Digitizing a plot with 1980s technology 


Dyno charts come in a variety of formats.  Electric motors have historically been described by characteristic curves showing speed on the Y-axis and torque on the Y-axis.  This is the opposite of plots for internal combustion engines.

Back in the dark ages, I wrote a program in the C language under DOS to digitize printed dyno charts and model performance.  The digitizer was 1980s technology and pretty unreliable despite my best efforts.  I  repaired the hardware several times. 

Rather than fight with it any longer I figured somebody must have developed a method to extract that information directly from a bit-mapped image by now.   See below.

I was overjoyed to find an excellent online app that allows you to get numerical data directly from a JPG file.  It's called Plot Digitizer and is free to use online.

This caused me to transition my analysis tools to a more modern approach using spreadsheets. 

Below is an example of Plot Digitizer in action.


Although a lot of the functionality of my DOS programs is missing, the spreadsheets do allow me to display and share data with others.  (This was a primary motivation for doing this write-up.)  

Four spreadsheets are distributed across this website.  They are listed below.

Overall Ratios & Speed in Gears is not only a calculation for speed in each gear but also a convenient spot to list all the overall gear ratios for the various bikes.

Flywheel MoI Calc offers an experimental method for determining MoI as well as calculations based on material density and dimensions.

Trials Bikes Driving Force Comparison is also where all the digitized dyno charts reside.

Zero-Loss Gearbox Analysis was not needed for this evaluation but I wanted to share the tool.  As far as I know, it's an original idea.  It offers a visual comparison of two dyno charts that span different rpm ranges.  A section is devoted to using it to compare Montesa's 315R and 4RT.