Engine and wheel speed drop down above certain values

Megablade
Posts: 6
Joined: Sat May 19, 2012 8:30 am
Location: Stuttgart/Germany

Engine and wheel speed drop down above certain values

Postby Megablade » Tue Apr 01, 2014 11:53 am

Hello everybody,

I've got some issues with my Dash 2: It is installed in a Westfield kitcar (Super Seven) with Honda CBR1000RR bike engine.

The motor speed drops down to zero over 8.000rpm. The same with the speedometer: Above 70km/h the gauge drops down. Both issues are reproducable with different engines and ECUs (Megasquirt and stock Honda) and also with different speed-sensors at differing positions (wheel and propshaft). All other sensors (oil/water temperature, AFR, fuel) work without any problems.

Therefore I fear that it is about a hardware failure of the Dash. Does anyone know the phenomenon? Maybe there's a problem with the wiring after all?!

Thanks a lot in advance!

Regards from Germany
Dominik

osborni
Posts: 497
Joined: Fri Dec 07, 2007 9:08 pm
Location: USA, Michigan

Postby osborni » Tue Apr 01, 2014 12:09 pm

Are you using hall effect sensors? If the iron passes the sensor too fast it might not read. My wheel speed sensors fail above ~110 mph or so. I simply need to install a bigger ferrous target for the sensor.
BMW 2000 M Coupe

Support
Posts: 365
Joined: Mon Nov 21, 2005 4:09 pm

Postby Support » Tue Apr 01, 2014 2:47 pm

Yes, this will be the problem. The pulses are not long enough and over a certain speed they are too short to trigger the input. It isn't the number of pulses which is your issue but the length of the pulses.

Martin
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Posted by Race Technology Support

Megablade
Posts: 6
Joined: Sat May 19, 2012 8:30 am
Location: Stuttgart/Germany

Postby Megablade » Tue Apr 01, 2014 6:46 pm

Hello,

below I attached two pictures of my installation (the iron is welded to the brake disc :lol: ). The radius of the sensor is ~75mm and the iron has a width of about 10mm. So at 70km/h the calculated time over the iron is only 1,8ms. Not really long :shock:

What pulse lenght is necessary to switch reliably? Respectively which width should I chose? If 1,8ms is borderline I would need 45-50mm to reach 2,5ms at 220km/h. Uffff, that's a lot! But would this be the direction to go for?

Regards
Dominik

P.S.: That's the technical datasheet of my sensor Cherry GS100102

Image

Image

Support
Posts: 365
Joined: Mon Nov 21, 2005 4:09 pm

Postby Support » Wed Apr 02, 2014 7:45 am

Think about what the maximum speed you require is, and look at the ratio of the speed it works up to and the speed you need. If it currently works up to 70kph but you need 210kph then it needs to be three times as wide. That is the simplest way to work it out.

Martin
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Posted by Race Technology Support

Megablade
Posts: 6
Joined: Sat May 19, 2012 8:30 am
Location: Stuttgart/Germany

Postby Megablade » Wed Apr 02, 2014 8:10 am

Hi Martin,

thank you, that's how I claculated. Since I want to have a little "safety buffer" I think I will go for 40-45mm.

Regards
Dominik

Turby
Posts: 296
Joined: Thu Nov 17, 2005 2:28 pm

Postby Turby » Wed Apr 02, 2014 3:28 pm

I use exactly the same sensor for my wheel speed BUT a) I use teh back of the wheel studs instead of a bit welded to the disc (stud is around 20mm diameter) and b) the sensor interfaces directly into a Motec M4 ecu. Works fine up to 210 kmh.

Do you have a pull up resistor between +5v and wheel speed output ?

According to http://www.race-technology.com/wiki/ind ... WheelSpeed 1ms is enough for pulse detection for rpm input or 0.5ms for frequency input.

osborni
Posts: 497
Joined: Fri Dec 07, 2007 9:08 pm
Location: USA, Michigan

Postby osborni » Thu Apr 03, 2014 12:43 am

Since you are welding on a target. Just double or triple it and see what happens
BMW 2000 M Coupe

Megablade
Posts: 6
Joined: Sat May 19, 2012 8:30 am
Location: Stuttgart/Germany

Postby Megablade » Thu Apr 03, 2014 4:49 am

Turby wrote:I use exactly the same sensor for my wheel speed BUT a) I use teh back of the wheel studs instead of a bit welded to the disc (stud is around 20mm diameter) and b) the sensor interfaces directly into a Motec M4 ecu. Works fine up to 210 kmh.

Do you have a pull up resistor between +5v and wheel speed output ?

According to http://www.race-technology.com/wiki/ind ... WheelSpeed 1ms is enough for pulse detection for rpm input or 0.5ms for frequency input.


Yes, I use the recommended pull up resistor. And unfortunately I cannot use the studs since the wheel bearing housing is too large. I will try it with 45mm irons and look what happens...

Megablade
Posts: 6
Joined: Sat May 19, 2012 8:30 am
Location: Stuttgart/Germany

Postby Megablade » Sun Apr 06, 2014 6:37 pm

IT WOOOOORKS!!!! :D

The irons have been enlarged and the engine speed is taken directly from the ground switched ignition coil. Thanks for the great support in the chat!

Here's a video of my first test drive today: https://www.youtube.com/watch?v=zbMJKOZ ... e=youtu.be


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