The Shetland Attack Pony 6 (SAP6) Cave Surveying Device

Basic Use

SAP6 is operated by 2 buttons, A (nearer the laser) and B
Turn ON to take readings (this is measure mode): Press A twice in quick succession
Turn OFF: Press A twice in quick succession
Switch/toggle between menu and measure modes: Hold down B
Select a menu item: Press A
Move to next menu item: Press B
Return to main menu: cycle though menu items to BACK option
You can always double click A to turn OFF and then start again (eg if you unintentionally go into calibration mode)
To charge the SAP6, unscrew the end cap and use a USB C cable. It takes approx 2 hours for a full charge. Do not charge the device from a powerbank whilst taking readings as this may cause interference with the magnetic readings
You can use the USB C cable to access files on the SAP6 and to update software for the SAP6 (details below)

Measure Mode (to take readings)

Press A to take a reading. You will get an error if the device is not already calibrated. You can choose either a short press of A (the reading is taken just after the button is released) or a long press of A (the reading is taken after about a second, or can trigger a countdown timer which can be configured). Play with each mode and see what suits you.

If the reading is successful you will see three numbers on the screen:

compass at the top (degrees or grad)

inclination (+ or - and degrees or grad)

distance (m or feet) at the bottom

If the reading fails you will hear an error double beep and see an error message. The laser will also flash rapidly several times.

The laser stays on in measure mode. This does not require much power

Press B to cycle through previous readings. If you have enabled show extents, you will first see the horizontal and vertical extents of the current leg. You can tell which reading you are looking at by the small number at the right side of the display. Double click B to go back to the most recent reading.

If three successive readings are similar they are interpreted as a leg rather than a splay and the device will give a success beep (rising) and flash the laser twice. Similar means that, for each of the three pairwise comparisons between the three readings, the angular difference is less than 1.7 degrees and the change in distance is less than 5cm.

There is a bluetooth indicator on the top right of the screen: bt_on if connected, bt_off if not. If you lose the bluetooth connection, the device will store up to 20 readings in the RAM memory. Readings are sent automatically when the bluetooth connection is restored.

Readings can be saved to the flash drive to provide a backup. A reading taken more than 8 hours since the previous reading will be stored in a new trip file.

There is a battery level indicator on the bottom right of the screen. If you want to save power, turn off the device between stations.

Battery Life

Test results in ideal circumstances (room temperature, about 4m range to a white wall, 10 seconds between successive readings, display on):

~4500 readings taken
14 hours run time

There are some factors that affect battery consumption:

Temperature - poorer capacity with colder temperatures
Range - increased battery usage with longer legs
Cave colouration: increased battery usage with darker targets

Menu Mode (to change settings)

To navigate through the menu, press A to select an item and B to move on to the next item. Return to the main menu by cycling though menu items to the BACK option

You can directly turn on in menu mode by pressing A twice while holding down B

The menu options are:

Calibration

Sensors

You need to calibrate the sensors the first time you use the SAP6, and then again any time that you move to a location with a substantially different magnetic field strength or dip. The SAP6 will only save one calibration setting (in the config.json file) so if you recalibrate these values will be overwritten (though you can download and save your config.json file and reload it later).

Once you enter the calibration routine you will ideally take 24 readings. Press A to take each reading, and press B when all 24 are taken. You can cancel the calibration at any point by double-clicking A.

The recommended calibration routine (details below) starts with 8 readings taken in random, but well spread out, directions and then 8 accurate readings between two points, rotating the device by 45° along its long axis between each shot, then another, similar set of 8 accurate readings ideally taken at about 90° from the first set.

Don’t worry if you don’t get these readings exactly right (eg if you take one reading twice over), the algorithm will identify which readings are in the same direction and adapt accordingly. The algorithm will also allow you to take more than 24 readings before calculating the calibration

An example of a good calibration protocol would be to:

find a location well away from chunks of iron - perhaps in a wood or a cave
for readings 1-4, put the SAP6 flat with its screen uppermost on a plank propped up at ~ 45 degrees (or a rock at a similar angle), then spin the SAP6 round to take readings pointing up, pointing across left, pointing down and pointing across right of the plank. These four readings do not need to be accurate
for readings 5-8, drop the plank down to lie horizontal or find some flat ground and take readings with the SAP6 lying flat with the display up, then with the display down and the laser pointing the other direction. Then one with laser pointing up and one with the laser pointing down. These four readings do not need to be accurate
for readings 9-16, put the pointy cap of the SAP6 on a well-defined point and - carefully - take 8 readings that all accurately hit a target (this should be a second, well-defined point). Barrel roll (ie rotate around the long axis) the SAP6 by 45 degrees for each successive reading
finally, for readings 17-24, repeat readings 9-16 but with a new target. Ideally around 90° from the previous target.

