Build Guide: Calibration

Calibration and Adjustment

 After logging in, choosing to skip login, or first thing when loading MinumOS for subsequent sessions, you will be prompted to calibrate the sensor to the screen by touching and holding an orange crosshair in each corner as you are prompted.

calibration screen showing upper left crosshair point

Shown above is the first of these, the upper left corner, and as you touch and hold each one you will see the next one appear.  This step basically tells the system what the projected dimensions and alignment of the projector is compared to your sensor frame.  This makes it so that you do not have to have the projector aligned exactly with the sensor or even have it aligned the same way every time.  

If you are just trying out the software on your computer, not yet using a projector, you can just simply click on or touch (if using a touchscreen) each of the crosshairs as they appear (or skip it using the skip button to use your screen's dimensions).  If you are using the full projector setup though, there are a few tips to make sure you are getting the best results:

  • Remember that the sensor is not right up against the screen - it is sitting a distance away.  Wherever you cross the sensor, regardless of where you actually impact the screen, is where the system will sense your touch. 
  • I recommend using an arrow with a blunt on it for the calibration.  While sighting down the arrow, line it up with the crosshair on the screen and then hold it straight until the on screen directions prompt you to move on the next point.  Do not move it until prompted (and the crosshair disappears).
  • If you aren't happy with your calibration, you can always rerun the sequence by clicking the calibration logo in the upper right corner of the main menu.  Take your time here and get it right for best results when shooting.

Now that you have calibrated the sensor to the projected image, you will be taken to the main menu where you can select a module, add shooters as required by the module, and then start shooting!

In addition to calibration, there are two key sensor settings that can help fine tune accuracy.  These are located in the global settings menu (upper right of the screen).

sensor sample time and outlier threshold settings

The first of these settings is the sensor sample time.  Because the sensor was not designed to sense such fast moving objects, the software samples all readings of the sensor in a time window.  During this time it stores coordinates that it reads, and then this brings us to the second setting.  It then uses the earliest coordinate from the sample collection that is within the outlier threshold from the rest of the samples and so effectively throws out any erratic reads from the sensor.

Finding the optimal values for these settings can take a bit of trial and error since it will vary according to your computer, sensor, and arrow speed.  However, if you find that you are getting erratic reads from the sensor, increase the sample time or decrease the outlier threshold.  On the flip side, if you find that the sensor reads low, picking up the arrow as it is falling, decrease the sample time or increase the outlier threshold.

Lastly, there is one other adjustment that can help fine tune the hardware that will require a bit of trial and error.  By moving the sensor closer to or farther from the screen, we can find the perfect balance between reliability and accuracy.  Without the backstop, arrows often fly faster than the sensor is capable of registering.  However, with the backstop stopping the arrows while part of the arrow is still inside the sensor, we are giving the system much more time for it to register a shot.  By moving the sensor farther away from the screen, the sensor has more time with the arrow inside of it, increasing the reliability of registering.

On the other hand, the farther away the sensor is from the screen, the less accurate it may be if the arrow is shot through the sensor at a more extreme angle.  It is possible to pass through the sensor aligned in a way that your actual impact on the screen differs.  Thus by moving the sensor closer to the screen, we are decreasing the effects of this angled shot issue and so it becomes more accurate.

Hardware rig sensor distance adjustment
You can adjust the sensor by loosening the T connectors that can then slide on the foot long conduit pieces that suspend the sensor in front of the screen.  Sliding these back and forth allows you to move the sensor closer to or farther from the projected image on the screen.

I recommend starting with it as far as it will go from the screen and then as you test more, periodically move it closer.  If you start to see shots not register, move the sensor back away from the screen a bit and it should be in the optimal spot.

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