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Discussion Starter #1
Hi guys and gals, I'm back again - I built a 900RR engined sandrail a while ago and very much enjoyed the support from this forum

I liked that engine so much I just bought a fisher fury with a 93 SC28 893

One of the annoyances I found last time (and indeed this time) is the lack of gear indicator. I can't seem to see an aftermarket one I like so figure I'll knock one up, I was thinking of two options:

1. A couple of microswitches on the gear lever - not sure how it would deal with neutral or missed gears
2. Take the approach of using rpm/speed to figure it out

I'm favouring the latter and wondered if anyone could help accelerate my learning with RPM/speed signals and gears/ratios

Thanks in advance

James
 

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Discussion Starter #2
After a bit of spreadsheet tweaking I think I have solved this, gear ratios on the fireblade are:

1 2.77
2 2.00
3 1.58
4 1.40
5 1.25
6 1.17

The primary ratio (clutch/flywheel) is 1.52

The final drive ratio on the bike was 2.8 and on the car this is 3.8

The magic formula is

Speed (MPH) = (RPM/(Gear ratio*Primary ratio*Diff ratio))*(wheel circumference in miles * 60)
Which boils down to

RPM/((Speed/0.065)*4.7728) = Gear ratio

Once you know the ratio you know the gear, time to do the Arduino side now...
 

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6 Posts
Hi guys and gals, I'm back again - I built a 900RR engined sandrail a while ago and very much enjoyed the support from this forum

I liked that engine so much I just bought a fisher fury with a 93 SC28 893

One of the annoyances I found last time (and indeed this time) is the lack of gear indicator. I can't seem to see an aftermarket one I like so figure I'll knock one up, I was thinking of two options:

1. A couple of microswitches on the gear lever - not sure how it would deal with neutral or missed gears
2. Take the approach of using rpm/speed to figure it out

I'm favouring the latter and wondered if anyone could help accelerate my learning with RPM/speed signals and gears/ratios

Thanks in advance

James
I guess no.2 will work best.
 

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171 Posts
Discussion Starter #4
Yup I went for the same, just waiting for my oscilloscope to arrive so I can check the signal before feeding it into my Arduino, code is all written now
 

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901 Posts
After a bit of spreadsheet tweaking I think I have solved this, gear ratios on the fireblade are:

1 2.77
2 2.00
3 1.58
4 1.40
5 1.25
6 1.17

The primary ratio (clutch/flywheel) is 1.52

The final drive ratio on the bike was 2.8 and on the car this is 3.8

The magic formula is

Speed (MPH) = (RPM/(Gear ratio*Primary ratio*Diff ratio))*(wheel circumference in miles * 60)
Which boils down to

RPM/((Speed/0.065)*4.7728) = Gear ratio

Once you know the ratio you know the gear, time to do the Arduino side now...
Holy sh!t. No one ever mentioned needing MENSA membership to join this site!!:grin:grin
 
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