Converting period to Miles Per Hour

[SFOdesigns]

http://sfodesigns.com/aboutsfodesigns.html

that could match the question ... and create some ...

Alain

Hi,

as always, I'm either giving too much information, or not enough....

This is the rear wheel of a motorcycle. The bolts, 5 in all, mount the rear pulley (belt drive) to the wheel. The circumference I provided is an actual measurement with the rider mounted. I realize that tire pressure, load, and temperature all have an effect on circumference, but i'm not that worried.

The speed can reach 100 mph in actual riding.

Thanks,

Roy

[Acetronics2]

Hi,

as always, I'm either giving too much information, or not enough....

This is the rear wheel of a motorcycle. The bolts, 5 in all, mount the rear pulley (belt drive) to the wheel. The circumference I provided is an actual measurement with the rider mounted. I realize that tire pressure, load, and temperature all have an effect on circumference, but i'm not that worried.

The speed can reach 100 mph in actual riding.

Thanks,

Roy

mhhhhh ...

belt driven ??? ...

or it's one of these awful Harleys ... or it's a real vintage lovely one ! ( a steam powered one ??? )

100mph ... a bit over 40k pulses an hour

11, ... Hertz @ Maximum ... then, the pulse duration method is to use.
i'd use some soft dividers switching for the basetime choice vs speed.

the 46K22's Timer 0 looks fine for that purpose ...

But do not ask too much to a Kawa H1 owner ( yesss ... the 3 smoking cylinders !!! ) to do for a ... Harley ...

Alain

[Amoque]

I think Alain has digressed to thoughts of wind in his hair and horsepower under his seat... "Write when you find work!" - is an old expression used by my instructors to recall attention when a student's mind drifted away.

More to your concern, Roy: I think that you will want to pick a sample time that yields results near full scale as at high rotations per hour (RPH), small errors will compound quickly. Perhaps you will consider changing the calculation period over different speed ranges as 0 - 10 MPH, 11 - 25, 25 - 50, 50+ (or some such) so that your results don't follow Alain down the path to fantasy .

Oh, belatedly I see this is Alain's suggestion as well. At least he has not yet disappeared over the horizon.

[Acetronics2]

Oh, belatedly I see this is Alain's suggestion as well. At least he has not yet disappeared over the horizon.

you're a newbee here ... so, you're forgiven !!!

How sad is life without a touch of Humour ...

Alain

[Art]

Write a small program to count pulses, and give yourself a reset button,
go drive a mile. Some places have markers on the road to do this to check speedometer accuracy.
Then you will know in the real world.

[SFOdesigns]

Ok, here's my thoughts, after reviewing all of your (mostly) thoughtful replies:

First of all, I don't want to tie up my processor while a count takes place.
Second, here's what I came up with. Please poke the required number of holes in it.

My tire circumference is 78.4" and I have 5 rotor bolts. so between any two pulses, the tire travels 15.68". If I measure the time it takes to travel 15.68" and multiply it by 4040.82, I should have the mph. I divided 15.68 into 63360, which is the number of inches in a mile.

Does that make sense?

[Tobias]

One thing you might consider, look at mounting your sensor before the rear tire. You will get better resolution. Or make a reluctor wheel attached to the rear tire. For example, when I was doing data acq on race cars, it was normal to detect drive shaft rpm with a four count reluctor wheel on the driveshaft. I mounted the hall effect sensor on the housing of the rear end and counted ring gear teeth to determine drive shaft rpm. I would get 20 pulses per rev compared to 4.