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Here you can find out how to assemble the Bell-Boy device, what to do first once you have assembled it and how to use it.
Like many pieces of technology, it is absolutely not necessary to understand completely how it works in order to use all of its functionality. That said, some explanation will help ensure you get the best from your device. First some terminology:
- Bell-Boy device - this is the device you have constructed or which has been constructed for you. In normal use it will be affixed to the side of the headstock (when the bell is down) in line with the gudgeon pins. It does not matter which side of the headstock the device is mounted on.
- IMU - this is a small chip on the Bell-Boy device's PCB. It has three electronic gyroscopes (each measuring rotational velocities in one of the three axes) and three accelerometers (measuring acceleration - again one for each of the three axes). The IMU used in the latest version of the Bell-Boy device uses a ICM20689 IC a successor to the very popular MPU6050.
- Raspberry Pi - this is the computing device that is at the heart of the Bell-Boy. It reads samples from the IMU, puts them through a mathematical process to obtain the angle of the bell, the rate at which it is rotating and accelerating and makes these available to a webserver also running on the Pi. The server pushes data to the user's browser that does some further processing and then displays the result on the screen.
The most important thing to appreciate first is that the IMU does not measure rope pull strength. All it can measure is the rate at which the bell is rotating and the acceleration that the bell is experiencing. This means that stronger pulls on heavier bells may register as being the same as weaker pulls on lighter bells. This has the disadvantage that there is no absolute measure of pull strength(*) but has the advantage of easier comparisons of bell handling techniques between bells of different weights.
(*) Actually, absolute pull strength could be directly calculated but that would require some quite detailed measurements of the bell system.
The raw measurements taken by the IMU are used to estimate the position (angle) of the bell. This estimation uses a mathematical algorithm and works out to be pretty accurate.
The measurements also have a large gravity component that has to be removed to show something that is more analogous to rope pull strength. To give you an idea of what we are dealing with, see this image:
This image shows a few strokes of the bell overlaid on each other. The angle of the bell is on the X axis (handstroke and backstroke are both plotted but you can't see the difference here because they are on top of each other). The Y axis is the rotational acceleration of the bell (which has had a small amount of smoothing applied). The red plot is the raw reading showing all acceleration. You will see that it is mostly a sine wave which is what you would expect for gravitational pull on a rotating system. The big spike at the extreme left of the plot is a stay bounce. The little red triangles close to the axis show where a strike is detected. The blue plot shows the result after the effect of gravity has been removed. It is mostly flat apart from two bumps (which are strike related) and the far left and right of the plot which shows an accelerative effect at start of handstroke (left and above the axis) and at start of backstroke (right and below the axis). These are what is of interest here as they are primarily caused by the pull on the rope (and also the weight of the rope).
(Aside from gravity, there are other effects such as that of the clapper (whilst joined with one face of the bell and when striking), vibration, stay bounces, friction, the weight of the rope and changes in the bell-system's moment of inertia as the rope winds and unwinds on the wheel (you can even see where the rope winds and unwinds - the little dip below the axis at around 90 degrees). These are large effects but they are dwarfed by the gravitational effect. The gravitational effect is so large that the angle of the bell has to be known to a fine degree of accuracy (sub 1 degree) in order to properly remove it. The other effect that is not as large as gravity but is very significant, relates to changes in moment of inertia caused by the rope wound on the wheel. It is significant because it is at its largest just at the time the rope is being pulled to control the bell. Indeed, at backstroke where its effect is larger, it is equivalent to about half of a "normal" pull and (without adjusting for it) really masks what the ringer is doing.)
If you are interested in the technicalities behind this project, first of all may I applaud your inner geek and then may I refer you to the technicals page. I will welcome any comments for improvement (best on the issues page of this project) and would especially welcome PRs which I will review as soon as I can.
The Bell-Boy device is not that sophisticated but it uses two technologies in its communications with your browser, websockets and Javascript. You need not know what these are but the Bell-Boy device will not work with browsers that have not been updated since (about) 2012 or which do not support Javascript. The Bell-Boy device is best operated via a browser running on a computer or a laptop. It will work with many tablets but the browsers on tablets are sometimes designed to resize or zoom the page in a way that the software does not understand, so the display may not be as neat as that on a laptop. If the display on a tablet looks wrong, you can tap the settings icon (the pink cog at the bottom of the screen) and that should reset things. The Bell-Boy device will also work on mobile phones but many of the browsers on phones have Javascript disabled and you will need to go into the settings on your phone to enable Javascript.
The Bell-Boy device is not designed to be secure, it is designed to be accessible and easy to use. Anyone within range of its wifi network will be able to connect to it (it creates an open, unsecured wifi network). If there is demand, I could pretty easily insert password protection both for the wifi network (and also for the windows file share).
Have fun
BBUK