the cigar tube before removal.

https://photos.app.goo.gl/5MpABG1qwAz7DJTh9


The small inner ring of the positive discharge is the second negative discharge.
The negative discharge on the right, has an inner positive discharge that is almost as large as it is. This is because positive figures are much larger than negative for the same voltage.