When you press B after taking your 24 readings the screen will show the calibration process then it will display your calibration accuracy. For accurate readings this number should be under 0.5. You can then choose to either save this calibration to use for subsequent readings (press A) or you can discard the calibration (press B).

Laser

You shouldn’t need to calibrate the laser. However, you might if you want to measure from the front of the device or if you have replaced the end cap with something with a different length.

To calibrate the laser, place an object exactly one meter from the point on the device you want to measure from. Start the laser calibration routine and it will update the distance readings.

Info

Raw Data

The live, raw output of the sensors in x, y and z, converted to acceleration in ms^-2 and magnetic field strength in µT and the voltage of the battery. Leave this mode with a long or short press on A

Calibrated Data

The live, calibrated output of the sensors in x, y and z, converted to gravitational field in ms^-2 and magnetic field strength in µT and the field strength |V|. Leave this mode with a long or short press on A

Orientation

The live compass and inclination readings, along with the roll of the device and the current dip of the magnetic field. Leave this mode with a long or short press on A

Device

The name of your specific SAP6 as visible to bluetooth, and various version numbers. Leave this mode with a long or short press on A

Settings

Timeout

How long the device will wait from the last button click before turning off. Options to adjust this from 30 seconds to 5 minutes. Press B to cycle through options then A when you have chosen your option

Distance Units

Choose between metric and imperial (decimal feet) units for distance measurements. Press B to cycle through options then A when you have chosen your option

Angle Units

Choose between degrees and grads for angular measurements. Press B to cycle through options then A when you have chosen your option

Shot Timer

When you hold A to take a reading, the SAP6 will trigger a timer. The timer mode can be configured to a 0, 3, 5, or 10 second countdown. For settings greater than 0, the unit will beep every second until it takes the reading. If set to 0, it will take the reading after about a second while the button is still held (this is the normal behavior in firmware versions 1.0.2 and prior). Press B to cycle through options then A when you have chosen your option

Precision

The precision with which readings are displayed on the SAP6 screen. The default is 0.1 degrees for compass and inclination (eg 153.4° and +02.6°) and mm for distance (eg 5.342m ). This can be changed to display one fewer significant figure (eg 153°, +03°, 5.34m). Note that both saved trip data and bluetoothed readings will retain full precision even with this reduced precision setting. Press B to cycle through options then A when you have chosen your option

Show Extents

If set to On, then pressing B after a reading will show the horizontal distance of the leg, and also the vertical distance. This can be useful for drawing extended elevations.

Magnetic Anomaly Detection

The device records the magnetic dip and field strength during calibration. The device then detects if these change significantly when taking any subsequent readings. This would happen if the magnetic field altered, for example due to the presence of man-made artefacts such as scaffolding or local geological changes.

You can choose strict detection which detects most bad readings at the risk of getting a warning when there is nothing wrong. There is also a relaxed mode, and finally magnetic anomaly detection can be turned off. Press B to cycle through options then A when you have chosen your option

Save Readings

Whether to save all shots to the flash drive or not. Shots will be stored in the readings directory on the device. Each trip will be stored as TripXXXXX.csv, where XXXXX is the trip number. Press B to cycle through options then A when you have chosen your option

Back

Select this using A to return to the main menu or press B to continue cycling through the settings options

Bluetooth

At present the SAP6 can only be used with SexyTopo (version 1.7.0 or higher required) though you can connect to it directly using a USB C cable (see below)

Disconnect

Disconnects the SAP6 from the current bluetooth device

Forget Pairings

If you are having problems connecting to your bluetooth device try selecting this option which will clear all the recorded connections within the device so you can start again.

Updating your software and hacking

Software updates

You can update the software on the SAP6 with newer versions downloaded from GitHub (https://github.com/furbrain/STIC/releases/latest). You can check the software version currently running on your SAP6 using the Info menu under Device.

To update your software, first connect the SAP6 to a computer - it will appear as a drive called SAP6. Next download firmware.zip from the github repository, and extract all the files to the firmware directory on the SAP6. Warning - all files should be replaced at the same time as there are various dependencies across the files and the SAP6 may not work if only a single file is updated. Check that the device is working immediately after updating.

Hacking

This is an open source project - feel free to make your own devices, make adaptations and improvements. All the hardware and software designs can be found on GitHub (https://github.com/furbrain/STIC).

SAP6 uses CircuitPython. All the code to run it is available on the device itself - just plug it into a laptop using a USB C cable and you’ll see a USB drive appear.

