Background and reason for build:
For many many years tractors have been gear driven and the Farmer/Operator would select the gear they needed by looking at the RPM to travel speed located on the dash. However, now a days, more tractor manufacturers have been offering hydrostatic drive models known as HST models. They are fantastic. They make the tractor function more like a car, giving an infinite range of speed from 0.0 to max within the L,M or H selected gear range without clutching. So basically the harder you depress the foot pedal, the more ground speed. However, there is no way to know your ground speed because one would set their RPM for the work to be done, such as running the PTO drive to operate an implement at required HP, and then control ground speed by pressure on the foot pedal. The manufacturers don't include a speedometer because every farm will use different tire and wheel sizes for their individual farm needs. They are very expensive radar speedometers that can be used, but very expensive. Even more expensive are the "mushroom tops" like John Deere's GPS systems for self driving capabilities that are typically for very large tractors. It's the utility and compact sized tractors that I am focusing on and GPS speedometer apps do not have the accuracy required for such slow speeds. Sometimes we need to know inches per minute when dragging friends and family while they're transplanting crops from a rig behind the tractor at 160 inches per minute (13.33 feet per minute).
The idea:
I have developed a speedometer for my tractor by using an encoder routed to a digital tachometer and fabricating a wheel at the exact diameter needed to cause the pulses of the encoder to match the feet per hour ground speed. The encoder wheel rolls on edge of the rear wheel's hub because mud and tire tread design prevent from simply rolling a measure wheel on the tire surface.
I would like to have a standard wheel size for the encoder routed to a digital tachometer. The Farmer/owner could divide the standard size encoder wheel by the quotient of the circumference of their rear wheel hub divided by the rolling circumference of their rear tires and this be their X value. I would like for them to be able to input and set the variable X value (determined by tractor model and tire size) and the Arduino divides the N, input pulses of the encoder, by the X value and transmits the quotient as the N to the digital tachometer.
Is this something that has already been done and/or is this something that an Arduino can do?
Thank you in advance for any input or advice.