Question About Speedometer Input Signal

powert · 09-10-2007, 06:16 AM

Recently I replace my FD with one from a 2002 model. The speedometer sensor is in the FD on my 2001 and on the 2002 it was else where (transmission?). The 2002 unit did have the ABS sensor. My question is how is the signal generated? It appears that there is a chopper wheel per se in the '01 FD. Is there another method of generating this signal? My bike was originally equipped with ABS but most of the equipment has been removed. I did find the FD ABS sensor still connected and "stored" under the seat.

Any help is appreciated.

tm1100s · 09:03 AM

I don't have my notes handy, but there was a question about changing the FDs with and without ABS. I found that the signal generated by the ABS equipped bikes for the speedo was 12 times faster than the signal for the non-abs bikes. Also, the ABS signal was a relatively clean square wave where the non-ABS was somewhat less recognizable as a square wave and changed in amplitude (voltage out) with an increase in speed. Two possibilities: modify the sensor output to the system or change the speedo head (different part numbers for each system). BUT, you need to find out if the ECU does anything to either signal, this I don't know.

This information gathered with my limited knowledge of electronics and O-scope use and direct measurement from ABS and non-ABS bikes.

powert · 09-10-2007, 08:33 AM

My bike was originally an ABS (2001). The majority of those components were removed prior to my purchase. It has both sensors for the FD, the ABS and speed sensor. The FD I currently have installed only has provisions for the ABS sensor. I don't know if this helps.

tm1100s · 09-10-2007, 09:13 AM

If I'm not mistaken, the ABS sensor in the FD also doubles as the speedo sensor. The signal for the speedo is different between the ABS and non-ABS systems

jduke · 09-10-2007, 11:11 AM

On my 2001 model, it has two sensor's in the FD, ABS and speedo.
How do the newer models pickup the mph?

powert · 09-10-2007, 11:21 AM

jduke · 09-10-2007, 11:32 AM

That's exactly how my 2001 FD is. But if I'm understanding powert correctly, his FD only has the ABS pickup, so where is the speedometer getting it's info from? Is there a sensor in the transmission? Off the engine?

AntonLargiader · 09-11-2007, 04:36 AM

Quote:

Originally Posted by powert

Is there another method of generating this signal? My bike was originally equipped with ABS but most of the equipment has been removed.

No.

Bikes with iABS get their speed signal via the ABS unit. Your ABS2 bike (like non-ABS bikes) gets it from the separate speed sensor that you no longer have.

jduke · 09-11-2007, 05:02 AM

Anton, does the above only relate to S's? A friend of mine has a 2004 R1150RS and he has the old fashioned front axle mechanical pickup.

AntonLargiader · 09-11-2007, 07:58 AM

S, Cruiser and Rockster. And K12. The 'classic' Oilheads have the mechanical pickup, even on iABS bikes.

It's really about the instrument panel more than anything else. Bikes with electronic speedos and pickups with ABS2 get the speed electronically from iABS. Bikes without the pickup have mechanical speedos and continue to need the mechanical pickup with iABS.

jduke · 09-11-2007, 08:06 AM

Thanks Anton. Any idea why BMW, as high tech as they are, would switch back and forth with mechanical on some and electrical on others?

AntonLargiader · 09-11-2007, 08:19 AM

No. They successfully (after a bad start) got away from speedo cables in the mid-'80s, so what do we see on Das Neue Boxer? A freakin' speedo cable again. Not they don't work well, but I've had them break and the gearboxes break also. Plus the accuracy is crap. Meanwhile the K marched on with electronic pickup. Then all of the newer boxers got electronic speedos, but then the facelifts didn't. If you can figure it out let me know!

It was probably the same guy who designed the sidestand interlocks that let you crank the engine until the battery is flat. Yeah, THAT was an improvement.

powert · 09-11-2007, 12:15 PM

OK I understand better now. Next question is how similar are the signal produced by the sensors? Is it possible to get the signal from the ABS sensor to drive the speedo? I know it would take a mechanical interface concerning the wiring but is the voltage/frequency produced by each one similar?

AntonLargiader · 09-11-2007, 12:25 PM

Forget it. Different in several ways.

Take a look at the Touratech IMO computers, or use this as an opportunity to go full-Motec on us!