You can change the code as you see fit. The version of CircuitPython that comes with the SAP6 has several additional libraries built into it:

mag_cal: This contains all the maths needed for calibration
rm3100: This is a device driver for the RM3100 magnetometer
laser_egismos: This is a device driver for the laser module 2 by Egismos
caveble: This module is a cave survey specific module to talk to cave surveying apps such as SexyTopo

File layout

In the top level director of the USB Drive, you may see:

firmware: Directory with the application code
fonts: Directory with the fonts used by the device
images: Directory with the images used by the device
readings: Directory with any saved trips
boot.py: The code that runs on startup, before all the other python code runs
code.py: This code simply calls run in firmware/main.py
config.json: The calibration and settings data for the device
manual.pdf: This documentation
calibration_data.json: A record of all the calibration shots you took the last time you tried to calibrate
error.log: Debug info stored here if the device crashes or encounters an error
DEBUG: If this file is present, then the device is in debug mode. You can also use debug.txt, or in fact any file with debug (any capitalisation) as the basename. You won’t see the normal battery charging screen, but you can double click A and start the main device running. You also get a serial connection on /dev/ttyACM0 or /dev/ttyUSB0 on linux or COM1 on windows, which will show debug information.

Make Your Own

You can build your own SAP6! You will need access to a 3d printer and ideally a laser cutter. You will also need to make some PCBs - you can etch these yourself or get a company to do it. Seeed and JLCPCB are some of the many companies that can do this for you.

PCB

Get the gerbers from GitHub (https://github.com/furbrain/STIC/releases/latest): download pcb.zip. That will contain the gerbers for the main board and also the button board. The traces are all pretty wide so you can mill or etch the board yourself.

See the bom.csv in pcb.zip for the list of components and where to get them

Solder the components onto the board - they are all fairly chunky so you don’t need to be a whizz at soldering. Don’t solder the display on initially, this is easier to do while attaching the board to the mount. Note the button 3-pin connector goes on the bottom of the board.

Plastic parts

From GitHub (https://github.com/furbrain/STIC/releases/latest) download hardware.zip

You will need to 3d print the following STLs:

abs\shell.stl
abs\cap.stl
abs\bezel.stl
abs\shim.stl
abs\mount.stl

The bezel and cap may be best printed upside down. You may find it easier to print the cap_with_vanes - this has some very thin tabs to help support it as it is being printed which can then be removed. Once printed, use a soldering iron to push 4 brass M3 inserts into the holes on the end of the shell. You will also need to push one into the hole in the mount.

TPU parts

Print tpu\Boot.stl in the softest TPU you can get away with.

Acrylic parts

Ideally, you should laser cut the following DXFs from 3mm clear acrylic. However, the designs are fairly simple so you may well be able to cut these by hand

acrylic\End plate.dxf
acrylic\Window.dxf

Gaskets

Rubber\Cap Washer.dxf
Rubber\Refined Gasket.dxf

You can use 1mm silicone sheet or EVA foam for these pieces. Note that EVA foam works well but permanently deforms when used so will need replacing if you ever disassemble the device. Alternatively, generous use of silicone grease can mean you don’t need these parts at all.

Making the sled

First solder everything apart from the display onto both PCBs. Note you can either use a mini-SPOX connector or JST PH-2.0 connector for the battery. Check it is the right way round for your battery connector. Attaching the battery reversed may cause permanent damage.
Put the display in it’s location on the mount and put the main pcb on top.
Screw the PCB in place using a brass M3 screw, and solder the display in place.
Attach the cable to the laser module and the PCB.
Screw the laser module in place using M2 or #2 brass screws.
Attach your battery to the board, but don’t glue it in place just yet.

Installing software

FIXME

Final Assembly

You can see a video of this process at https://www.youtube.com/watch?v=XkpvDELlksQ.

Attach the cable to the connector on the PCB
Apply some silicone grease to the bottom of the boot and place on the button PCB. Make sure that A is at the end opposite where the cable comes out
Apply some silicone grease to the “shelf” on the boot
Push the boot and PCB into the shell. Make sure A is nearest the end. The cable should be pointing into the shell
Push the shim into the shell - it should hold it firmly in place. You may need to press the shell down against a hard surface
If you have used a mini-SPOX connector for the battery, bend it about 45 degrees towards the laser
Put a blob of glue on top of the laser and put the battery on it. This step is not in the video
Connect the cable from the button to the main PCB
Push the sled into the shell, keeping the button cable out of the way
The side tabs on the sled should mate into some dents in the inner wall of the shell
Smear some silicone grease on the end of the shell, then put the gasket on
Put more grease on the gasket, and put the acrylic end plate on, and screw into place with brass M3 screws.
Put a little grease in the channel in the base of the cap, and put the cap washer in, then a little more grease on the washer
Screw the cap on - and you’re done.

You will next need to calibrate the device before you use it. If you are successful in building your own, please let me know, especially if you have any suggestions to make for this guide.