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Speed sensor erratic


Lotussuper7

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20210705_164321_copy_1079x720.thumb.jpg.f6803a072bd98d1c4521d32fa176bd22.jpgHi guys.

Trying to get my rear wheel speed sensor reading from my speedo output of the gear box. I have it hooked up and it's working (sort of). However the reading is erratic. It generally tracked the front wheel speed, however, looks like its had way to much coffee.

The orange trace is the front wheel speed measured of the front hub bolts using a gear tooth sensor, looks to give a nice stable speed trace?.

The white trace is from the gearbox speed sensor cable drive output, using a angle drive and a speed sensor from a Ford Ka (non oem ebay). Powered from battery voltage.

My question is, does the repetitive pattern look like a sensor fault, or could it come from either the gearbox speed output gears being damaged, or a binding in the angle drive(seems smooth to rotate by hand, and freshly lubricated)

Looking at how often the pattern repeats in such small time periods makes me believe it is the sensor, not a mechanical issue. But I would love others opinions before I go replacing things.

 

Any advice appreciated.

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It looks to me like it's could be the cable binding slightly, then jumping - there's a slowdown, then a sudden increase, then the next couple of signals are slightly faster and slightly slower than your smooth wheel speed.

Can you add a similar sensor on the rear wheels as you've got on the front? That looks to be giving you a very nice smooth speed signal.

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You could pull the sensor out and spin it with something constant speed such as a cordless drill to see if it is the drive side or the electronic side that is causing the "noise".

I believe the firmware engineers are working on some user configurable filtering on the DI's so you may be able to reduce this noise in software in a future update.  For now you could try using a math block as per Simons example here:

 

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The speed sensor I'm using passes the cable output through it, I wanted to get it going with this sensor so I can also keep my original Smiths speedo (has the cars odometer on it) it was the only sensor I could find with that option.

Using a sensor like the one I used on the front wheel on the gearbox output would be a real pain, as I would have to do some major engineering to make it work. If I were to go that way it would be easier to read the driveshaft yoke, this would also require a lot of work including removing the engine and gearbox as it is not accessible otherwise. Hence why I'm trying to use this sensor and the gearbox output.

The readings taken in the log are without the cable going to the speedo connected. So just the 90* drive and the sensor. The angle drive does use a flex shaft for its input, however, it is very short( within the drive casing ) so I'm unsure if that would cause it, but anything is possible. Do you think the short flex cable within the angle drive could cause this, looking at the frequency the pattern repeats. 

 

Should the di input Duty cycle oscillate that much on a vss (3 wire)

Thanks for your input. 

Thanks Adam for your reply. I did try it using the drill before I installed it, and it did seem to have a bit of noise, however, I put it down to the drill not keeping a constant speed when unloaded.  Wish I had an oscilloscope handy... The g4x can't look at the di inputs with the internal trigger scope can it?

 

Should the di Duty cycle be more consistent do you think? 

The sensor was brand new, but from ebay, and not a genuine Ford item.

Thanks for the tip on averaging the input value, I have previously set this up for the front wheel speed just to see it working (don't think the front needs averaging). Can you use a math block as the input for the driving  wheel speed?

 

Thanks for the input 

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I wasn't suggesting to change anything on the gearbox output - but picking up on propshaft, driveshaft or wheel studs etc.

I've added a sensor to my front wheel which picks up on bolts on the back of the front hub that hold the brake disk on - could you do something similar with the rear wheels?

VD3IRWEoHITSvRrRwLhOxFnSbHYXpot2cRNcbqcwnvv4lnJZenTtV9l_r1HN6eGkoN06W25w5qgWIe-GFcnXyfJhMb3_pigFJYKF0YiTjzveBBbxpPYPoiAPAfK4LPQl1sIj3QTfOwXm4NTWbgDI3LnHafCgF0ySYV-_ZRRmkFLTyW3WNHrOZ0IIZXxdIWFy2Nr_WH_G8EpEl-1nFyIEBqfkirf-EyXztPF3SMGwhR_mh976Sn6nhztzHbOT2wCF3fSk8mxzufKN2RM3NPT-UPGP4zY5lchh4jZtX-QL-2BCsLCBtNt8ObbtHE6R0gK_-f1lJA7YlzS__q752YkqVIS_hxwj2v9JWl-uBLOi5y0ck36Ey-WsTVVCbIZziX4hwS0d3uipmN8R7FktnE8QscltOoQeo05R9x0YECFMuuDDiBXuYIuJMrETFIxw529byhc0K0isd4_JF0QEualqKFLwmkJD30EhN5mJZKtpZV7UMjCqJEr2Gv0epEJrm2gqGfHu3VXX4tka6N1hy-oe4mGOh84bhAH1rU_Z1uPSVQs093-n3vyICPc_8nTpFaC27xNU_YWor9lQUw1CN80d2Ti_O5qjU4pg0hsazxdLdr0p33eBGrqUXT5PjD0XMwheqLfVOsRNivMxEmbJ2UbjpkUVL9BB0RGnIJqGfeHdKJKOdrkycVsVYI5feaKGUh7qBDTg95bSINZ2Ta1zSaj2FQA=w1190-h1586-no?authuser=0

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18 minutes ago, Tim Ward said:

The g4x can't look at the di inputs with the internal trigger scope can it?

DI1-4 are captured in the triggerscope.  Not the actual analog waveform that a real scope would give you, but the waveform that is sent to the processor after the initial hardware threshold etc is applied

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Its connected to di5, so that wouldn't have worked regardless. Thanks for the info.

