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Reply to "MTH Engine Gear Ratios"

Ted S posted:

Mark, I'm not sure that 0x09 has anything to do with the speed or odometer function.  The byte at 0x08 does a pretty good job by itself of describing the effective gear ratio and by extension, motor revolutions per inch, stripe count per inch, stripe count per second at a given speed, etc.

Your sample data only confirms what I already knew.  All diesels are geared the same at 10.5:1 and typically have the same size wheels. 

The formula for the approximate gear ratio is: Driving Wheel size in mm * the value of 0x08h as an 8-bit integer * 0.00552. 

I'm not sure why some diesels have 0x54 and others 0x55.  But the difference is only 1 in 84, or about 1.1 percent which is within tolerances for double-heading.   I also can't explain why the formula doesn't work out to the exact value in every case.

Ted, I'm going to spend some time considering your point about the byte at 0x08. I can modify RTC to use only that byte in the DTO and DOD calculations. I'll post my results.

The one strong point against it (at least to me) is that when the remote reads up the scale factor, it always reads up two bytes. Reading bytes out of RAM is fairly expensive in terms of bandwidth over the track. In every command that I've looked at, the remote never reads up any extra bytes. If it could work with just the byte at 0x08, it would not have read up the byte at 0x09.



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