Would your guess be a sensor fault, or a mechanical fault based on the frequency of the oscillation and the short time period the oscillation take place in?

10 minutes ago, Confused said:

I wasn't suggesting to change anything on the gearbox output - but picking up on propshaft, driveshaft or wheel studs etc.

I've added a sensor to my front wheel which picks up on bolts on the back of the front hub that hold the brake disk on - could you do something similar with the rear wheels?

VD3IRWEoHITSvRrRwLhOxFnSbHYXpot2cRNcbqcwnvv4lnJZenTtV9l_r1HN6eGkoN06W25w5qgWIe-GFcnXyfJhMb3_pigFJYKF0YiTjzveBBbxpPYPoiAPAfK4LPQl1sIj3QTfOwXm4NTWbgDI3LnHafCgF0ySYV-_ZRRmkFLTyW3WNHrOZ0IIZXxdIWFy2Nr_WH_G8EpEl-1nFyIEBqfkirf-EyXztPF3SMGwhR_mh976Sn6nhztzHbOT2wCF3fSk8mxzufKN2RM3NPT-UPGP4zY5lchh4jZtX-QL-2BCsLCBtNt8ObbtHE6R0gK_-f1lJA7YlzS__q752YkqVIS_hxwj2v9JWl-uBLOi5y0ck36Ey-WsTVVCbIZziX4hwS0d3uipmN8R7FktnE8QscltOoQeo05R9x0YECFMuuDDiBXuYIuJMrETFIxw529byhc0K0isd4_JF0QEualqKFLwmkJD30EhN5mJZKtpZV7UMjCqJEr2Gv0epEJrm2gqGfHu3VXX4tka6N1hy-oe4mGOh84bhAH1rU_Z1uPSVQs093-n3vyICPc_8nTpFaC27xNU_YWor9lQUw1CN80d2Ti_O5qjU4pg0hsazxdLdr0p33eBGrqUXT5PjD0XMwheqLfVOsRNivMxEmbJ2UbjpkUVL9BB0RGnIJqGfeHdKJKOdrkycVsVYI5feaKGUh7qBDTg95bSINZ2Ta1zSaj2FQA=w1190-h1586-no?authuser=0

Thanks for the suggestion, This is similar to the setup I have on the front wheel, However I am hesitant to do this because there is no wiring for rear wheel speed, and it would be a real pita to add it. So was hoping to get this gearbox setup working as it is accessible without removing the engine and gearbox (just), the car is very compact and hard to work on in many respects. Especially routing things to the back of the car (it has a completely sealed bottom, tunnel included.) Reading rear wheel speed of a single wheel can be problematic if you lift a wheel too, so I would then need two sensors and average the results.

Appreciate everyone's input.

 

Thanks 

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Another thing I noticed is the sensor seems to work no matter what di settings I have...

 

ie: Pull up on or off

     Leading or trailing edge (I know this wont make any real difference due to it being frequency based)

     and any combination or those settings all work, not well obviously, but it does work....

     Pretty sure its just a hall sensor, as I have taken it apart and it just seems like a spinning disk with magnets imbedded.(and a encased sensor)

    Wouldn't turning on or of the internal pullup stop the sensor working in one of those states? Just curious.

 

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Would a reed type be 3 wires? I would have had a look at the sensor, but I think you would need to break into the housing to see it, looks glued to me.

 

This is the one I used

 

From Various ford models, fiesta Ka and a few others I think.

 

download.jpgsensor.jpg

9 minutes ago, Adamw said:

Many digital type sensors have a pull-up built in.  It could be a reed switch type or hall effect.  

That makes sense about the pull up then. Didn't think of that. 

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Update to this topic:

I remembered that I had another miniature hall sensor, so i taped it to the side of the vss sensor housing, wired it up and managed to get a reading. The erratic behavior continued. So I have come to the conclusion that it is most likely the angle drive or the internal gear output etc

I have now set up a math block that has smoothed the output for the sensor. Hopefully it is stable enough. The averaging works well.

 

For anyone else wanting to smooth their wheel speeds, this is how I did it:

 

1. Set up a di for all your different speed sources.

 

2. Set up a math channel for the wheel you want to average, with the di you selected for that wheel as the first parameter (a). Equation = av(a,0.1)

3. Set up a gp speed input(s) for the front or rear wheels (or both), with the math channel you created above as the input. (two inputs needed if smoothing both driven and driving wheel speeds.)

 

4. Select the gp speed source you created above as your driven or driving wheel speed source.

 

You can get more of less averaging by increasing the value in the math equation. Just remember averaging causes a delay in value creation, so use the smallest value that gives adequate results.

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  • 2 weeks later...

Further update to this topic. After a few very frustrating days trying to figure out what was going on I think I finally have this sorted. 

I have found out that the cheap sensor I purchased was rubbish, the armature that spins inside was not captured in the housing properly and was allowed to move in and out, this made the readings from the sensor  very erratic. The magnets were also very weak, so I think that was why I got more erratic readings when using another hall sensor temporarily taped to the side.

I have done some ' modifications' to the sensor, including drilling holes in the armature and fitting some new magnets, replacing the bushings with bearings, including thrust bearings and gutting the electronics and replacing them with a new barrel type hall sensor. Now the Vss sensor works fine, although there isnt much of the original sensor left. 

What I have learned from this is the sensor has to be exactly in the right place relative to the armature, or the speed reading gets very erratic. Literally a fraction of a mm can be the difference between success or failure. I used epoxy to lock the sensor in place when I managed to get a good reading. 

Hopefully road testing shows good results, however, rain and no roof is stopping that happening. 

Maybe this will be helpful for someone else.

 

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